Chapter 17: Minerals

Similar to vitamins, minerals are essential to human health and can be obtained in our diet from different types of food. Minerals are abundant in our everyday lives. From the soil in your front yard to the jewelry you wear on your body, we interact with minerals constantly. There are 20 essential minerals that must be consumed in our diets to remain healthy.  The amount of each mineral found in our bodies vary greatly and therefore, so does consumption of those minerals. When there is a deficiency in an essential mineral, health problems may arise.

Major minerals are classified as minerals that are required in the diet each day in amounts larger than 100 milligrams. These include sodium, potassium, chloride, calcium, phosphorus, magnesium, and sulfur. These major minerals can be found in various foods. For example, in Guam, the major mineral, calcium, is consumed in the diet not only through dairy, a common source of calcium, but also through through the mixed dishes, desserts and vegetables that they consume. Consuming a varied diet significantly improves an individual’s ability to meet their nutrient needs.^[1]

 

Bioavailability

Minerals are not as efficiently absorbed as most vitamins and so the bioavailability of minerals can be very low. Plant-based foods often contain factors, such as oxalate and phytate, that bind to minerals and inhibit their absorption. In general, minerals are better absorbed from animal-based foods. In most cases, if dietary intake of a particular mineral is increased, absorption will decrease. Some minerals influence the absorption of others. For instance, excess zinc in the diet can impair iron and copper absorption. Conversely, certain vitamins enhance mineral absorption. For example, vitamin C boosts iron absorption, and vitamin D boosts calcium and magnesium absorption. As is the case with vitamins, certain gastrointestinal disorders and diseases, such as Crohn’s disease and kidney disease, as well as the aging process, impair mineral absorption, putting people with malabsorption conditions and the elderly at higher risk for mineral deficiencies.

References

1. Pobocik RS, Trager A, Monson LM. Dietary Patterns and Food Choices of a Population Sample of Adults on Guam. Asia Pacific Journal of Clinical Nutrition. 2008; 17(1), 94-100. http://apjcn.nhri.org.tw/server/APJCN/17/1/94.pdf.

Minerals and Bone Health

Bone is comprised of cells embedded in a collagen framework surrounded by mineral deposits of calcium phosphate in a form known as hydroxylapatite [Ca₅(PO₄)₃(OH)]. Sufficient levels of both calcium and phosphate are necessary for bone health. Magnesium, although not a major component of bones, is critical to proper calcium homeostasis and plays an important role in bone health.

Calcium’s Functional Roles

Calcium is the most abundant mineral in the body and greater than 99 percent of it is stored in bone tissue. Although only 1 percent of the calcium in the human body is found in the blood and soft tissues, it is here that it performs the most critical functions. Blood calcium levels are rigorously controlled so that if blood levels drop the body will rapidly respond by stimulating bone resorption, thereby releasing stored calcium into the blood.  Thus, bone tissue sacrifices its stored calcium to maintain blood calcium levels. This is why bone health is dependent on the intake of dietary calcium and also why blood levels of calcium do not always correspond to dietary intake.

Calcium plays a role in a number of different functions in the body like bone and tooth formation. The most well-known calcium function is to build and strengthen bones and teeth. Recall that when bone tissue first forms during the modeling or remodeling process, it is unhardened, protein-rich osteoid tissue. In the osteoblast-directed process of bone mineralization, calcium phosphates (salts) are deposited on the protein matrix. The calcium salts typically make up about 65 percent of bone tissue. When your diet is calcium deficient, the mineral content of bone decreases causing it to become brittle and weak. Thus, increased calcium intake helps to increase the mineralized content of bone tissue. Greater mineralized bone tissue corresponds to a greater bone density and greater bone strength.

Importantly, calcium plays a role in nerve impulse transmission by facilitating electrical impulse transmission from one nerve cell to another. Calcium in muscle cells is essential for muscle contraction because the flow of calcium ions is needed for the muscle proteins (actin and myosin) to interact. Calcium is also essential in blood clotting by activating clotting factors to fix damaged tissue.

In addition, calcium is an important signaling molecule within cells and is critical to exocytosis of a number of hormones. For example, without calcium, the hormone insulin could not be released from cells in the pancreas and glycogen could not be broken down in muscle cells and used to provide energy for muscle contraction.

Maintaining Calcium Levels

Because calcium performs such vital functions in the body, blood calcium level is closely regulated by the hormones parathyroid hormone (PTH), calcitriol, and calcitonin. When blood calcium levels are low, PTH is secreted to increase blood calcium levels via three different mechanisms. First, PTH stimulates the release of calcium stored in the bone. Second, PTH acts on kidney cells to increase calcium reabsorption and decrease its excretion in the urine. Third, PTH stimulates enzymes in the kidney that activate vitamin D to calcitriol.  Calcitriol is the active hormone that acts on the intestinal cells and increases dietary calcium absorption. When blood calcium levels become too high, the hormone calcitonin is secreted by certain cells in the thyroid gland and PTH secretion stops.  At higher non-physiological concentrations, calcitonin lowers blood calcium levels by increasing calcium excretion in the urine, preventing further absorption of calcium in the gut and by directly inhibiting bone resorption.

Other Health Benefits of Calcium in the Body

Besides forming and maintaining strong bones and teeth, calcium has been shown to have other health benefits for the body, including:

• Cancer. Higher intakes of calcium decrease colon cancer risk and may suppress the growth of polyps that often precipitate cancer. Although higher calcium consumption protects against colon cancer, some studies have looked at the relationship between calcium and prostate cancer and found higher intakes may increase the risk for prostate cancer; however, the data is inconsistent and more studies are needed to confirm any negative association.
• Blood pressure. Multiple studies provide clear evidence that higher calcium consumption reduces blood pressure. A review of twenty-three observational studies concluded that for every 100 milligrams of calcium consumed daily, systolic blood pressure is reduced 0.34 millimeters of mercury (mmHg) and diastolic blood pressure is decreased by 0.15 mmHg.^[1]
• Cardiovascular health. There is emerging evidence that higher calcium intakes prevent against other risk factors for cardiovascular disease, such as high cholesterol and obesity, but the scientific evidence is weak or inconclusive.
• Kidney stones. Another health benefit of a high-calcium diet is that it blocks kidney stone formation. Calcium inhibits the absorption of oxalate, a chemical in plants such as parsley and spinach, which is associated with an increased risk for developing kidney stones. Calcium’s protective effects on kidney stone formation occur only when you obtain calcium from dietary sources. Calcium supplements may actually increase the risk for kidney stones in susceptible people.

Calcium inadequacy is most prevalent in adolescent girls and the elderly. Proper dietary intake of calcium is critical for proper bone health.

Despite the wealth of evidence supporting the many health benefits of calcium (particularly bone health), the average American diet falls short of achieving the recommended dietary intakes of calcium. Here we will take a closer look at particular groups of people who may require extra calcium intake.

• Adolescent teens. A calcium-deficient diet is common in teenage girls as their dairy consumption often considerably drops during adolescence.
• Amenorrheic women and the “female athlete triad”. Amenorrhea refers to the absence of a menstrual cycle. Women who fail to menstruate suffer from reduced estrogen levels, which can disrupt and have a negative impact on the calcium balance in their bodies. The “female athlete triad” is a combination of three conditions characterized by amenorrhea, disrupted eating patterns, and osteoporosis. Exercise-induced amenorrhea and anorexia nervosa-related amenorrhea can decrease bone mass.^{[2, 3]} In female athletes, as well as active women in the military, low BMD, menstrual irregularities, and individual dietary habits together with a history of previous stress issues are related to an increased susceptibility to future stress fractures.^{[4, 5]}
• The elderly. As people age, calcium bioavailability is reduced, the kidneys lose their capacity to convert vitamin D to its most active form, the kidneys are no longer efficient in retaining calcium, the skin is less effective at synthesizing vitamin D, there are changes in overall dietary patterns, and older people tend to get less exposure to sunlight. Thus the risk for calcium inadequacy is great.^[6]
• Postmenopausal women. Estrogen enhances calcium absorption. The decline in this hormone during and after menopause puts postmenopausal women especially at risk for calcium deficiency. Decreases in estrogen production are responsible for an increase in bone resorption and a decrease in calcium absorption. During the first years of menopause, annual decreases in bone mass range from 3–5 percent. After age sixty-five, decreases are typically less than 1 percent.^[7]
• Lactose-intolerant people. Groups of people, such as those who are lactose intolerant, or who adhere to diets that avoid dairy products, may not have an adequate calcium intake.
• Vegans. Vegans may absorb reduced amounts of calcium because their diets favor plant-based foods that contain oxalates and phytates, which decrease calcium absorption.^[8]

In addition, because vegans avoid dairy products, their overall consumption of calcium-rich foods may be less.

If you are lactose intolerant, have a milk allergy, are a vegan, or you simply do not like dairy products, remember that there are many plant-based foods that have a good amount of calcium and there are also some low-lactose and lactose-free dairy products on the market.

Calcium Supplements: Which One to Buy?

Many people choose to fulfill their daily calcium requirements by taking calcium supplements. Calcium supplements are sold primarily as calcium carbonate, calcium citrate, calcium lactate, and calcium phosphate, with elemental calcium contents of about 200 milligrams per pill. It is important to note that calcium carbonate requires an acidic environment in the stomach to be used effectively. Although this is not a problem for most people, it may be for those on medication to reduce stomach-acid production or for the elderly who may have a reduced ability to secrete acid in the stomach. For these people, calcium citrate may be a better choice. Otherwise, calcium carbonate is the cheapest. The body is capable of absorbing approximately 30 percent of the calcium from these forms.

Beware of Lead

Calcium supplements derived from natural sources such as oyster shell, bone meal, and dolomite (a type of rock containing calcium magnesium carbonate) are known to contain high amounts of lead. In one study conducted on twenty-two brands of calcium supplements, eight of the brands exceeded the acceptable limit for lead content. This was found to be the case in supplements derived from oyster shell and refined calcium carbonate. The same study also found that brands claiming to be lead-free did, in fact, show very low lead levels. Because lead levels in supplements are not disclosed on labels, it is important to know that products not derived from oyster shell or other natural substances are generally low in lead content. In addition, it was also found that one brand did not disintegrate as is necessary for absorption, and one brand contained only 77 percent of the stated calcium content.^[9]

Diet, Supplements, and Chelated Supplements

In general, calcium supplements perform to a lesser degree than dietary sources of calcium in providing many of the health benefits linked to higher calcium intake. This is partly attributed to the fact that dietary sources of calcium supply additional nutrients with health-promoting activities. It is reported that chelated forms of calcium supplements are easier to absorb as the chelation process protects the calcium from oxalates and phytates that may bind with the calcium in the intestines. However, these are more expensive supplements and only increase calcium absorption up to 10 percent. In people with low dietary intakes of calcium, calcium supplements have a negligible benefit on bone health in the absence of a vitamin D supplement. However, when calcium supplements are taken along with vitamin D, there are many benefits to bone health: peak bone mass is increased in early adulthood, bone density is maintained throughout adulthood, the risk of developing osteoporosis is reduced, and the incidence of fractures is decreased in those who already had osteoporosis. Calcium and vitamin D pills do not have to be taken at the same time for effectiveness. But remember that vitamin D has to be activated and in the bloodstream to promote calcium absorption. Thus, it is important to maintain an adequate intake of vitamin D.

Dietary Reference Intake for Calcium

The recommended dietary allowances (RDA) for calcium is elevated to 1,300 milligrams per day during adolescence because this is the life stage with accelerated bone growth. Studies have shown that a higher intake of calcium during puberty increases the total amount of bone tissue that accumulates in a person. For women above age fifty and men older than seventy-one, the RDAs are also a bit higher for several reasons including that as we age, calcium absorption in the gut decreases, vitamin D3 activation is reduced, and maintaining adequate blood levels of calcium is important to prevent an acceleration of bone tissue loss (especially during menopause). Currently, the dietary intake of calcium for females above age nine is, on average, below the RDA for calcium. The Institute of Medicine (IOM) recommends that people do not consume over 2,500 milligrams per day of calcium as it may cause adverse effects in some people.

Table 17.1 Dietary Reference Intakes for Calcium. Source: Calcium – Health Professional Fact Sheet. National Institutes of Health, Office of Dietary Supplements. Updated July 11, 2025. Accessed August 25, 2025. Public domain.

Age Group	RDA (or AI*) (mg/day)	UL (mg/day)
Infants (0–6 months)	200*	1,000
Infants (6–12 months)	260*	1,500
Children (1–3 years)	700	2,500
Children (4–8 years)	1,000	2,500
Children (9–13 years)	1,300	3,000
Adolescents (14–18 years)	1,300	3,000
Adults (19–50 years)	1,000	2,500
Adults (50–71 years)	1,000 (males), 1,200 (females)	2,000
Adults (> 71 years)	1,200	2,000

Dietary Sources of Calcium

In the typical American diet, calcium is obtained mostly from dairy products, primarily cheese. A slice of cheddar or Swiss contains just over 200 milligrams of calcium. One cup of nonfat milk contains approximately 300 milligrams of calcium, about a third of the RDA for calcium for most adults. Foods fortified with calcium such as cereals, soy milk, and orange juice also provide one third or greater of the calcium RDA. Although the typical American diet relies mostly on dairy products for obtaining calcium, there are other good non-dairy sources of calcium.

Adequate calcium can also be obtained through non-dairy sources. Tofu (made with calcium sulfate), turnip greens, mustard greens, and chinese cabbage are good sources. For a list of non-dairy sources, you can find the calcium content for thousands of foods by visiting the USDA FoodData Central (https://fdc.nal.usda.gov/). When obtaining your calcium from a vegan diet, it is important to know that some plant-based foods significantly impair the absorption of calcium. These include spinach, Swiss chard, rhubarb, beets, cashews, and peanuts. With careful planning and good selections, you can ensure that you are getting enough calcium in your diet even if you do not drink milk or consume other dairy products.

Table 17.2 Calcium Content of Various Foods. Source: Calcium – Health Professional Fact Sheet. National Institutes of Health, Office of Dietary Supplements. Updated July 11, 2025. Accessed March 3, 2026. Public domain.

Food	Serving	Calcium (mg)	Percent Daily Value
Yogurt, low fat	8 oz.	415	32
Mozzarella cheese, part skim	1.5 oz.	333	26
Sardines, canned with bones	3 oz.	325	25
Milk, nonfat	8 oz.	299	23
Soymilk, calcium fortified	8 oz.	299	23
Tofu, firm, made with calcium sulfate	½ c.	253	19
Salmon, canned with bones	3 oz.	181	14
Turnip greens, boiled	½ c.	99	8
Whole wheat bread	1 slice	30	2
Kale, raw	1 c.	24	2
Broccoli, raw	½ c.	21	2

Calcium Bioavailability

In the small intestine, calcium absorption primarily takes place in the duodenum (first section of the small intestine) when intakes are low, but calcium is also absorbed passively in the jejunum and ileum (second and third sections of the small intestine), especially when intakes are higher. The body doesn’t completely absorb all the calcium in food. Interestingly, the calcium in some vegetables such as kale, Brussels sprouts, and bok choy is better absorbed by the body than are dairy products. About 30 percent of calcium is absorbed from milk and other dairy products.

The greatest positive influence on calcium absorption comes from having an adequate intake of vitamin D. People deficient in vitamin D absorb less than 15 percent of calcium from the foods they eat. The hormone estrogen is another factor that enhances calcium bioavailability. Thus, as menopause, when estrogen levels fall, decreases the amount of calcium absorbed and increases the risk for bone disease. Some fibers, such as inulin, found in jicama, onions, and garlic, also promote calcium intestinal uptake.

Chemicals that bind to calcium decrease its bioavailability. These negative effectors of calcium absorption include the oxalates in certain plants, the tannins in tea, phytates in nuts, seeds, and grains, and some fibers. Oxalates are found in high concentrations in spinach, parsley, cocoa, and beets. In general, the calcium bioavailability is inversely correlated to the oxalate content in foods. High-fiber, low-fat diets also decrease the amount of calcium absorbed, an effect likely related to how fiber and fat influence the amount of time food stays in the gut. Anything that causes diarrhea, including sickness, medications, and certain symptoms related to old age, decreases the transit time of calcium in the gut and therefore decreases calcium absorption. As we get older, stomach acidity sometimes decreases, diarrhea occurs more often, kidney function is impaired, and vitamin D absorption and activation is compromised, all of which contribute to a decrease in calcium bioavailability.

References

1. Birkett NJ. Comments on a Meta-Analysis of the Relation between Dietary Calcium Intake and Blood Pressure. Am J Epidemiol. 1998;148(3), 223–28.https://doi.org/10.1093/oxfordjournals.aje.a009627.  
2. Drinkwater B, Bruemner B, Chesnut C. Menstrual History As a Determinant of Current Bone Density in Young Athletes. JAMA. 1990; 263(4), 545–8. https://jamanetwork.com/journals/jama/fullarticle/vol/263/pg/545. 
3. Marcus R. et al. Menstrual Function and Bone Mass in Elite Women Distance Runners: Endocrine and Metabolic Features. Ann Intern Med. 1985; 102(2), 58–63. https://www.acpjournals.org/doi/10.7326/0003-4819-102-2-158.
4. Nattiv A. Stress Fractures and Bone Health in Track and Field Athletes. J Sci Med Sport. 2000;  3(3), 268–79. https://doi.org/10.1016/S1440-2440(00)80036-5.
5. Johnson AO, et al. Correlation of Lactose Maldigestion, Lactose Intolerance, and Milk Intolerance. Am J Clin Nutr. 1993; 57(3), 399–401. https://doi.org/10.1093/ajcn/57.3.399.
6. Nutrition. International Osteoporosis Foundation. https://www.osteoporosis.foundation/health-professionals/prevention/nutrition. Accessed August 25, 2025.
7. Daniels CE. Estrogen Therapy for Osteoporosis Prevention in Postmenopausal Women. National Institute of Health: Pharmacy Update, March/April 2001. https://webharvest.gov/peth04/20041101222419/http://www.cc.nih.gov/phar/updates/Aprupdate01.pdf. Accessed August 25, 2025.
8. Calcium – Health Professional Fact Sheet. National Institutes of Health, Office of Dietary Supplements. https://ods.od.nih.gov/factsheets/Calcium-HealthProfessional/. Updated July 11, 2025. Accessed March 3, 2026.
9. Ross EA, Szabo NJ, Tebbett IR. Lead Content of Calcium Supplements. JAMA. 2000; 284, 1425–33. https://doi.org/10.1001/jama.284.11.1425.
10. Bolland MJ. et al. Effect of Calcium Supplements on Risk of Myocardial Infarction and Cardiovascular Events: Meta-Analysis. Br Med J. 2010;  341(c3691). https://doi.org/10.1136/bmj.c3691.

Phosphorus’s Functional Role

Phosphorus is present in our bodies as part of a chemical group called a phosphate group. These phosphate groups are essential as a structural component of cell membranes (as phospholipids), a core feature of nucleotides including ATP used as cellular energy, and the nucleic acids made from nucleotides, our DNA and RNA. Phosphorous salts with calcium form the mineral deposits in our bones. Phospate groups also are used to modify proteins as a form of signaling inside of cells, and phosphate groups in the blood and interstitial fluids can help regulate pH.

Blood phosphorus levels are not controlled as strictly as calcium so the PTH stimulates renal excretion of phosphate so that it does not accumulate to toxic levels.

Dietary Reference Intakes for Phosphorus

In comparison to calcium, most Americans are not at risk for having a phosphate deficiency. Phosphate is present in many foods popular in the American diet including meat, fish, dairy products, processed foods, and beverages. Phosphate is added to many foods because it acts as an emulsifying agent, prevents clumping, improves texture and taste, and extends shelf-life. The average intake of phosphorus in US adults ranges between 1,000 and 1,500 milligrams per day, well above the RDA of 700 milligrams per day. The UL set for phosphorous is 4,000 milligrams per day for adults and 3,000 milligrams per day for people over age seventy.

Table 17.3 Dietary Reference Intakes for Phosphorus.  Source: Phosphorus – Health Professional Fact Sheet. National Institutes of Health, Office of Dietary Supplements. Updated May 4, 2023. Accessed August 25, 2025. Public domain.

Age Group	RDA (or AI*) (mg/day)	UL (mg/day)
Infants (0–6 months)	100*	–
Infants (7–12 months)	275*	–
Children (1–3 years)	460	3,000
Children (4–8 years)	500	3,000
Children (9–13 years)	1,250	4,000
Adolescents (14–18 years)	1,250	4,000
Adults (19–70 years)	700	4,000
Adults (> 70 years)	700	3,000

Dietary Sources of Phosphorus

Table 17.4 Phosphorus Content of Various Foods. Source: Phosphorus – Health Professional Fact Sheet. National Institutes of Health, Office of Dietary Supplements. Updated May 4, 2023.Accessed March 3, 2026. Public domain.

Foods	Serving	Phosphorus (mg)	Percent Daily Value
Yogurt, low fat	6 oz.	245	20
Salmon	3 oz.	214	17
Chicken breast	3 oz.	182	15
Ground beef, 90% lean	3 oz.	172	14
Potato, russet, baked	1 medium	123	10
Brown rice	½ c.	102	8
Egg, hard boiled	1 large	86	7
Apple	1 medium	20	2

Phosphorus and the Environment

All animals, plants, and even bacteria require phosphorous. Historically, food production was localized and phosphate consumed by humans and animals returned to the soil, either as human manure, compost, or other waste. In our current global network of food production, much food and the phosphorous therein, are consumed far from where the food way grown. In this model, the phosphorus is not returned to the soil for the next round of plants. Indeed, modern farming methods rely heavily on fertilizers that have phosphorous, as well as nitrogen and potassium, as a major constituent. Much of this phosphorous comes from phosphate rock. Because of the abundance of phosphate rock and the ease of mining it, this has been an economical solution, but run-off from the phosphorus-heavy fertilizer leads to eutrophication, a severe form on an algae bloom where the algae bloom then die. This can change the area into an oxygen-poor dead zone.

Magnesium’s Functional Role

Approximately 60 percent of magnesium in the human body is stored in the skeleton, making up about 1 percent of mineralized bone tissue. Magnesium is not an integral part of the hard mineral crystals, but it does reside on the surface of the crystal and helps maximize bone structure. Observational studies link magnesium deficiency with an increased risk for osteoporosis. A magnesium-deficient diet is associated with decreased levels of parathyroid hormone and the activation of vitamin D, which may lead to an impairment of bone remodeling. A study in nine hundred elderly women and men did show that higher dietary intakes of magnesium correlated to an increased BMD in the hip.^[1] Only a few clinical trials have evaluated the effects of magnesium supplements on bone health and their results suggest some modest benefits on bone density.

In addition to participating in bone maintenance, magnesium has several other functions in the body. In every reaction involving the cellular energy molecule, ATP, magnesium is required. More than three hundred enzymatic reactions require magnesium. Magnesium plays a role in the synthesis of DNA and RNA, carbohydrates, and lipids, and is essential for nerve conduction and muscle contraction. Another health benefit of magnesium is that it may decrease blood pressure.

Many Americans do not get the recommended intake of magnesium from their diets. Some observational studies suggest mild magnesium deficiency is linked to increased risk for cardiovascular disease. Signs and symptoms of severe magnesium deficiency may include tremor, muscle spasms, loss of appetite, and nausea.

Dietary Reference Intake and Food Sources for Magnesium

The RDAs for magnesium for adults between ages nineteen and thirty are 400 milligrams per day for males and 310 milligrams per day for females. For adults above age thirty, the RDA increases slightly to 420 milligrams per day for males and 320 milligrams for females. Excessive magnesium intake is usually the result to supplementation; the ULs in Table 17.5 are only for magnesium taken via supplements, not that ingested as part of food.

Table 17.5 Dietary Reference Intakes for Magnesium. Source:  Magnesium – Health Professional Fact Sheet. National Institutes of Health, Office of Dietary Supplements. Updated June 2, 2022. Accessed August 25, 2025. Public domain.

Age Group	RDA (or AI*) (mg/day)	UL from non-food sources (mg/day)
Infants (0–6 months)	30*	–
Infants (6–12 months)	75*	–
Children (1–3 years)	80	65
Children (4–8 years)	130	110
Children (9–13 years)	240	350
Adolescents (14–18 years)	410 (males), 360 (females)	350
Adults (19–30 years)	400 (males), 310 (females)	350
Adults (> 30 years)	420 (males), 320 (females)	350

Dietary Sources of Magnesium

Magnesium is part of the green pigment, chlorophyll, which is vital for photosynthesis in plants; therefore, green leafy vegetables are a good dietary source for magnesium. Magnesium is also found in high concentrations in fish, dairy products, meats, whole grains, and nuts. Additionally, chocolate, coffee, and hard water contain a good amount of magnesium. Most people in America do not fulfill the RDA for magnesium in their diets. Typically, Western diets lean toward a low fish intake and the unbalanced consumption of refined grains versus whole grains.

Table 17.6 Magnesium Content of Various Foods. Source:  Magnesium – Health Professional Fact Sheet. National Institutes of Health, Office of Dietary Supplements. Updated June 2, 2022. Accessed March 3, 2026. Public domain.

Food	Serving	Magnesium (mg)	Percent Daily Value
Almonds, dry roasted	1 oz.	80	19
Cashews, dry roasted	1 oz.	74	18
Soymilk	1 c.	61	15
Black beans, cooked	½ c.	60	14
Edamame, shelled, cooked	½ c.	50	12
Peanut butter, smooth	2 tbsp.	49	12
Kidney beans, canned	½ c.	35	8
Salmon	3 oz.	26	6
Chicken breasts	3 oz.	22	6
Apple	1 medium	9	2

References

1. Tucker KL, Hannan MT, et al. Potassium, Magnesium, and Fruit and Vegetable Intakes Are Associated with Greater Bone Mineral Density in Elderly Men and Women. Am J Clin Nutr. 1999; 69(4), 727–36. https://doi.org/10.1093/ajcn/69.4.727. 

Fluoride and Tooth Health

Fluoride is known mostly as the mineral that combats tooth decay. It assists in tooth and bone development and maintenance. Fluoride combats tooth decay via three mechanisms:

• Blocking acid formation by bacteria
• Preventing demineralization of teeth
• Enhancing remineralization of destroyed enamel

Fluoride was first added to drinking water in 1945 in Grand Rapids, Michigan; now over 60 percent of the US population consumes fluoridated drinking water. The Centers for Disease Control and Prevention (CDC) has reported that fluoridation of water prevents, on average, 27 percent of cavities in children and between 20 and 40 percent of cavities in adults. The CDC considers water fluoridation one of the ten great public health achievements in the twentieth century.^[1]

The optimal fluoride concentration in water to prevent tooth decay ranges between 0.7–1.2 milligrams per liter. Exposure to fluoride at three to five times this concentration before the growth of permanent teeth can cause fluorosis, which is the mottling and discoloring of the teeth.

 

Fluoride’s benefits to mineralized tissues of the teeth are well substantiated, but the effects of fluoride on bone are not as well known. Fluoride is currently being researched as a potential treatment for osteoporosis. The data are inconsistent on whether consuming fluoridated water reduces the incidence of osteoporosis and fracture risk. Fluoride does stimulate osteoblast bone building activity, and fluoride therapy in patients with osteoporosis has been shown to increase BMD. In general, it appears that at low doses, fluoride treatment increases BMD in people with osteoporosis and is more effective in increasing bone quality when the intakes of calcium and vitamin D are adequate. The Food and Drug Administration has not approved fluoride for the treatment of osteoporosis mainly because its benefits are not sufficiently known and it has several side effects including frequent stomach upset and joint pain. The doses of fluoride used to treat osteoporosis are much greater than that in fluoridated water.

References

1. Ten Great Public Health Achievements – United States, 1900-1999. Centers for Disease Control. Morbidity and Mortality Weekly Report. 1999; 48(12), 241–43. https://www.cdc.gov/mmwr/preview/mmwrhtml/00056796.htm. Accessed August 25, 2025.

Minerals and Fluid Balance

The human body is made up of mostly water, 50 to 75% of our weight, depending on age and sex. Although water makes up the largest percentage of body volume, it is not actually pure water but rather a mixture of cells, proteins, glucose, lipoproteins, electrolytes, and other substances. Electrolytes are substances that, when dissolved in water, dissociate into charged ions. Positively charged electrolytes are called cations and negatively charged electrolytes are called anions. For example, in water sodium chloride (the chemical name for table salt) dissociates into sodium cations (Na⁺) and chloride anions (Cl⁻). Solutes refers to all dissolved substances in a fluid, which may be charged, such as sodium (Na⁺), or uncharged, such as glucose. In the human body, water and solutes are distributed into two compartments: inside cells, called intracellular (~66% of total water), and outside cells, called extracellular (~33% of total water). The extracellular water compartment is subdivided into the blood plasma (~8% of total) and the remainder (25% of total), which includes the fluid found in interstitial spaces (between cells), cerebrospinal fluid which surrounds and protects the brain and spinal cord, lymph, fluid in synovial joints, etc. (Figure 17.4). The composition of solutes differs between the fluid compartments. For example, more protein is inside cells than outside and more chloride anions exist outside of cells than inside.

Fluid Balance and Osmoregulation

One of the essential homeostatic functions of the body is to maintain fluid balance and the differences in solute composition between cells and their surrounding environment. Osmoregulation is the control of fluid balance and composition in the body. The processes involved keep fluids from becoming too dilute or too concentrated. Fluid compartments are separated by selectively permeable membranes, which allow some things, such as water, to move through while other substances require special transport proteins, channels, and often energy. The movement of water between fluid compartments happens by osmosis, which is simply the movement of water through a selectively permeable membrane from an area where it is highly concentrated to an area where it is not so concentrated. Water is never transported actively; that is, it never takes energy for water to move between compartments. Although cells do not directly control water movement, they do control movement of electrolytes and other solutes and thus indirectly regulate water movement by controlling where there will be regions of high and low concentrations.

Cells maintain their water volume at a constant level, but the composition of solutes in a cell is in a continuous state of flux. This is because cells are bringing nutrients in, metabolizing them, and disposing of waste products. To maintain water balance, a cell controls the movement of electrolytes to keep the total concentration of dissolved particles, called osmolarity, the same inside and outside (Figure 17.5) The total number of dissolved substances is the same inside and outside a cell, but the composition of the fluids differs between compartments. For example, sodium exists in extracellular fluid at fourteen times the concentration as compared to that inside a cell.

Cells maintain water volume by actively controlling electrolyte concentrations. Human erythrocytes (red blood cells) are shown here. Three conditions are shown: hypertonic conditions (where the erythrocytes contract and appear “spiky”), isotonic conditions (where the erythrocytes appear normal) and hypotonic conditions (where the erythrocytes expand and become rounder).

If a cell is placed in a solution that contains fewer dissolved particles (hypotonic solution) than the cell itself, water moves into the more concentrated cell, causing it to swell. Alternatively, if a cell is placed in a solution that is more concentrated (known as a hypertonic solution) water moves from inside the cell to the outside, causing it to shrink. Cells keep their water volume constant by pumping electrolytes in and out in an effort to balance the concentrations of dissolved particles on either side of their membranes. When a solution contains an equal concentration of dissolved particles on either side of the membrane, it is known as an isotonic solution.

In the process of osmoregulation and overall regulation of water balance, we regulate water we consume by thirst, excreted water, and the balance between water and salts excreted. To maintain fluid balance, fluid intake must match fluid output (Figure 17.6). The Food and Nutrition Board of the Institute of Medicine (IOM) has set the Adequate Intake (AI) for total water for adult males at 3.7 liters (15.6 cups) and at 2.7 liters (11 cups) for adult females.^[1] These intakes are higher than the average intake of 2.2 liters. It is important to note that the AI for water includes water from all dietary sources—that is, water coming from food as well as beverages. People are not expected to consume 15.6 or 11 cups of pure water per day. In America, approximately 20 percent of dietary water comes from solid foods. A small amount of water is generated each day by the chemical reactions of metabolism, such as cellular respiration. Water loss routes include the skin, lungs, urine, and feces.

There is some debate over the amount of water required to maintain health because there is no consistent scientific evidence proving that drinking a particular amount of water improves health or reduces the risk of disease. In fact, kidney-stone prevention seems to be the only premise for water-consumption recommendations. You may be surprised to find out that the commonly held belief that people need to drink eight 8-ounce glasses of water per day isn’t an official recommendation and isn’t based on any scientific evidence! The amount of water/fluids a person should consume every day is actually variable and should be based on the climate a person lives in, as well as their age, physical activity level, and kidney function. No maximum for water intake has been set.

As stated, daily water output averages 2.5 liters. There are two types of outputs. The first type is insensible water loss, meaning we are unaware of it. The body loses about 400 milliliters of its daily water output through exhalation. Another 500 milliliters is lost through our skin. The second type of output is sensible water loss, meaning we are aware of it. Urine accounts for about 1,500 milliliters of water output, and feces account for roughly 100 milliliters of water output. Regulating urine output is a primary function of the kidneys, and involves communication with the brain and endocrine system.

Do you need 8 glasses of water a day?

The advice to drink at least eight 8oz glasses of water a day is a pervasive health care myth. While this is approximately how much total water the average healthy adult should consume, with mild exercise in a temperate climate, much of this intake of water is contained within our food. Additionally, other drinks, including coffee, tea, and sodas, also count towards this total water intake. Thirst is well regulated and most healthy adults will naturally consume the amount of fluids required by their body. Strenuous exercise, excessive heat or some illnesses, may cause a demand for increased water intake.^[2]

References

1. Shannon JE, et al. Relationship of Food Groups and Water Intake to Colon Cancer Risk. Cancer Epidemiol Biomarkers Prev. 1996; 5(7), 495–502. https://aacrjournals.org/cebp/article/5/7/495/154534/Relationship-of-food-groups-and-water-intake-to
2. Valtin H. ““Drink at least eight glasses of water a day.” Really? Is there scientific evidence for “8 x 8”?” Am J Physiol Regul Integr Comp Physiol. 2002; 283: R993-1004. https://doi.org/10.1152/ajpregu.00365.2002

Sodium

Sodium is vital for maintaining fluid balance. In contrast to many minerals, sodium absorption in the small intestine is extremely efficient and in a healthy individual all excess sodium is excreted by the kidneys. In fact, very little sodium is required in the diet (about 200 milligrams) because the kidneys actively reabsorb sodium. Kidney reabsorption of sodium is hormonally controlled, allowing for a relatively constant sodium concentration in the blood.

The second notable function of sodium is in nerve impulse transmission. Transport of sodium cations into a nerve cell, which creates a charge difference (or voltage) between the nerve cell and its extracellular environment, is central to neuronal cell firing as well as muscle contraction. Stimulating a muscle contraction also involves the movement of sodium ions as well as other ion movements.

Sodium is essential for nutrient absorption in the small intestine and also for nutrient reabsorption in the kidney. Amino acids, glucose and water must make their way from the small intestine to the blood. To do so, they pass through intestinal cells on their way to the blood. The transport of nutrients through intestinal cells is facilitated by the sodium-potassium pump, which by moving sodium out of the cell, creates a higher sodium concentration outside of the cell (requiring ATP).

Sodium Imbalances

Sweating is a homeostatic mechanism for maintaining body temperature, which influences fluid and electrolyte balance. Sweat is mostly water but also contains some electrolytes, mostly sodium and chloride. Under normal environmental conditions (i.e., not hot, humid days) water and sodium loss through sweat is negligible, but is highly variable among individuals. It is estimated that sixty minutes of high-intensity physical activity, like playing a game of tennis, can produce approximately one liter of sweat; however, the amount of sweat produced is highly dependent on environmental conditions. A liter of sweat typically contains between 1 and 2 grams of sodium and therefore exercising for multiple hours can result in a high amount of sodium loss in some people. Additionally, hard labor can produce substantial sodium loss through sweat. In either case, the lost sodium is easily replaced in the next snack or meal.

In athletes, hyponatremia, or a low blood-sodium level, is not so much the result of excessive sodium loss in sweat, but rather drinking too much water. The excess water dilutes the sodium concentration in blood. Illnesses causing vomiting, sweating, and diarrhea may also cause hyponatremia. The symptoms of hyponatremia, also called water intoxication (since it is often the root cause) include nausea, muscle cramps, confusion, dizziness, and in severe cases, coma and death. The physiological events that occur in water intoxication are the following:

• Excessive sodium loss and/or water intake.
• Sodium levels fall in blood and in the fluid between cells.
• Water moves to where solutes are more concentrated (i.e. into cells).
• Cells swell.
• Symptoms, including nausea, muscle cramps, confusion, dizziness, and in severe cases, coma and death result.

Hyponatremia in endurance athletes (such as marathon runners) can be avoided by drinking the correct amount of water, which is about 1 cup every twenty minutes during the event. Sports drinks are better at restoring fluid and blood-glucose levels than replacing electrolytes. During an endurance event you would be better off drinking water and eating an energy bar that contains sugars, proteins, and electrolytes. The American College of Sports Medicine suggests if you are exercising for longer than one hour you eat one high carbohydrate (25–40 grams) per hour of exercise along with ample water.^[1]

Watch out for the fat content, as sometimes energy bars contain a hefty dose. If you’re not exercising over an hour at high intensity, you can skip the sports drinks, but not the water. For those who do not exercise or do so at low to moderate intensity, sports drinks are another source of extra calories, sugar, and salt.

Needs and Dietary Sources of Sodium

The IOM has set an AI level for sodium for healthy adults between the ages of nineteen and fifty at 1,500 milligrams (Table 17.7) Table salt is approximately 40 percent sodium and 60 percent chloride. Only ⅔ teaspoon of salt is needed in the diet to meet the AI for sodium. The AI takes into account the amount of sodium lost in sweat during recommended physical activity levels and additionally provides for the sufficient intake of other nutrients, such as chloride. There is insufficient evidence of sodium toxicity within a healthy population to establish a UL in the usual manner. Rather, the association between excessive sodium intake and chronic disease risk led to the development of a Chronic Disease Risk Reduction Intake (CDRR), which is 2,300 mg/day for adults. (Just over 1 teaspoon of salt contains the 2,300 milligrams of sodium recommended). The IOM estimates that greater than 95 percent of men and 75 percent of women in America consume salt in excess of the CDRR. Many scientific studies demonstrate that reducing salt intake prevents hypertension and reduces the risk for cardiovascular disease. The IOM recommends that people over fifty, diabetics, and those with chronic kidney disease should consume no more than 1,500 milligrams of sodium per day. The American Heart Association (AHA) states that all Americans, not just those listed, should consume less than 1,500 milligrams of sodium per day to prevent cardiovascular disease.

Table 17.7 Dietary Reference Intakes for Sodium. Source: National Academy of Sciences, Engineering, and Medicine. Dietary Reference Intakes for Sodium and Potassium. 2019. Washington DC: The National Academies Press. Used under fair use guidelines.

Age Group	AI (mg/day)	CDRR (mg/day)
Infants (0–6 months)	120	Not determined
Infants (6–12 months)	370	Not determined
Children (1–3 years)	800	1,200
Children (4–8 years)	1,000	1,500
Children (9–13 years)	1,200	1,800
Adolescents and Adults (14+)	1,500	2,300

Food Sources for Sodium

Most sodium in the typical American diet comes from processed and prepared foods. Manufacturers add salt to foods to improve texture and flavor, and also as a preservative. The amount of salt in similar food products varies widely. Some foods, such as meat, poultry, and dairy foods, contain naturally-occurring sodium. For example, one cup of low-fat milk contains 107 milligrams of sodium. Naturally-occurring sodium accounts for less than 12 percent of dietary intake in a typical diet.

 

Table 17.8 Sodium Contents of Selected Foods. 

Food Group	Serving Size	Sodium (mg)
Breads, all types	1 oz.	95–210
Raisin Bran cereal	1 c.	362
Frozen pizza, plain, cheese	4 oz.	450–1200
Frozen vegetables, all types	½ c.	2–160
Salad dressing, regular fat, all types	2 Tbsp.	110–505
Salsa	2 Tbsp.	150–240
Soup (tomato), reconstituted	8 oz.	700–1260
Potato chips	1 oz. (28.4 g)	120–180
Tortilla chips	1 oz. (28.4 g)	105–160
Pork	3 oz.	59
Chicken	(½ breast)	69
Chicken fast food dinner		2243
Dill pickle	1	928
Soy sauce	1 Tbsp.	1029
Canned corn	1 c.	384
Baked beans, canned	1 c.	856
Hot dog	1	639
Burger, fast-food	1	990
Steak	3 oz.	55
Canned tuna	3 oz.	384
Fresh tuna	3 oz.	50
Dry-roasted peanuts	1 c.	986
American cheese	1 oz.	406
Tap water	8 oz.	12

Sodium on the Nutrition Facts Panel

The Nutrition Facts panel displays the amount of sodium (in milligrams) per serving of the food in question (Figure 17.8). Food additives are often high in sodium; for example, monosodium glutamate (MSG) contains 12 percent sodium. Additionally, baking soda, baking powder, disodium phosphate, sodium alginate, and sodium nitrate or nitrite contain a significant proportion of sodium as well. When you see a food’s Nutrition Facts label, you can check the ingredients list to identify the source of the added sodium. Various claims about the sodium content in foods must be in accordance with Food and Drug Administration (FDA) regulations (Table 17.9).

 

Table 17.9 Food Packaging Claims Regarding Sodium. Source: Food Labeling Guide. US Food and Drug Administration. January 2013. Public domain.

Claim	Meaning
“Light in Sodium”	Sodium reduced by at least 50 percent vs. reference food
“No Salt Added” or “Unsalted”	No salt added during preparation and processing (Must also declare on package “This is not a sodium-free food” if food is not sodium-free)
“Lightly Salted”	50 percent less sodium than that added to reference food
“Sodium Free” or “Salt Free”	Contains less than 5 mg sodium per serving
“Very Low Sodium”	Contains less than 35 mg sodium per serving
“Low Sodium”	Contains less than 140 mg sodium per serving

Salt Substitutes

For those with hypertension or those looking for a way to decrease salt use, using a salt substitute for food preparation is one option. However, many salt substitutes still contain sodium, just in lesser amounts than table salt. Also, remember that most salt in the diet is not from table-salt use, but from processed foods. Salt substitutes often replace the sodium with potassium. People with kidney disorders often have problems getting rid of excess potassium in the diet and are advised to avoid salt substitutes containing potassium. People with liver disorders should also avoid salt substitutes containing potassium because their treatment is often accompanied by potassium dysregulation.

References

1. Convertino VA, et al. American College of Sports Medicine Position Stand. Exercise and Fluid Replacement. Medicine and Science in Sports and Exercise. 1996; 28(1) i–vii. https://doi.org/10.1097/00005768-199610000-00045.  

Potassium

Potassium is the most abundant positively charged ion inside of cells. Ninety percent of potassium exists in intracellular fluid, with about 10 percent in extracellular fluid, and only 1 percent in blood plasma. As with sodium, potassium levels in the blood are strictly regulated. The hormone aldosterone is what primarily controls potassium levels, but other hormones also play a role. When potassium levels in the blood increase, the adrenal glands release aldosterone. The aldosterone acts on the collecting ducts of kidneys, where it stimulates an increase in the number of sodium-potassium pumps. Sodium is then reabsorbed and more potassium is excreted. Because potassium is required for maintaining sodium levels, and hence fluid balance, about 200 milligrams of potassium are lost from the body every day.

Other Functions of Potassium in the Body

Nerve impulse involves not only sodium, but also potassium. A nerve impulse moves along a nerve via the movement of sodium ions into the cell. To end the impulse, potassium ions rush out of the nerve cell, thereby decreasing the positive charge inside the nerve cell. This diminishes the stimulus. To restore the original concentrations of ions between the intracellular and extracellular fluid, the sodium-potassium pump transfers sodium ions out in exchange for potassium ions in. On completion of the restored ion concentrations, a nerve cell is now ready to receive the next impulse. Similarly, in muscle cells potassium is involved in restoring the normal membrane potential and ending the muscle contraction. Potassium also is involved in protein synthesis, energy metabolism, and platelet function, and acts as a buffer in blood, playing a role in acid-base balance.

Imbalances of Potassium

Insufficient potassium levels in the body (hypokalemia) can be caused by a low dietary intake of potassium or by high sodium intakes, but more commonly it results from medications that increase water excretion, mainly diuretics. The signs and symptoms of hypokalemia are related to the functions of potassium in nerve cells and consequently skeletal and smooth-muscle contraction. The signs and symptoms include muscle weakness and cramps, respiratory distress, and constipation. Severe potassium depletion can cause the heart to have abnormal contractions and can even be fatal. High levels of potassium in the blood, or hyperkalemia, also affects the heart. It is a silent condition as it often displays no signs or symptoms. Extremely high levels of potassium in the blood disrupt the electrical impulses that stimulate the heart and can cause the heart to stop. Hyperkalemia is usually the result of kidney dysfunction.

Needs and Dietary Sources of Potassium

The IOM based their AIs for potassium on the levels associated with a decrease in blood pressure, a reduction in salt sensitivity, and a minimal risk of kidney stones. No ULs for potassium have been established, as research has not found significant reason for concern of toxicity.

Table 17.10 Adequate Intakes for Potassium. Source: National Academy of Sciences, Engineering, and Medicine. Dietary Reference Intakes for Sodium and Potassium. 2019. Washington DC: The National Academies Press. Used under fair use guidelines.

Age Group	AI (mg/day)
Infants (0–6 months)	400
Infants (6–12 months)	860
Children (1–3 years)	2,000
Children (4–8 years)	2,300
Children (9–13 years)	2,500 (males), 2,300 (females)
Adolescents (14–18 years)	3,000 (males), 2,300 (females)
Adults (> 19 years)	3,400 (males), 2,600 (females)

Fruits and vegetables that contain high amounts of potassium are spinach, lettuce, broccoli, peas, tomatoes, potatoes, bananas, apples and apricots. Whole grains and seeds, certain fish (such as salmon, cod, and flounder), and meats are also high in potassium. The Dietary Approaches to Stop Hypertension (DASH diet) emphasizes potassium-rich foods and will be discussed in greater detail in a later section.

Bioavailability

Greater than 90 percent of dietary potassium is absorbed in the small intestine. Although highly bioavailable, potassium is a very soluble mineral and easily lost during cooking and processing of foods. Fresh and frozen foods are better sources of potassium than canned.

Chloride

Chloride is the primary anion in extracellular fluid. In addition to passively following sodium, chloride has its own protein channels that reside in cell membranes. These protein channels are especially abundant in the gastrointestinal tract, pancreas, and lungs.

Chloride’s Role in Fluid Balance

Chloride aids in fluid balance mainly because it follows sodium in order to maintain charge neutrality. Chloride channels also play a role in regulating fluid secretion, such as pancreatic juice into the small intestine and the flow of water into mucus. Fluid secretion and mucus are important for many of life’s processes. Their importance is exemplified in the signs and symptoms of the genetic disease, cystic fibrosis.

Cystic Fibrosis

Cystic fibrosis (CF) is one of the most prevalent inherited diseases in people of European descent. It is caused by a mutation in a protein that transports chloride ions out of the cell. CF’s signs and symptoms include salty skin, poor digestion and absorption (leading to poor growth), sticky mucus accumulation in the lungs (causing increased susceptibility to respiratory infections), liver damage, and infertility.

Other Functions of Chloride

Chloride has several other functions in the body, most importantly in acid-base balance. Blood pH is maintained in a narrow range and the number of positively charged substances is equal to the number of negatively charged substances. Proteins, such as albumin, as well as bicarbonate ions and chloride ions, are negatively charged and aid in maintaining blood pH. Hydrochloric acid (a gastric acid composed of chlorine and hydrogen) aids in digestion and also prevents the growth of unwanted microbes in the stomach. Immune-system cells require chloride, and red blood cells use chloride anions to remove carbon dioxide from the body.

Chloride Imbalances

Low dietary intake of chloride and more often diarrhea can cause low blood levels of chloride. Symptoms typically are similar to those of hyponatremia and include weakness, nausea, and headache. Excess chloride in the blood is rare with no characteristic signs or symptoms.

Needs and Dietary Sources of Chloride

Most chloride in the diet comes from salt. (Salt is 60 percent chloride.) A teaspoon of salt equals 5,600 milligrams, with each teaspoon of salt containing 3,400 milligrams of chloride and 2,200 milligrams of sodium. The chloride AI for adults, set by the IOM, is 2,300 milligrams. Therefore, just ⅔ teaspoon of table salt per day is sufficient for chloride as well as sodium. The AIs for other age groups are listed in Table 17.11.

Table 17.11 Adequate Intakes for Chloride. Source: Institute of Medicine. Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate. 2005. Washington, DC: The National Academies Press. Used under fair use guidelines.

Age Group	AI (mg/day)
Infants (0–6 months)	180
Infants (6–12 months)	570
Children (1–3 years)	1,500
Children (4–8 years)	1,900
Children (9–13 years)	2,300
Adolescents (14–18 years)	2,300
Adults (19–50 years)	2,300
Adults (51–70 years)	2,000
Adults (> 70 years)	1,800

Chloride has dietary sources other than table salt, namely as another form of salt—potassium chloride. Dietary sources of chloride are: all foods containing sodium chloride, as well as tomatoes, lettuce, olives, celery, rye, whole-grain foods, and seafood. Although many salt substitutes are sodium-free, they may still contain chloride.

Bioavailability

Bioavailability refers to the amount of a particular nutrient in foods that is actually absorbed in the intestine and not eliminated in the urine or feces. Simply put, the bioavailability of chloride is the amount that is on hand to perform its biological functions. In the small intestine, the elements of sodium chloride split into sodium cations and chloride anions. Chloride follows the sodium ion into intestinal cells passively, making chloride absorption quite efficient. When chloride exists as a potassium salt, it is also well absorbed. Other mineral salts, such as magnesium chloride, are not absorbed as well, but bioavailability still remains high.

Sodium and Hypertension

Blood pressure is the force of moving blood against arterial walls. It is reported as the systolic pressure over the diastolic pressure, which is the greatest and least pressure on an artery that occurs with each heartbeat. The force of blood against an artery is measured with a device called a sphygmomanometer. The results are recorded in millimeters of mercury, or mmHg. A desirable blood pressure ranges between 90/60 and 120/80 mmHg. Hypertension is the scientific term for high blood pressure and defined as a sustained blood pressure of 140/90 mmHg or greater. Hypertension is a risk factor for cardiovascular disease, and reducing blood pressure has been found to decrease the risk of dying from a heart attack or stroke. The Centers for Disease Control and Prevention (CDC) reported that in 2017-2020 approximately 48 percent of American adults were hypertensive.^[1]

There has been much debate about the role sodium plays in hypertension. In the latter 1980s and early 1990s the largest epidemiological study evaluating the relationship of dietary sodium intake with blood pressure, called INTERSALT, was completed and then went through further analyses.^{[2, 3]}

More than ten thousand men and women from thirty-two countries participated in the study. The study concluded that a higher sodium intake is linked to an increase in blood pressure. A more recent study, involving over twelve thousand US citizens, concluded that a higher sodium-to-potassium intake is linked to higher cardiovascular mortality and all-causes mortality.^[4]

The DASH-Sodium trial was a clinical trial which evaluated the effects of a specified eating plan with or without reduced sodium intake. The DASH diet is an eating plan that is low in saturated fat, cholesterol, and total fat. Fruits, vegetables, low-fat dairy foods, whole-grain foods, fish, poultry, and nuts are emphasized while red meats, sweets, and sugar-containing beverages are mostly avoided. In this study, people on the low-sodium (1500 milligrams per day) DASH diet had mean systolic blood pressures that were 7.1 mmHg lower than people without hypertension not on the DASH diet. The effect on blood pressure was greatest in participants with hypertension at the beginning of the study who followed the DASH diet. Their systolic blood pressures were, on average, 11.5 mmHg lower than participants with hypertension on the control diet.^[5]

Following the DASH diet not only reduces sodium intake, but also increases potassium, calcium, and magnesium intake. All of these electrolytes have a positive effect on blood pressure, although the mechanisms by which they reduce blood pressure are largely unknown.

While some other large studies have demonstrated little or no significant relationship between sodium intake and blood pressure, the weight of scientific evidence demonstrating low-sodium diets as effective preventative and treatment measures against hypertension led the US government to pass a focus on salt within the Consolidated Appropriations Act of 2008. A part of this act tasked the CDC, under guidance from the IOM, to make recommendations for Americans to reduce dietary sodium intake. This task is ongoing and involves “studying government approaches (regulatory and legislative actions), food supply approaches (new product development, food reformulation), and information/education strategies for the public and professionals.”^[6]

Salt Sensitivity

High dietary intake of sodium is one risk factor for hypertension and contributes to high blood pressure in many people. However, studies have shown that not everyone’s blood pressure is affected by lowering sodium intake. Estimates vary, though some portion (10-30%, depending on the source) of the population is considered to be salt-sensitive, meaning their blood pressure is affected by salt intake. Genetics, race, gender, weight, and physical activity level are determinants of salt sensitivity. African Americans, women, and overweight individuals are more salt-sensitive than others. Also, if hypertension runs in a person’s family, that person is more likely to be salt-sensitive.

References

1. Centers for Disease Control and Prevention. “High Blood Pressure Facts.” https://www.cdc.gov/high-blood-pressure/data-research/facts-stats/index.html Updated January 28, 2025. Accessed March 3, 2026.
2. Intersalt Cooperative Research Group. Intersalt: An International Study of Electrolyte Excretion and Blood Pressure. Results for 24 Hour Urinary Sodium and Potassium Excretion. BMJ. 1988; 297(6644), 319–28. https://doi.org/10.1136/bmj.297.6644.319.
3. Elliott P, Stamler J, et al. Intersalt Revisited: Further Analyses of 24 Hour Sodium Excretion and Blood Pressure within and across Populations. BMJ. 1996; 312(7041), 1249–53. https://doi.org/10.1136/bmj.312.7041.1249
4. Yang Q, Liu T, et al. Sodium and Potassium Intake and Mortality among US Adults: Prospective Data from the Third National Health and Nutrition Examination Survey. Arch Intern Med. 2011; 171(13), 1183–91. https://doi.org/10.1001/archinternmed.2011.257.
5. Sacks, FM, Svetkey LP, et al. Effects on Blood Pressure of Reduced Dietary Sodium and the Dietary Approaches to Stop Hypertension (DASH) Diet. N Engl J Med. 2001; 344(1), 3–10. https://doi.org/10.1056/nejm200101043440101.
6. Institute of Medicine. Strategies to Reduce Sodium Intake in the United States. 2010. Washington, D.C.: National Academies Press. https://doi.org/10.17226/12818.

Minerals and Blood Cell Function

The mineral iron is an integral component of heme, a structural part of a protein that has a complexed iron cation. Heme groups are essential for oxygen transport by red blood cells, but is also important in many other metabolic reactions. For example, heme groups are also central to the ability of phagocytic white blood cells to kill pathogens. Copper and zinc are two minerals that also play important roles in blood cell function by their important roles in iron absorption and transport and the synthesis of heme groups.

Iron

Red blood cells contain the oxygen-carrier protein hemoglobin. It is composed of four globular peptides, each containing a heme complex. In the center of each heme, lies iron (Figure 17.9). Iron is needed for the production of other iron-containing proteins such as myoglobin. Myoglobin is a protein found in the muscle tissues that enhances the amount of available oxygen for muscle contraction.

Iron is also a key component of hundreds of metabolic enzymes. Many of the proteins of the electron-transport chain contain iron–sulfur clusters involved in the transfer of high-energy electrons and ultimately ATP synthesis. Iron is also involved in numerous metabolic reactions that take place mainly in the liver and detoxify harmful substances. Moreover, iron is required for DNA synthesis.

Iron Bioavailability

The bioavailability of iron is highly dependent on dietary sources. In animal-based foods about 60 percent of iron is bound to hemoglobin, and heme iron is more bioavailable than nonheme iron. The other 40 percent of iron in animal-based foods is nonheme, which is the only iron source in plant-based foods. Some plants contain chemicals (such as phytate, oxalates, tannins, and polyphenols) that inhibit iron absorption. On the other hand, eating fruits and vegetables rich in vitamin C at the same time as iron-containing foods markedly increases iron absorption. Vegans are at higher risk for iron deficiency, but careful meal planning does prevent its development. Iron deficiency is the most common of all micronutrient deficiencies. A list of enhancers and inhibitors of iron absorption follows:

• Enhancers
  • Meat factor (found in meat and fish)
  • Sufficient stomach acid
  • Vitamin C
• Inhibitors
  • Calcium
  • Antacids
  • Phytates (found in beans, rice, whole grains)
  • Oxalates (found in dark leafy greens, some nuts, beans)
  • Polyphenols (found in chocolate, wine, tea, coffee, oregano)
  • Soybean protein

Iron Homeostasis

The body tightly regulates iron absorption, transport and storage. As free iron in our body can be toxic, iron is nearly always bound tightly to proteins. Heme groups such as that found in hemoglobin or myoglobin is one option. For blood transport, iron is oxidized to Fe³⁺ by ceruloplasmin and then the ferric iron is transported by transferrin. Iron can also be stored as ferritin or hemosiderin. Iron stores are found in the bone marrow, spleen and liver. Iron in the body is heavily recycled with breakdown of either hemoglobin or myoglobin regulated and the iron content recycled by the spleen or liver. Uptake of iron in the diet is inhibited as iron levels in the body increase. This change in uptake is mediated by a hormone called hepcidin.

Iron Toxicity

The body excretes little iron and therefore the potential for accumulation in tissues and organs is considerable. Iron accumulation can cause a host of health problems in children and adults including extreme fatigue, arthritis, joint pain, and severe liver and heart toxicity. In children, death has occurred from ingesting as little as 200 mg of iron and therefore it is critical to keep iron supplements out of children’s reach. The IOM has set tolerable upper intake levels of iron (Table 17.14). Mostly a hereditary disease, hemochromatosis is the result of a genetic mutation that leads to abnormal iron metabolism and an accumulation of iron in certain tissues such as the liver, pancreas, and heart. The signs and symptoms of hemochromatosis are similar to those of iron overload in tissues caused by high dietary intake of iron or other non-genetic metabolic abnormalities, but are often increased in severity.

Dietary Reference Intakes for Iron

Table 17.12 Dietary Reference Intakes for Iron. Source: Iron – Health Professional Fact Sheet. National Institutes of Health, Office of Dietary Supplements. Updated October 9, 2024. Accessed August 28, 2025. Public domain.

Age Group	RDA (or AI*) (mg/day)	UL (mg/day)
Infant (0–6 months)	0.27*	40
Infants (6–12 months)	11*	40
Children (1–3 years)	7	40
Children (4–8 years)	10	40
Children (9–13 years)	8	40
Adolescents (14–18 years)	11 (males), 15 (females)	45
Adults (19–50 years)	8 (males), 18 (females)	45
Adults (> 50 years)	8	45

Dietary Sources of Iron

Table 17.13 Iron Content of Various Foods. Source: Iron – Health Professional Fact Sheet. National Institutes of Health, Office of Dietary Supplements. Updated October 9, 2024. Accessed March 3, 2026. Public domain.

Food	Serving	Iron (mg)	Percent Daily Value
Breakfast cereals, fortified	1 serving	18	100
Oysters	3 oz.	8	44
Dark chocolate	3 oz.	7	39
Beef liver	3 oz.	5	28
Lentils	½ c.	3	17
Spinach, boiled	½ c.	3	17
Tofu, firm	½ c.	3	17
Kidney beans	½ c.	2	11
Sardines	3 oz.	2	11

Iron-Deficiency Anemia

Iron-deficiency anemia is a condition that develops from having insufficient iron levels in the body resulting in fewer and smaller red blood cells containing lower amounts of hemoglobin, a type of microcytic anemia. Regardless of the cause (be it from low dietary intake of iron or via excessive blood loss), iron-deficiency anemia has the following signs and symptoms, which are linked to the essential functions of iron in energy metabolism and blood health:

• Fatigue
• Weakness
• Pale skin
• Shortness of breath
• Dizziness
• Swollen, sore tongue
• Abnormal heart rate

Iron-deficiency anemia is diagnosed from characteristic signs and symptoms and confirmed with simple blood tests that count red blood cells and determine hemoglobin and iron content in blood. Anemia is most often treated with iron supplements and increasing the consumption of foods that are higher in iron. Iron supplements have some adverse side effects including nausea, constipation, diarrhea, vomiting, and abdominal pain. Reducing the dose at first and then gradually increasing to the full dose often minimizes the side effects of iron supplements. Avoiding foods and beverages high in phytates and also tea (which contains tannic acid and polyphenols, both of which impair iron absorption), is important for people who have iron-deficiency anemia. Eating a dietary source of vitamin C at the same time as iron-containing foods improves absorption of nonheme iron in the gut. Additionally, unknown compounds that likely reside in muscle tissue of meat, poultry, and fish increase iron absorption from both heme and nonheme sources.

Iron Deficiency: A Worldwide Nutritional Health Problem

Iron deficiency, a leading cause of anemia, is a global problem. Many people in the US get sufficient iron, though this varies by race and other demographic factors. About 23% of US females aged 12 to 49 years were found to have iron deficiency in the years 2017-2020 [1]. Pregnancy depletes iron stores; in the US, different groups of pregnant people experience iron deficiency at rates from 14% to 30%.^[2] Causes of iron deficiency include dietary insufficiency and parasitic worm infection, among others.

Infants, children, adolescents, and women are the populations most at risk worldwide for iron-deficiency anemia by all causes. Infants, children, and even teens require more iron because iron is essential for growth. In these populations, iron deficiency can also cause the following signs and symptoms: poor growth, failure to thrive, and poor performance in school, as well as mental, motor, and behavioral disorders. Women who experience heavy menstrual bleeding or who are pregnant require more iron in the diet. One more high-risk group is the elderly. Both elderly men and women have a high incidence of anemia and the most common causes are dietary iron deficiency and chronic disease such as ulcer, inflammatory diseases, and cancer. Additionally, those who have recently suffered from traumatic blood loss, frequently donate blood, or take excessive antacids for heartburn need more iron in the diet.

Preventing Iron-Deficiency Anemia

In young children iron-deficiency anemia can cause significant motor, mental, and behavioral abnormalities that are long-lasting. In the United States, the high incidence of iron-deficiency anemia in infants and children was a major public-health problem prior to the early 1970s, but now the incidence has been greatly reduced. This achievement was accomplished by implementing the screening of infants for iron-deficiency anemia in the health sector as a common practice, advocating the fortification of infant formulas and cereals with iron, and distributing them in supplemental food programs, such as that within Women, Infants, and Children (WIC). Breastfeeding, iron supplementation, and delaying the introduction of cow’s milk for at least the first twelve months of life were also encouraged. These practices were implemented across the socioeconomic spectrum and by the 1980s iron-deficiency anemia in infants had significantly declined. Other solutions had to be introduced in young children, who no longer were fed breast milk or fortified formulas and were consuming cow’s milk. The following solutions were introduced to parents: provide a diet rich in sources of iron and vitamin C, limit cow’s milk consumption to less than twenty-four ounces per day, and a multivitamin containing iron.

References

1. Anemia or Iron Deficiency. National Center for Health Statistics, Centers for Disease Control and Prevention. https://www.cdc.gov/nchs/fastats/anemia.htm Updated January 23, 2026. Accessed March 3, 2026.
2. Iron – Health Professional Fact Sheet. National Institutes of Health, Office of Dietary Supplements. https://ods.od.nih.gov/factsheets/Iron-HealthProfessional/. Updated October 9, 2024. Accessed March 3, 2026.

Copper

Copper has a number of roles in the body. Copper is an important cofactor for many enzymes. Like iron, the copper complexes are important in the proteins of the electron-transport chain. The other important function of copper is as part of an enzyme called superoxide dismutase which is important in protecting our cells from oxidant damage. Most copper in the blood is part of an enzyme called ceruloplasmin. This enzyme is critical in iron homeostasis as it oxidizes ferrous (Fe²⁺) to ferric (Fe³⁺) iron, allowing iron to be transported by transferrin. Additionally, copper-containing enzymes also play roles in neurotransmitter synthesis, myelin production, and angiogenesis.

Similar to iron, copper is generally protein-bound in the body as free iron can be toxic meaning that its absorption, transport and elimination uses proteins. Unlike iron, there are limited stores of copper in the body.

Symptoms of mild to moderate copper deficiency are rare and are generally related to its effects on iron. More severe copper deficiency can cause anemia from the lack of iron mobilization in the body for red blood cell synthesis. Other signs and symptoms include growth retardation in children and neurological problems, because copper is a cofactor for an enzyme that synthesizes myelin, which surrounds many nerves.

Dietary Reference Intakes for Copper

While copper deficiency is rare, individuals at risk include those with celiac disease, Menkes disease, or patients taking large amounts of zinc supplements.

Table 17.14 Dietary Reference Intakes for Copper. Source: Source: Copper – Health Professional Fact Sheet. National Institutes of Health, Office of Dietary Supplements. Updated October 18, 2022. Accessed August 28, 2025. Public domain.

Age Group	RDA (or AI*) (µg/day)	UL (µg/day)
Infant (0–6 months)	200*	Not established
Infants (6–12 months)	220*	Not established
Children (1–3 years)	340	1,000
Children (4–8 years)	440	3,000
Children (9–13 years)	700	5,000
Adolescents (14–18 years)	890	8,000
Adults (19– years)	900	10,000

Dietary Sources of Copper

A wide variety of plant and animal foods contain copper with richest sources being shellfish, seeds and nuts, organ meats, and chocolate.

Table 17.15 Dietary Sources of Copper. Source: Copper – Health Professional Fact Sheet. National Institutes of Health, Office of Dietary Supplements. Updated October 18, 2022. Accessed March 3, 2026. Public domain.

Food	Serving Size	Copper (µg)	% Daily Value
Beef liver	3 oz.	12,400	1378
Oysters	3 oz.	4,850	539
Unsweetened chocolate	1 oz.	938	104
Cashews, dry roasted	1 oz.	629	70
Millet, cooked	1 c.	280	31
Avocado	½ c.	219	24
Tomatoes, raw	½ c.	53	6

Zinc

Zinc is a cofactor for over two hundred enzymes in the human body and plays a direct role in RNA, DNA, and protein synthesis. Zinc also is a cofactor for enzymes involved in energy metabolism. As the result of its prominent roles in anabolic and energy metabolism, a zinc deficiency in infants and children blunts growth. The reliance of growth on adequate dietary zinc was discovered in the early 1960s in the Middle East where adolescent nutritional dwarfism was linked to diets containing high amounts of phytate. Cereal grains and some vegetables contain chemicals, one being phytate, which blocks the absorption of zinc and other minerals in the gut. It is estimated that about 17% of the world’s population is at risk of inadequate zinc intake.^[1]

This is largely a consequence of the lack of red meat and seafood in the diet and reliance on cereal grains as the main dietary staple. In adults, severe zinc deficiency can cause hair loss, diarrhea, skin sores, loss of appetite, and weight loss. Zinc is a required cofactor for an enzyme that synthesizes the heme portion of hemoglobin and severely deficient zinc diets can result in anemia.

Zinc toxicity can be associated with zinc supplementation. Acute effects include nausea, vomiting, diarrhea, loss of appetite, and headaches. Chronically high levels can lead to exhaustion, reduced levels of iron and copper, and reduced HDL levels in blood.

There has been research into a link between zinc intake and the common cold. Data from clinical trials show mixed results, with some encouraging results being seen with lozenges and thick syrups and taking the supplements within 24 h of symptom onset. However, more research is needed to determine the best dose, formulation and duration of treatment.^[2]

Dietary Reference Intakes for Zinc

Table 17.16 Dietary Reference Intakes for Zinc. Source: Zinc – Health Professional Fact Sheet. National Institutes of Health, Office of Dietary Supplements. Updated September 28, 2022. Accessed August 29, 2025. Public domain.

Age Group	RDA (or AI*) (mg/day)	UL (mg/day)
Infant (0–6 months)	2*	4
Infants (7–12 months)	3	5
Children (1–3 years)	3	7
Children (4–8 years)	5	12
Children (9–13 years)	8	23
Adolescents (14–18 years)	11 (males), 9 (females)	34
Adults (19 + years)	11 (males), 8 (females)	40

Dietary Sources of Zinc

Table 17.17 Zinc Content of Various Foods. Source: Zinc – Health Professional Fact Sheet. National Institutes of Health, Office of Dietary Supplements. Updated September 28, 2022. Accessed March 3, 2026. Public domain.

Food	Serving	Zinc (mg)	Percent Daily Value
Oysters, cooked	3 oz.	28.2	256
Beef, sirloin	3 oz.	3.8	35
Blue crab, cooked	3 oz.	3.2	29
Pumpkin seeds, roasted	1 oz.	2.2	20
Pork loin	3 oz.	1.9	17
Lentils, boiled	½ c.	1.3	12
Rice, brown	½ c.	0.7	6
Blueberries, raw	½ c.	0.1	1

References

1. Lowe NM et al.  Preventing and Controlling Zinc Deficiency Across the Life Course: A Call to Action. Advances in Nutrition. 2024; 100181. https://doi.org/10.1016/j.advnut.2024.100181
2. Hulisz D. Efficacy of zinc against common cold viruses: an overview. J Am Pharm Assoc (2003) 2004; 44:594-603. https://doi.org/10.1331/1544-3191.44.5.594.hulisz.

Iodine and Metabolism

Dietary iodine is required for the synthesis of thyroid hormones by the thyroid gland located in the neck. The thyroid hormones, T₃ and T₄, are often referred to as metabolic hormones because their levels influence the body’s basal metabolic rate, the amount of energy used by the body at rest. When T₃ and T₄ bind to intracellular receptors located on the mitochondria, they cause an increase in nutrient breakdown and the use of oxygen to produce ATP. In addition, T₃ and T₄ initiate the transcription of genes involved in glucose oxidation. Although these mechanisms prompt cells to produce more ATP, the process is inefficient, and an abnormally increased level of heat is released as a byproduct of these reactions. This so-called calorigenic effect (calor– = “heat”) raises body temperature.

Adequate levels of thyroid hormones are also required for protein synthesis and for fetal and childhood tissue development and growth. They are especially critical for normal development of the nervous system both in utero and in early childhood, and they continue to support neurological function in adults. As noted earlier, these thyroid hormones have a complex interrelationship with reproductive hormones, and deficiencies can influence libido, fertility, and other aspects of reproductive function. Finally, thyroid hormones increase the body’s sensitivity to catecholamines (epinephrine and norepinephrine) from the adrenal medulla by upregulation of receptors in the blood vessels. When levels of T₃ and T₄ hormones are excessive, this effect accelerates the heart rate, strengthens the heartbeat, and increases blood pressure. Because thyroid hormones regulate metabolism, heat production, protein synthesis, and many other body functions, thyroid disorders can have severe and widespread consequences.

For much of the world’s population, foods do not provide adequate levels of this mineral, because the amount varies according to the level in the soil in which the food was grown. Marine fish and shrimp tend to have high levels because they concentrate iodine from seawater, but many people in landlocked regions lack access to seafood. Thus, the primary source of dietary iodine in many countries is iodized salt. Fortification of salt with iodine began in the United States in 1924, and international efforts to iodize salt in the world’s poorest nations continue today. In 2004, the World Health Organization (WHO) estimated that iodine deficiency affects over two billion people worldwide, and it is the number-one cause of preventable intellectual disability worldwide.^[1]

Dietary iodine deficiency can result in the impaired ability to synthesize thyroid hormone, leading to a variety of severe disorders. When thyroid hormones cannot be produced, Thyroid Stimulating Hormone is secreted in increasing amounts. As a result of this hyperstimulation, the thyroid gland increases in size, a condition called a goiter. A goiter is only a visible indication of the deficiency. Normally, a hormone from the pituitary gland, TSH, tells the thyroid gland to make thyroid hormones. Once the thyroid hormones are made, they cause a reduction of TSH secretion so excess thyroid hormone does not get made.

If thyroid hormone cannot be produced, the TSH is constantly stimulating the thyroid telling it to make more thyroid hormones. This causes the gland to grow creating a goiter. Goiter is easily reversible with iodine supplementation. Ancients medical texts from China, Egypt and Rome all describe such treatment using sea weed or sea sponges.

Other iodine deficiency disorders include impaired growth and development, decreased fertility, and prenatal and infant death. Moreover, thyroid hormone plays a major role in brain development and growth and fetuses and infants with severe iodine deficiency develop a condition known as cretinism, in which physical and neurological impairment can be severe. Neonatal hypothyroidism (cretinism) is characterized by cognitive deficits, short stature, and sometimes deafness and muteness in children and adults born to mothers who were iodine-deficient during pregnancy.

Dietary Reference Intakes for Iodine

Table 17.18 Dietary Reference Intakes for Iodine. Source: Iodine – Health Professional Fact Sheet. National Institutes of Health, Office of Dietary Supplements. Updated November 5, 2024. Accessed August 29, 2025. Public domain.

Age Group	RDA (or AI*) (µg/day)	UL (µg/day)
Infants (0–6 months)	110*	Not established
Infants (7–12 months)	130*	Not established
Children (1–3 years)	90	200
Children (4–8 years)	90	300
Children (9–13 years)	120	600
Adolescents (14–18 years)	150	900
Adults (> 19 years)	150	1,100

Dietary Sources of Iodine

The mineral content of foods is greatly affected by the soil from which it grew, and thus geographic location is the primary determinant of the mineral content of foods. Most of the world’s iodine is in seawater. In general, the greater the distance from the sea the lesser the iodine content in the soil. However, past geological evens have sometimes led to iodine leaching from even coastal soils. Amount of iodine will vary greatly in non-ocean food sources.

Table 17.19 Iodine Content of Various Foods. Source: Iodine – Health Professional Fact Sheet. National Institutes of Health, Office of Dietary Supplements. Updated November 5, 2024. Accessed March 3, 2026. Public domain.

Food	Serving	Iodine (µg)	Percent Daily Value
Cod fish, baked	3 oz.	146	97
Dried seaweed, nori, flaked	5 g	116	77
Yogurt, nonfat	¾ c.	87	58
Iodized salt	¼ tsp.	78	52
Egg, hard boiled	1 large	31	21
Ice cream, chocolate	2/3 c.	28	19
Tuna, canned	3 oz.	7	5
Fruit cocktail, light syrup, canned	½ c.	5	3
Apple juice	1 c.	1	1

References

1. World Health Organization. “Iodine Status Worldwide.” 2004. https://www.who.int/publications/i/item/9241592001.  

Antioxidant Minerals

Selenium

Selenium is a cofactor of enzymes that release active thyroid hormone in cells and therefore low levels can cause similar signs and symptoms as iodine deficiency. The other important function of selenium is as an antioxidant.

Around twenty-five known proteins require selenium to function. Some are enzymes involved in detoxifying free radicals and include glutathione peroxidases and thioredoxin reductase. As an integral functioning part of these enzymes, selenium aids in the regeneration of glutathione and oxidized vitamin C. Selenium as part of glutathione peroxidase also protects lipids from free radicals, and, in doing so, spares vitamin E. This is just one example of how antioxidants work together to protect the body against free-radical induced damage. Other functions of selenium-containing proteins include protecting endothelial cells that line tissues, converting the inactive thyroid hormone to the active form in cells, and mediating inflammatory and immune system responses.

Observational studies have demonstrated that selenium deficiency is linked to an increased risk of cancer. A review of of randomized controlled trials and observational studies published in the Cochrane Database of Systematic Reviews, updated in 2018, concluded that there currently is no convincing evidence that selenium supplements reduce cancer risk. Collectively, the studies present conflicting evidence and suffer from several limitations.^[1]

Because of its role as a lipid protector, selenium has been suspected to prevent cardiovascular disease. In some observational studies, low levels of selenium are associated with a decreased risk of cardiovascular disease. However, other studies have not always confirmed this association and clinical trials are lacking.

Dietary Reference Intakes for Selenium

The IOM has set the RDAs for selenium based on the amount required to maximize the activity of glutathione peroxidases found in blood plasma.

Table 17.20 Dietary Reference Intakes for Selenium. Source: Selenium – Health Professional Fact Sheet. National Institutes of Health, Office of Dietary Supplements. Updated April 15, 2024. Accessed August 29, 2025. Public domain.

Age Group	RDA (or AI*) (µg/day)	UL(µg/day)
Infants (0–6 months)	15*	45
Infants (7–12 months)	20*	60
Children (1–3 years)	20	90
Children (4–8 years)	30	150
Children (9–13 years)	40	280
Adolescents (14–18 years)	55	400
Adults (> 19 years)	55	400

Selenium at doses several thousand times the RDA can cause acute toxicity, and when ingested in gram quantities can be fatal. Chronic exposure to foods grown in soils containing high levels of selenium (significantly above the UL) can cause brittle hair and nails, gastrointestinal discomfort, skin rashes, halitosis, fatigue, and irritability. The IOM has set the UL for selenium for adults at 400 micrograms per day.

Dietary Sources of Selenium

Organ meats, muscle meats, and seafood have the highest selenium content. Plants do not require selenium, so the selenium content in fruits and vegetables is usually low and varies greatly with the selenium content of the soil in which they are grown. Animals fed grains from selenium-rich soils do contain some selenium. Grains and some nuts contain selenium when grown in selenium-containing soils.

Table 17.21 Selenium Contents of Various Foods. Source: Selenium – Health Professional Fact Sheet. National Institutes of Health, Office of Dietary Supplements. Updated April 15, 2024. Accessed March 4, 2026. Public domain.

Food	Serving	Selenium (µg)	Percent Daily Value
Brazil nuts	1 oz.	544	989
Shrimp, cooked	3 oz.	42	76
Pork chop	3 oz.	37	67
Beef liver	3 oz.	28	51
Cod	3 oz.	24	44
Cottage cheese, 1% milkfat	1 c.	20	36
Egg, hard boiled	1 large	15	27
Portabella mushroom, grilled	½ c.	13	24
Brown rice	1 c.	12	22
Milk, 1% milkfat	1 c.	6	11
Lentils, boiled	1 c.	6	11
Spinach, boiled	½ c.	5	9
Carrots, raw	½ c.	0	0

References

1. Dennert G, Zwahlen M, et al. Selenium for Preventing Cancer. Cochrane Database of Systematic Reviews. 2018; 1. https://doi.org/10.1002/14651858.CD005195.pub4. Accessed August 29, 2025.

Sulfur

Sulfur is incorporated into protein structures in the body. Amino acids, methionine and cysteine contain sulfur. Indeed, the sulfur in our diet primarily comes from these amino acids as part of our dietary protein. These amino acids are also a necessary part of our antioxidant enzyme glutathione peroxidase. Some vitamins like thiamin and biotin also contain sulfur which are important in regulating acidity in the body. Sulfur is a major mineral with no recommended intake or deficiencies when protein needs are met. Additionally, sulfur is an important component of some B vitamins, which is a source for the some of the sulfur in our diet.

Attributions

Adapted by Pattie S. Green, Ph.D. and Jonathan E. Pottle, Ph.D. at Tacoma Community College from the following sources:

• Human Nutrition by University of Hawai‘i at Mānoa Food Science and Human which is licensed under a CC BY-NC-SA 4.0,
  • Overview of Fluid and Electrolyte Balance
  • Regulation of Water Balance
  • Sodium
  • Potassium
  • Chloride
  • Consequences of Deficiency or Excess
  • Chapter 10. Major Minerals Introduction
  • Calcium
  • Phosphorus
  • Magnesium
  • Fluoride
  • Iron
  • Copper
  • Zinc
  • Iodine
  • Selenium
  • Sulfur
• APUS: An Introduction to Nutriton 1st Edition, “Regulation of Water Balance,” LibreTexts. CC BY-NC-SA 3.0 and
• Anatomy & Physiology, “17.4 The Thyroid Gland,” OpenStax Connexions, shared under CC BY 3.0. Access for free at https://openstax.org/books/anatomy-and-physiology/pages/1-introduction