Trace Minerals

Trace minerals are present (and required) in very small amounts in the body. An understanding of the important roles and requirements of trace minerals in the human body is fairly recent, and research is still ongoing. The most important trace minerals are iron, zinc, copper, chromium, fluoride, iodine, selenium, manganese, and molybdenum. Some others, such as arsenic, boron, cobalt, nickel, silicon, and vanadium, are recognized as essential for diabetes: inability to regulate level of sugar in the blood osteoporosis: weakening of the bone structure kidney stones: deposits of solid material in kidney malnutrition: chronic lack of sufficient nutrients to maintain health anorexia nervosa: refusal to maintain body weight at or above what is considered normal for height and age bulimia: uncontrolled episodes of eating (bingeing) usually followed by self-induced vomiting (purging)

chronic: over a long period diuretic: substance that depletes the body of water acute: rapid-onset and short-lived plasma: the fluid portion of the blood, distinct from the cellular portion enema: substance delivered via the rectum biological: related to living organisms oxygen: O2, atmospheric gas required by all animals hemoglobin: the iron-containing molecule in red blood cells that carries oxygen myoglobin: oxygen storage protein in muscle neurotransmitter: molecule released by one nerve cell to stimulate or inhibit another genetic: inherited or related to the genes insulin: hormone released by the pancreas to regulate level of sugar in the blood oxidative: related to chemical reaction with oxygen or oxygen-containing compounds infectious diseases: diseases caused by viruses, bacteria, fungi, or protozoa, which replicate inside the body cancer: uncontrolled cell growth caries: cavities in the teeth intravenous: into the veins some animals, while others, such as barium, bromine, cadmium, gold, silver, and aluminum, are found in the body, though little is known about their role in health.

Functions. Trace minerals have specific biological functions. They are essential in the absorption and utilization of many nutrients and aid enzymes and hormones in activities that are vital to life. Iron plays a major role in oxygen transport and storage and is a component of hemoglobin in red blood cells and myoglobin in muscle cells. Cellular energy production requires many trace minerals, including iron, copper, and zinc, which act as enzyme cofactors in the synthesis of many proteins, hormones, neuro-transmitters, and genetic material.

Iron and zinc support immune function, while chromium and zinc aid insulin action. Zinc is also essential for many other bodily functions, such as growth, development of sexual organs, and reproduction. Zinc, copper and selenium prevent oxidative damage to cells. Fluoride stabilizes bone mineral and hardens tooth enamel, thus increasing resistance to tooth decay. Iodine is essential for normal thyroid function, which is critical for many aspects of growth and development, particularly brain development. Thus, trace minerals contribute to physical growth and mental development.

Role in disease prevention and treatment. In addition to clinical deficiency diseases such as anemia and goiter, research indicates that trace minerals play a role in the development, prevention, and treatment of chronic diseases. A marginal status of several trace minerals has been found to be associated with infectious diseases, disorders of the stomach, intestine, bone, heart, and liver, and cancer, although further research is necessary in many cases to understand the effect of supplementation. Iron, zinc, copper, and selenium have been associated with immune response conditions. Copper, chromium and selenium have been linked to the prevention of cardiovascular disease. Excess iron in the body, on the other hand, can increase the risk of cardiovascular disease, liver and colorectal cancer, and neurodegenerative diseases such as Alzheimer's disease. Chromium supplementation has been found to be beneficial in many studies of impaired glucose tolerance, a metabolic state between normal glucose regulation and diabetes. Fluoride has been known to prevent dental caries and osteoporosis, while potassium iodide supplements taken immediately before or after exposure to radiation can decrease the risk of radiation-induced thyroid cancer.

Deficiency. With the exception of iron, dietary deficiencies are rare in the United States and other developed nations. However, malnutrition in developing countries increases the risk for trace-mineral deficiencies among children and other vulnerable groups. In overzealous supplement users, interactions among nutrients can inhibit absorption of some minerals leading to deficiencies. Patients on intravenous feedings without mineral supplements are at risk of developing deficiencies as well.

Although severe deficiencies of better-understood trace minerals are easy to recognize, diagnosis is difficult for less-understood minerals and for mild deficiencies. Even mild deficiencies of trace minerals however, can result in poor growth and development in children.

Iron deficiency is the most common nutrient deficiency worldwide, including in the United States. Iron-deficiency anemia affects hundreds of mil-

lions of people, with highest prevalence in developing countries. Infants, young children, adolescents, and pregnant and lactating women are especially vulnerable due to their high demand for iron. Menstruating women are also vulnerable due to blood loss. Vegetarians are another vulnerable group, as iron from plant foods is less bioavailable than that from animal sources.

Zinc deficiency, marked by severe growth retardation and arrested sexual development, was first reported in children and adolescent boys in Egypt, Iran, and Turkey. Diets in Middle Eastern countries are typically high in fiber and phytates, which inhibit zinc absorption. Mild zinc deficiency has been found in vulnerable groups in the United States. Copper deficiency is rare, but can be caused by excess zinc from supplementation.

Deficiencies of fluoride, iodine, and selenium mainly occur due to a low mineral content in either the water or soil in some areas of the world. Fluoride deficiency is marked by a high prevalence of dental caries and is common in geographic regions with low water-fluoride concentration, which has led to the fluoridation of water in the United States and many other parts of the world. Goiter and cretinism (a condition in which body growth and mental development are stunted) have been eliminated by iodization of salt in the United States, but still occur in parts of the world where salt manufacture and distribution are not regulated. Selenium deficiency due to low levels of the mineral in soil is found in northeast China, and it has been associated with Keshan disease, a heart disorder prevalent among people of that area.

Toxicity. Trace minerals can be toxic at higher intakes, especially for those minerals whose absorption is not regulated in the body (e.g., selenium and iodine). Thus, it is important not to habitually exceed the recommended intake levels. Although toxicity from dietary sources is unlikely, certain genetic disorders can make people vulnerable to overloads from food or supplements. One such disorder, hereditary hemochromatosis, is characterized by iron deposition in the liver and other tissues due to increased intestinal iron absorption over many years.

Chronic exposure to trace minerals through cooking or storage containers can result in overloads of iron, zinc, and copper. Fluorosis, a discoloration of the teeth, has been reported in regions where the natural content of fluoride in drinking water is high. Inhalation of manganese dust over long periods of time has been found to cause brain damage among miners and steelworkers in many parts of the world.

In summary, minerals, both major and trace, play vital roles in human health, and care must be taken to obtain adequate intakes from a wide variety of whole foods. The most common result of deficiencies is poor growth and development in children. Minerals interact with each other and with other nutrients, and caution is required when using supplements, as excess intake of one mineral can lead to the deficiency of another nutrient. see also Anemia; Bioavailability; Calcium; Dietary Supplements; Osteoporosis; Vitamins, Fat-Soluble; Vitamins, Water-Soluble.

Sunitha Jasti

Bibliography

Wardlaw, Gordon M. (1999). Perspectives in Nutrition, 4th edition. Boston: WCB McGraw-Hill.

prevalence: describing the number of cases in a population at any one time fiber: indigestible plant material which aids digestion by providing bulk cretinism: arrested mental and physical development

Whitney, Eleanor N., and Rolfes, Sharon R. (1996). Understanding Nutrition, 7th edition. New York: West Publishing.

Internet Resources

The American Dietetic Association (2002). "Position of The American Dietetic Association: Food Fortification and Dietary Supplements." Available from <http://www .eatright.com>

The Linus Pauling Institute. "Minerals." Available from <http://osu.orst.edu/dept/lpi>

United States Department of Agriculture (2002). "Dietary Reference Intakes (DRI) and Recommended Dietary Allowances (RDA)." Available from <http://www.nal. usda.gov/fnic/>

neurotransmitter: molecule released by one nerve cell to stimulate or inhibit another hormone: molecules produced by one set of cells that influence the function of another set of cells drugs: substances whose administration causes a significant change in the body's function serotonin: chemical used by nerve cells to communicate with one another anxiety: nervousness menopause: phase in a woman's life during which ovulation and menstruation end diet: the total daily food intake, or the types of foods eaten carbohydrate: food molecule made of carbon, hydrogen, and oxygen, including sugars and starches

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