Minerals are naturally occurring inorganic substances that are obtained from food and perform a range of important functions in the body. Minerals are categorized as major minerals, or macronutrients, which are present in the body in amounts greater than five grams; and trace minerals, which are present in amounts below five grams. Trace minerals are sometimes called micronutrients.
Major minerals
The major minerals consist of calcium, phosphorus, potassium, sulfur, sodium, chloride, and magnesium. Sodium, potassium, and chloride are sometimes grouped together as electrolytes. An electrolyte is a substance that breaks down into ions when it is dissolved in a suitable medium and thus becomes a conductor of electricity. Each of the major minerals aids in maintaining the body's fluid, electrolyte, and acid-base balance as well as having specific functions.
CALCIUM. Calcium is the most abundant mineral in the human body; 99% of it is stored in the bones and teeth. Calcium maintains bone structure and helps regulate blood calcium levels. This mineral is also necessary for the transport of electrical ions across cell membranes. Inadequate calcium intake during childhood and adulthood can result in osteoporosis, in which there is loss of bone substance. Many Americans do not get enough calcium in their diets. Good dietary sources of calcium include milk, broccoli, mustard greens, kale, cheese, and sardines. The recommended dietary allowance (RDA) of calcium for adults is about 800 mg.
PHOSPHORUS. Phosphorus is also an abundant mineral. Most of the phosphorus—about 80%—that occurs in the body is combined with calcium in the bones and teeth. Phosphorus plays a role in the energy metabolism of cells; helps maintain the body's acid-base balance; and is needed for tissue growth and renewal. Animal products that are high in protein, such as milk, cottage cheese, and steak, are excellent sources of phosphorus. Deficiencies of phosphorus are rare except in patients taking antacids for long periods of time. The RDA of phosphorus for adults is 800 mg.
MAGNESIUM. About 50% of the body's magnesium is in the bones, with the remainder in the cells of the muscles and soft tissues. Magnesium functions in the operation of enzymes and aids in the metabolism of calcium, potassium, and vitamin D. Magnesium deficiency can result from a low intake of the mineral, from diarrhea, and from alcoholism. Magnesium deficiency can cause hallucinations and has been associated with heart problems. Good dietary sources of magnesium include spinach, oysters, baked potatoes, and sunflower seeds.
Magnesium is used in a number of over-the-counter preparations as an antacid and laxative. The most common uses of magnesium in clinical medicine include treatment of tachycardia (excessively rapid heartbeat), and depletion of electrolytes (chloride, potassium, and sodium). It is also used to manage premature labor. The RDA of magnesium is 350 mg for men, 280 mg for women.
SODIUM. Sodium is a mineral that plays an important role in the proper functioning of nerves and muscles. It is also an important component of intracellular fluid. Sodium deficiency does not occur with a normal diet, but may result from illness or injury. Too much sodium in the diet may raise blood pressure and cause hypertension. Salt is the main source of sodium in the diet, but table salt is not the most significant source of sodium. Most sodium in the average American's diet comes from processed and fast foods. The RDA of sodium is between 100 and 3300 mg.
POTASSIUM. Potassium helps maintain fluid and electrolyte balance in the body. Potassium is found in a variety of foods; however, potassium deficiency can result from illness, injury, or treatment with diuretics. The best sources of dietary potassium are fresh fruits and vegetables, especially bananas, potatoes, and raisins. The RDA of potassium is between 1875 and 5625 mg.
CHLORIDE. Chloride helps maintain fluid balance in the body. It is an essential component of the hydrochloric acid in the gastric fluid required for digestion. Chloride deficiency can result from repeated vomiting, diuretic therapy, or kidney disease. The RDA of chloride is between 1700 and 5100 mg.
SULFUR. Sulfur occurs in the body in such other compounds as thiamine and proteins. It helps to maintain the structure of skin, hair, and nails, and functions in oxidation/reduction reactions. Sulfur deficiency is a relatively unusual condition, because the body's need for sulfur is satisfied by the amino acids contained in foods high in protein.
Trace minerals
The trace minerals, or micronutrients, include iron, iodine, zinc, fluoride, selenium, chromium, and copper. Even though these elements are present in very small amounts in the human body, they serve many important functions.
IRON. Iron is a component of hemoglobin in red blood cells and myoglobin in muscle cells. It helps these compounds to hold and carry oxygen throughout the blood and the muscles. Iron also aids in enzyme activity and cell synthesis. Lack of iron in the diet can cause iron-deficiency anemia, which is the most common nutrient deficiency in the world. Symptoms include tiredness, weakness, and a tendency to feel cold. Animal foods such as meat, poultry, and fish are excellent sources of iron. Vitamin C also helps promote the absorption of iron. The RDA of iron is 10 mg for men, 18 mg for women.
IODINE. Iodine is a mineral that is needed for the hormone thyroxine, which plays a part in energy metabolism. Iodine deficiency causes an enlargement of the thyroid gland in the neck, which is known as a goiter. A deficiency in pregnant women can also result in mental and physical retardation known as cretinism. Iodine can be found in seafood, foods grown on land, and bakery products. The RDA of iodine is 150 micrograms.
ZINC. Zinc is needed in only very small amounts, but it functions in nearly every organ of the body. It plays a role in the immune system, sperm production, taste perception, and wound healing. Inadequate intakes of zinc can result in poor growth and appetite as well as poor taste acuity. Too much zinc can impair the absorption of iron and copper in the body. Sources of zinc include meat, shellfish, poultry, legumes, and whole grains. The RDA of zinc is 15 mg.
SELENIUM. Selenium is a relatively rare nonmetallic trace element; there is less than 1 milligram of selenium in the average human body. The selenium is concentrated in the liver, kidneys, and pancreas; and in males, in the testes and seminal vesicles. It also activates thyroid hormone, which regulates the body's metabolism. Selenium can be found in a variety of foods; good sources of it include brewer's yeast, wheat germ, wheat bran, kelp (seaweed), shellfish, brazil nuts, barley, and oats. Selenium is most widely recognized as a substance that speeds up the metabolism of fatty acids and works together with Vitamin E (tocopherol) as an antioxidant. Antioxidants are organic substances that are able to counteract the damage done by oxidation to human tissue. The RDA of selenium is between 0.05 and 0.2 micrograms.
FLUORIDE. Fluoride has not been proven to be an essential mineral, but it does play a role in forming bones and teeth. Fluoride is most readily available from fluoridated drinking water. Too much of this element can cause a discoloration of the teeth known as fluorosis, but adequate fluoride consumption throughout life will help protect against dental caries. The RDA of fluoride is between 1.5 and 4.0 mg.
CHROMIUM. Chromium is closely associated with the hormone insulin, which regulates blood glucose levels. Chromium is usually depleted during food processing, which increases the chance for a deficiency if fast foods are eaten very often. Good sources of chromium include liver, whole grains, cheese, and nuts. The RDA of chromium is between 0.05 and 0.2 mg.
COPPER. Copper helps to form hemoglobin and collagen in the body as well as enzymes. Copper deficiency can impair growth and development, but is rarely encountered. Copper toxicity is also rare, but can occur from too much supplementation. Copper can be found in cherries, legumes, whole grains, seafood, nuts, and organ meats. The RDA of copper is 2–3 mg.
OTHER MICRONUTRIENTS. There are other trace minerals found in the body including boron, molybdenum, cobalt, and nickel. These minerals are all important to the body's health, but they are readily available in a normal diet. Deficiencies of these micronutrients are extremely rare.
KEY TERMS
Acid-base balance—The balance between the acidity and alkalinity of body fluids.
Antioxidant—A substance that works to counteract the damage done by oxidation to human tissue. Dietary antioxidants include the trace mineral selenium.
Electrolyte—An element or compound that dissociates in water and acts as a conductor of electricity.
Hemoglobin—A protein found in red blood cells that carries oxygen from the lungs to the tissues of the body.
Inorganic—Pertaining to chemical compounds that are not hydrocarbons or their derivatives.
Myoglobin—A form of hemoglobin found in muscle tissue.
Trace element—An element that is required in only minute quantities for the maintenance of good health. Trace elements are also called micronutrients.
Complications
Vitamin and mineral supplementation has become a very common practice in the general population, due in part to aggressive advertising and marketing of dietary supplements. While vitamin and mineral supplements are beneficial to those whose diets are lacking in certain nutrients, extremely high doses of some minerals can have toxic effects. For example, too much iron can cause tissue damage and infection. High levels of magnesium can cause depressed deep tendon reflexes, fatigue, and sleepiness. High levels of selenium have been associated with tooth decay.
On the other hand, care should be taken to meet the body's needs for higher levels of mineral intake during pregnancy and periods of high physical or emotional stress (surgery, trauma, etc.).
Health care team roles
Professional dietitians and other nutrition experts are primarily responsible for recommending mineral supplementation when it is necessary and for educating consumers on the dangers of excess supplementation. They also play a role in educating the public on the benefits of eating a well-balanced diet in order to receive adequate amounts of the various minerals.
Dentists and dental hygienists should instruct patients about the importance of dietary calcium and fluoridated water to healthy teeth.
Physicians, registered nurses, and pharmacists should instruct patients about the possible side effects of certain medications— particularly diuretics, antihypertensives, and some types of laxatives— that may cause electrolyte imbalance. Emergency room personnel should be knowledgeable about mineral deficiencies and mineral toxicities in the differential diagnosis of such symptoms as cardiac arrhythmias, seizures, disorientation, muscle twitching, and muscle weakness.
BOOKS
Baron, Robert B., MD, MS. "Nutrition." Current Medical Diagnosis & Treatment 2001. Edited by Lawrence M. Tierney, Jr., MD, et al. New York: Lange Medical Books/McGraw-Hill, 2001.
Mahan, Kathleen L., and Sylvia Escott-Stump. Krause's Food, Nutrition, and Diet Therapy. 10th ed. Philadelphia: W. B. Saunders Company, 2000.
The Merck Manual of Diagnosis and Therapy. Edited by Mark H. Beers, MD, and Robert Berkow, MD. Whitehouse Station, NJ: Merck Research Laboratories, 1999.
Russell, Percy J., and Anita Williams. The Nutrition and Health Dictionary. New York: Chapman & Hall, 1995.
Sizer, Frances S., and Eleanor N. Whitney. Nutrition: Concepts and Controversies, 7th ed. Belmont, CA: Wadsworth Publishing Company, 1997.
ORGANIZATIONS
Committee on the Scientific Evaluation of Dietary Reference Intakes. Institute of Medicine (1997) Dietary Reference Intakes for Calcium, Phosphorus, Magnesium, Vitamin D, and Fluoride. Washington, DC: National Academy Press, 1997.
Nutrition Hotline, American Dietetic Association. 216 West Jackson Blvd., Suite 800, Chicago, IL 60606. (800) 366-1655.
