Minerals

Minerals

Definition

Minerals are inorganic nutrients. That is, they are materials found in foods that are essential for growth and health and do not contain the element carbon. The minerals that are relevant to human nutrition are water, sodium, potassium, chloride, calcium, phosphate, sulfate, magnesium, iron, copper, zinc, manganese, iodine, selenium, and molybdenum. Cobalt is a required mineral for human health, but it is supplied by vitamin B₁₂. There is some evidence that chromium, boron, and other inorganic elements play some part in human nutrition, but their role has not been proven.

Description

Minerals should be provided by a normal, healthy diet. In special cases, additional mineral supplements may be called for. Preterm (low birth weight) infants have special needs for calcium, phosphorus, and sodium, as well as extra needs for vitamin D. Iron supplements may also be recommended.

The amount of each mineral that is needed to support growth during infancy and childhood, to maintain body weight and health, and to facilitate pregnancy and lactation , are listed in a table called the Recommended Dietary Allowances (RDA). This table was compiled by the Food and Nutrition Board, a committee that serves the United States government. The values listed in the RDA indicate the daily amounts that are expected to maintain health throughout most of the general population. The actual levels of each inorganic nutrient required by any given individual is likely to be less than that stated by the RDA. The RDAs are all based on studies that provided the exact, minimal requirement of each mineral needed to maintain health. However, the RDA values are actually greater than the minimal requirement, as determined by studies on small groups of healthy human subjects, in order to accommodate the variability expected among the general population.

Because of differences in individual diets and individual needs, the decision regarding any child's need for supplements should be made by the parents after discussion with the pediatrician and, where appropriate, a nutritionist. Children on a well-balanced diet do not require supplements, while those who are picky eaters or who routinely eat a poor diet may benefit from supplementation.

Girls should get their calcium from foods, particularly dairy products, rather than supplements. Dairy products were associated with higher bone mineral density in the spine, while calcium supplements had no such benefit.

General use

The following discussion describes the role of the major minerals in human nutrition.

Iron is essential for the formation of hemoglobin, the chemical in the blood that carries oxygen to the cells. Low levels of iron cause anemia. In severe cases, the children become flabby, and they fail to grow normally. Milder cases of iron deficiency may not produce any physical symptoms, but children may learn at a slower pace than children with a proper amount of iron in their diet. The combination of rice, beans, and meat consumed with fresh citrus fruit provides an excellent source of absorbable iron. Iron supplements are suggested for children who cannot or will not follow a proper diet through the first two years of life.

Calcium is required for proper development of bones and teeth. It is also needed for proper muscle activity and blood clotting. Lack of calcium can cause rickets, a condition in which the bones are soft and develop in abnormal shapes. Calcium must be accompanied by vitamin D in order to have the proper effects. Foods rich in calcium include almonds, swiss cheese, collards, sardines and salmon with bones, spinach, ice cream, kale, beet greens, cheddar cheese, molasses, oysters, milk, and broccoli.

Zinc deficiency has been associated with reduced growth and mental retardation . The best foods for zinc are lamb, beef, leafy grains, root vegetables such as potatoes and carrots, shellfish, and organ meats such as liver or kidneys. While a high fiber diet is important for health, too much fiber can reduce the absorption of zinc and lead to a zinc deficiency.

Iodine is needed in the diet for proper thyroid function. The best source of iodine is fish, but table salt normally has iodine added to it, and even modest amounts of salt will meet the daily iodine requirements.

Fluoride is needed for strong teeth. In many areas, drinking water contains fluoride that meets all normal needs, but for children who do not drink water or drink filtered or bottled water, fluoride supplements may be useful. Fluoride supplements may be useful for infants and then may be discontinued as the child gets older and starts drinking water.

Magnesium is found in so many parts of the body that it is almost impossible to describe the effects of low magnesium levels. The most common problems are twitching, and, because of the need for magnesium in the parathyroid gland, soft bones even when calcium and vitamin D are adequate. Because magnesium is found in most foods, deficiency is usually associated with absorption problems and requires medical attention.

Copper is required for blood and nerve fiber development. It is found in liver, nuts, and seafood.

Phosporus is needed for energy production, metabolism, and healthy bone development. The best sources are milk, cheese, meats, whole grains, eggs, peas, and beans.

Potassium is needed for muscle contractions and nerve function. Good sources of potassium are orange juice, milk, cheese, whole grains, and vegetables.

Selenium is needed for proper thyroid function. It has also been associated with prevention of some types of cancer in adults. Selenium supplements are not normally required except in children with phenylketonuria receiving a low-protein diet, although it may sometimes be associated with thyroid problems. In these cases, medical care is required.

Precautions

Although the greatest nutritional concern is with inadequate levels of minerals, it is possible to take too much, particularly when people already eating a normally healthy diet take supplements. The daily intake of minerals should be reviewed to prevent adverse effects.

Excess calcium may lead to constipation and kidney problems. Too much zinc may lead to diarrhea , vomiting , and kidney and heart problems. Excess iron may cause problems of the stomach and digestive tract, liver problems, an increased risk of diabetes, and male sexual problems.

Side effects

When minerals are taken properly, they have no side effects.

Interactions

Minerals can interact with drugs and in excess with each other. Iron and calcium are known to bind to drugs of the tetracycline family and inactivate the antibiotic. The compound of calcium and tetracycline may also be absorbed into a child's teeth, causing discoloration.

Too much calcium in the diet may inhibit absorption of iron, magnesium, phosphorus, and zinc. Excess iron may reduce the absorption of zinc.

Parental concerns

Following a proper balanced diet is the best prevention of both mineral deficiency and mineral overdose. Since many children and adolescents cannot or will not eat a balanced diet, the possible need for supplements should be discussed with an appropriate professional.

Many children fail to follow a proper diet. This may be because of excess intake of fast foods and snack foods of low nutritional value. It is important for parents to teach children the benefits of proper nutrition and the importance of maintaining a healthful diet.

At the same time, adolescents, particularly those who engage in sports , may feel that they will do better with increased levels of nutrients. Because of the risk of toxic reactions to minerals and some vitamins , children should be discouraged from taking vitamin supplements unless there is clear evidence of increased need.

KEY TERMS

Inorganic —Pertaining to chemical compounds that are not hydrocarbons or their derivatives.

Parathyroid gland —A pair of glands adjacent to the thyroid gland that primarily regulate blood calcium levels.

Phenylketonuria (PKU) —A rare, inherited, metabolic disorder in which the enzyme necessary to break down and use phenylalanine, an amino acid necessary for normal growth and development, is lacking. As a result, phenylalanine builds up in the body causing mental retardation and other neurological problems.

Rickets —A condition caused by the dietary deficiency of vitamin D, calcium, and usually phosphorus, seen primarily in infancy and childhood, and characterized by abnormal bone formation.

Resources

BOOKS

Siberry, George K., and Robert Iannone, eds. The Harriett Lane Handbook, 15th ed. St. Louis, MO: Mosby, 2000.

PERIODICALS

Chanoine, J. P. "Selenium and thyroid function in infants, children, and adolescents." Biofactors 19 (2003): 137–43.

Matkovic, V., et al. "Nutrition influences skeletal development from childhood to adulthood: a study of hip, spine, and forearm in adolescent females." Journal of Nutrition 134 (March 2004): 701S–5S.

ORGANIZATIONS

American Dietetic Association. 120 South Riverside Plaza, Suite 2000, Chicago, IL 60606–6995. Web site: <www.eatright.org>.

Tom Brody, PhD Samuel Uretsky, PharmD