Zinc: What is it?

Zinc is an essential mineral that is found in almost every cell. It stimulates the activity of approximately 100 enzymes, which are substances that promote biochemical reactions in your body . Zinc supports a healthy immune system , is needed for wound healing , helps maintain your sense of taste and smell , and is needed for DNA synthesis . Zinc also supports normal growth and development during pregnancy, childhood, and adolescence .

What foods provide zinc?

Zinc is found in a wide variety of foods . Oysters contain more zinc per serving than any other food, but red meat and poultry provide the majority of zinc in the American diet. Other good food sources include beans, nuts, certain seafood, whole grains, fortified breakfast cereals, and dairy products . Zinc absorption is greater from a diet high in animal protein than a diet rich in plant proteins. Phytates, which are found in whole grain breads, cereals, legumes and other products, can decrease zinc absorption.

What is the Recommended Dietary Allowance for zinc?

The latest recommendations for zinc intake are given in the new Dietary Reference Intakes developed by the Institute of Medicine. Dietary Reference Intakes (DRIs) is the umbrella term for a group of reference values used for planning and assessing nutrient intake for healthy people. The Recommended Dietary Allowance (RDA), one of the DRIs, is the average daily dietary intake level that is sufficient to meet the nutrient requirements of nearly all (97-98%) healthy individuals. For infants 0 to 6 months, the DRI is in the form of an Adequate Intake (AI), which is the mean intake of zinc in healthy, breastfed infants. The AI for zinc for infants from 0 through 6 months is 2.0 milligrams (mg) per day. The 2001 RDAs for zinc for infants 7 through 12 months, children and adults in mg per day are:

Table 1: Recommended Dietary Allowances for Zinc for
Infants over 7 months, Children, and Adults

When can zinc deficiency occur?

Zinc deficiency most often occurs when zinc intake is inadequate or poorly absorbed, when there are increased losses of zinc from the body, or when the body's requirement for zinc increases. Signs of zinc deficiency include growth retardation, hair loss, diarrhea, delayed sexual maturation and impotence, eye and skin lesions, and loss of appetite. There is also evidence that weight loss, delayed healing of wounds, taste abnormalities, and mental lethargy can occur . Since many of these symptoms are general and are associated with other medical conditions, do not assume they are due to a zinc deficiency. It is important to consult with a medical doctor about medical symptoms so that appropriate care can be given.

Who may need extra zinc?

There is no single laboratory test that adequately measures zinc nutritional status. Medical doctors who suspect a zinc deficiency will consider risk factors such as inadequate caloric intake, alcoholism, digestive diseases, and symptoms such as impaired growth in infants and children when determining a need for zinc supplementation. Vegetarians may need as much as 50% more zinc than non-vegetarians because of the lower absorption of zinc from plant foods, so it is very important for vegetarians to include good sources of zinc in their diet .

Maternal zinc deficiency can slow fetal growth . Zinc supplementation has improved growth rate in some children who demonstrate mild to moderate growth failure and who also have a zinc deficiency. Human milk does not provide recommended amounts of zinc for older infants between the ages of 7 months and 12 months, so breast-fed infants of this age should also consume age-appropriate foods containing zinc or be given formula containing zinc . Alternately, pediatricians may recommend supplemental zinc in this situation. Breastfeeding also may deplete maternal zinc stores because of the greater need for zinc during lactation . It is important for mothers who breast-feed to include good sources of zinc in their daily diet and for pregnant women to follow their doctor's advice about taking vitamin and mineral supplements.

Low zinc status has been observed in 30% to 50% of alcoholics. Alcohol decreases the absorption of zinc and increases loss of zinc in urine. In addition, many alcoholics do not eat an acceptable variety or amount of food, so their dietary intake of zinc may be inadequate .

Diarrhea results in a loss of zinc. Individuals who have had gastrointestinal surgery or who have digestive disorders that result in malabsorption, including sprue, Crohn's disease and short bowel syndrome, are at greater risk of a zinc deficiency . Individuals who experience chronic diarrhea should make sure they include sources of zinc in their daily diet and may benefit from zinc supplementation. A medical doctor can evaluate the need for a zinc supplement if diet alone fails to maintain normal zinc levels in these circumstances.