Zinc
Zinc has been known for more than 50 years to be an essential mineral. It is found in almost every cell in the body and is contained within more than 200 enzymes, substances needed for biochemical reactions. Zinc is important for a healthy immune system, for healing cuts and wounds, and for maintaining your sense of taste and smell. Zinc also supports normal growth and development during pregnancy, childhood, and adolescence.
Where is it?
Meat and poultry provide the majority of zinc in the American diet. Other food sources include beans, nuts, and dairy products. Oysters are the food containing the most zinc by weight, but beef is a more common source in the US diet. The zinc found in meat and oysters is easily absorbed by the body. Dietary phytates, which are found in whole grain cereals and unleavened bread, may significantly decrease the body's absorption of zinc.
How much do we need?
The Recommended Dietary Allowance (RDA) is the average daily dietary intake level that is sufficient to meet the nutrient requirements of nearly all (97 - 98%) individuals in a given life-stage and gender group. The 1989 RDAs for zinc in milligrams (mg), are: 15 mg for adult men and 12 mg for adult women; 15 mg during pregnancy; 19 mg for the first six months of breast feeding and 16 mg during the second six months of nursing a baby.
Zinc deficiency
Zinc deficiency can occur when zinc intake is inadequate, when there are increased losses of zinc from the body, or when the body's requirement for zinc increases. There is no specific deficiency disease associated with zinc. General signs of zinc deficiency include poor appetite, weight loss, delayed healing of wounds, taste abnormalities, and mental lethargy. As body stores of zinc decline, these symptoms worsen and are accompanied by diarrhea, hair loss, recurrent infection, and a form of dermatitis -- a skin disorder. Zinc deficiency has also been linked to poor growth in childhood.
Who may need extra zinc?
There is no single laboratory test available to determine zinc nutritional status. Instead, dietary intake is typically used to estimate the risk of a zinc deficiency. People who may benefit from a zinc supplement include those who do not consume enough calories, vegetarians, the elderly, pregnant and lactating women, and people who suffer from alcoholism or digestive diseases that cause chronic diarrhea.
Anyone with a low caloric intake is at higher risk for having a low zinc intake and for developing a zinc deficiency. Vegetarians who consume a variety of legumes and nuts will probably meet their zinc requirement, but the zinc from plant sources is absorbed less readily, so there is some concern about zinc status in vegetarians who do not consume legumes and nuts.
Dietary surveys suggest that many Americans aged 51 and older, pregnant women and breastfeeding mothers do not consume recommended amounts of zinc. It is important for individuals in these groups to include sources of zinc in their daily diet. Zinc supplementation has been found to improve the growth rate in children with mild zinc deficiency and mild to moderate growth failure. Maternal zinc deficiency can delay fetal growth, and mothers who give birth to small for gestational age babies have been found to have lower zinc intakes during pregnancy.
A medical doctor can evaluate the need for a zinc supplement if diet alone fails to maintain normal zinc levels in the body.
Current issues and controversies about zinc
Zinc, infections, and wound healing
The immune system is adversely affected by even moderate degrees of zinc deficiency. People who are zinc-deficient have a more difficult time resisting infections. T-cell lymphocytes, white blood cells that help fight infection, do not function efficiently when zinc stores are low. When zinc supplements are given to individuals with low zinc levels, the numbers of T-cell lymphocytes circulating in the blood increase and the ability of lymphocytes to fight infection improves. Studies show that poor, malnourished children in India, Africa, South America, and Southeast Asia experience shorter courses of infectious diarrhea after taking zinc supplements. Zinc supplements are often used to treat skin ulcers or bed sores , but they do not increase rates of wound healing when zinc levels are normal.
Zinc and the common cold
A study of over 100 employees of the Cleveland Clinic showed that zinc lozenges decreased the duration of colds by one-half. Some of the participants reported fewer days of congestion and nasal drainage, but no differences were seen in how long their fevers lasted or in the level of muscle aches they experienced. However, this study has been criticized by some researchers who believe that since zinc lozenges often have a bad taste, the participants may have known the difference between the supplement and placebo, which would compromise the results. Also, since other studies have shown no benefit the debate continues on the true value of zinc supplements for cold symptoms.
Zinc and iron absorption
Iron deficiency anemia is a serious public health problem. Iron fortification programs were developed to prevent this deficiency and they have been credited with improving the iron status of millions of women, infants, and children. Some researchers, however, have raised concern about the effects of iron fortification on other nutrients, including zinc. Iron taken in solution can inhibit the absorption of zinc, but foods fortified with iron do not.
Is there a risk of taking is too much zinc?
The health risk of taking too much zinc is moderate to high. Zinc toxicity has been seen in both acute and chronic forms. Intakes of 150 to 450 mg of zinc per day have been associated with low copper status, altered iron function, reduced immune function, and reduced levels of high-density lipoproteins (the good cholesterol). One case report cited severe nausea and vomiting within 30 minutes after the person ingested four grams of zinc gluconate (570 mg elemental zinc). The 1989 RDA committee stated that "chronic ingestion of zinc supplements exceeding 15 mg/day is not recommended without adequate medical supervision." The National Academy of Sciences is currently reviewing recent research and considering new recommendations on zinc intake and risk.
Some food sources of zinc
- Oysters, 6 medium: 76.4 mg of zinc
- Beef chuck, lean, cooked, 3 oz: 7.4 mg
- Pork tenderloin, lean, cooked, 3 oz: 2.2 mg
- Baked beans, canned, 1/2 c: 1.8 mg
- Cashews, unsalted, dry roasted, 1 oz: 1.6 mg
- Pecans, unsalted, dry roasted, 1 oz: 1.6 mg
- Raisin bran, 1 oz: 1.5 mg
- Chickpeas (garbanzo beans) canned, 1/2 c: 1.3 mg
- Milk or yogurt, 1 c: 1.0 mg
- Flounder/sole, cooked, 3 oz: .5 mg
Information provided by the
National Institutes of Health
Article Created: 2000-07-12
Article Updated: 2000-07-12
Each year, Medical College of Wisconsin physicians care for more than 180,000 patients, representing nearly 500,000 patient visits. Medical College physicians practice at Children's Hospital of Wisconsin, Froedtert Memorial Lutheran Hospital, the Milwaukee VA Medical Center, and many other hospitals and clinics in Milwaukee and southeastern Wisconsin.
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