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Volume 2 Published - 14:00 UTC    08:00 EST    19-January-2001      
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Back To Vidyya Facts About Dietary Supplements:


Zinc

Zinc: What is it?

What foods provide zinc?

What is the Recommended Dietary Allowance for zinc for adults?

When can zinc deficiency occur?

Signs of zinc deficiency

Who may need extra zinc?

 

What are some current issues and controversies about zinc?

Zinc, infections, and wound healing

Zinc and the common cold

Zinc and iron absorption

What is the health risk of too much zinc?

Table of food sources of zinc  

Zinc: What is it?
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.

What foods provide zinc?

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 U.S. 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. The table of food sources of zinc suggests many dietary sources of zinc.

What is the Recommended Dietary Allowance for zinc?

"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 each life-stage and gender group." The 1989 RDAs for zinc for adults, in milligrams (mg), are:

Life-Stage  Men  Women  Pregnancy  Lactation
Ages 19 + 15 mg 12 mg    
All ages     15 mg  

 19 mg (first six months)

16 mg (second six months)

Results of two national surveys, the National Health and Nutrition Examination Survey (NHANES III 1988-91) and the Continuing Survey of Food Intakes of Individuals (1994 CSFII) indicated that the diets of many adults, especially older Americans and women, do not provide the recommended amounts of zinc.

When can zinc deficiency occur?

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. Instead, many general signs of zinc deficiency can appear, including 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 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 otherwise a vegetarian diet may be inadequate in zinc. Since the zinc from plant sources is absorbed less readily, this increases the 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. Therefore, to decrease their risk for developing a zinc deficiency, it is important for individuals in these groups to include sources of zinc in their daily diet (see table of food sources of zinc. 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. Breastfeeding increases the risk of depleting nutritional zinc status when dietary zinc intake is chronically low because of the greater need for zinc during lactation.

Zinc deficiency is frequently associated with alcoholism, which is often due to a lower intake of food. The need for a supplement as part of an overall treatment plan is usually evaluated by a physician in this situation.

Diarrhea causes a loss of zinc. Therefore, digestive diseases or gastrointestinal surgery that result in diarrhea are often associated with zinc deficiency. Individuals who experience chronic diarrhea should make sure they include sources of zinc in their daily diet (see table of food sources of zinc). A medical doctor can evaluate the need for a zinc supplement if diet alone fails to maintain normal zinc levels in the body.

What are some 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 indicated 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 considered a serious public health problem in the world today. 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.

What is the health risk of 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.

Table of Food Sources of Zinc (7)

Food  Milligrams %DV*
Oysters, 6 medium  76.4  510
Beef shank, lean only, cooked 3 oz 8.9 60
Beef chuck, lean only, cooked, 3 oz 7.4 45
Beef tenderloin, lean only, cooked, 3 oz 4.8 30
Pork shoulder, lean only, cooked, 3 oz 4.7 25
Pork tenderloin, lean only, cooked, 3 oz 2.2 15
Chicken leg, cooked, 3 oz 2.4 15
Baked beans, canned, 1/2 c 1.8 10
Cashews, dry roasted w/out salt, 1 oz 1.6 10
Pecans, dry roasted w/out salt, 1 oz 1.6 10
Raisin bran, 1 oz 1.5 10
Almonds, dry roasted, unblanched, w/out salt, 1 oz 1.4 9
Chickpeas, mature seeds, canned, 1/2 c 1.3 9
Mixed nuts, dry roasted w/peanuts, w/out salt, 1 oz 1.1 5
Chicken breast, cooked, 3 oz 1.1 5
Bran muffin, 1 medium 1.1 5
Walnuts, black, dried, 1 oz 1.0 5
Milk, 1 c 1.0 5
Yogurt, 1 c 1.0 5
Kidney beans, 1/2 c cooked 0.9 5
Cheese, cheddar, 1 oz 0.9 5
Peas, green, boiled, 1/2 c 0.8 5
Oatmeal, instant, 1 packet 0.8 5
Flounder/sole, cooked, 3 oz 0.5 5

DV = Daily Value. DVs are reference numbers based on the Recommended Dietary Allowance (RDA). They were developed to help consumers determine if a food contains very much of a specific nutrient. The DV for magnesium is 15 milligrams (mg). The percent DV (%DV) listed on the nutrition facts panel of food labels tells adults what percentage of the DV is provided by one serving. Even foods that provide lower percentages of the DV will contribute to a healthful diet.


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Editor: Susan K. Boyer, RN
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