Think Zinc
For: Wellness Facts,
November 2003
It's been known for over a century that zinc is essential for health in both plants and animals. Zinc is an important fertilizer ingredient today and thus one factor in the agricultural productivity of our times. In humans zinc is essential for the enzymes that regulate cell division, growth, wound healing, and proper functioning of the immune system. Male children severely deficient in zinc will not develop sexually, though no such cases have ever been reported in this country. The mineral also plays a role in acuity of taste and smell.
Meats, seafood (especially oysters), and liver are the richest sources of zinc; brewer's yeast, milk, beans, and wheat germ also supply some. It occurs in water, too. Severe zinc deficiency is most often found in the developing world, but mild deficiencies may also occur elsewhere in undernourished people and those on strict vegan diets, which may not contain much zinc. Very high fiber intake can interfere with zinc absorption. Older people may not consume much zinc—but zinc absorption is not impaired by aging. The RDA (recommended dietary allowance) is 15 milligrams a day for men, 12 milligrams for women.
However, there are drawbacks and dangers in zinc supplementation. Most people don't need zinc pills. You'll get enough zinc on the semi-vegetarian diet we recommend, which is based on fruits, whole grains, vegetables, and low-fat or fat-free dairy products, plus small amounts of meat and fish.
Like other nutrients, zinc has been making headlines lately. Here are some frequently asked questions.
Does taking calcium pills interfere with zinc absorption and put you at risk for deficiency?
It may interfere with absorption, but there's no evidence this can lead to actual deficiency. If you take calcium supplements to help keep your bones strong but consume little or no zinc, you might need to take a multivitamin/mineral containing zinc. Most multivitamin/mineral pills contain 100% of the RDA for zinc. Minerals can compete with one another in the body, but taking calcium supplements should not result in zinc deficiency.
What's wrong with consuming a lot of zinc?
The zinc in foods can't hurt you, but supplementary zinc can be harmful. Taking large doses can interfere with the body's absorption of copper and iron, other minerals essential to immune function. Megadoses of zinc can impair formation of red blood cells and depress the immune system. In addition, they can reduce levels of HDL ("good") cholesterol. Even doses as small as 50 milligrams a day can have adverse effects, including nausea and gastrointestinal problems.
Can zinc prevent prostate problems and improve erections?
There's no evidence that it can. The prostate gland normally contains high concentrations of zinc, and it's true that a zinc deficiency can cause a drop in testosterone levels. But that doesn't mean that zinc pills will cure prostate problems or boost sexual performance. People have believed for centuries that oysters, a zinc-rich food, promote potency, but there is no evidence for this.
Can zinc prevent eye diseases?
Zinc may protect against age-related macular degeneration (a major cause of blindness in older adults), which is thought to result from damage to the retina by compounds called free radicals.
Zinc helps guard retinal tissues. One study suggested that people with high intakes of zinc from food have a lower risk for age-related macular degeneration. More studies are needed. It makes sense, for many reasons, to eat a zinc-rich diet. But it's too soon to take supplements in hope of preventing macular degeneration.
Can zinc prevent or remedy the common cold?
As we've reported (November 1996), zinc gluconate lozenges have made national news as a potential weapon against colds. The claim is that they reduce the duration of a cold by three days. Millions, perhaps billions, of these lozenges have been sold, though there have been serious questions about the research backing them. But the craze will no doubt die down. Studies conducted more recently have failed to show that zinc lozenges have any more effect than a placebo.
Can zinc cure taste disorders in older people?
Some taste disorders are caused by a zinc deficiency, but this seems to be uncommon—most taste disorders in the elderly are not caused by a zinc deficiency. In some cases, a serious medical condition (such as liver or kidney disease) predisposes a person to both the taste disorder and zinc depletion. If you have a normal diet, it's highly unlikely that you're deficient in zinc, since the mineral is found in so many foods.
Words to the wise: Don't take zinc supplements unless your doctor has prescribed them, but do eat foods rich in zinc. If you are taking high doses of calcium and are a vegan, consider taking a multivitamin/mineral supplement with zinc. (People over 65 may also want to take a multi for this and other reasons.) There's no reason to exceed the RDA for zinc—15 milligrams daily—which is the amount in most multivitamins.
UC Berkeley Wellness Letter, October 1998
