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ZINC

Claims, Benefits: Cures/shortens colds, relieves prostate symptoms, prevents eye disease.

Zinc is an essential mineral for human health. There is no convincing evidence that zinc lozenges fight colds. Zinc is not recommended for prostate problems. Don't take zinc supplements, but do eat foods rich in zinc. There's no reason to exceed the RDA for zinc—15 milligrams daily—which is the amount in most multivitamins.

What’s New About Zinc

Zinc is essential for health. It’s needed for the enzymes that regulate cell division, growth, wound healing, and proper functioning of the immune system. The mineral also plays a role in acuity of taste and smell. No wonder that zinc supplements are sold for so many different purposes. However, there are drawbacks and dangers in zinc supplementation.

Zinc is plentiful in foods. Meats, seafood (especially oysters), and liver are the richest sources; brewer’s yeast, milk and other dairy products, beans, and wheat germ also supply some zinc. Water contains small amounts, too. Severe zinc deficiency is most often found in the developing world, but mild deficiencies may occur elsewhere in undernourished people and those on strict vegetarian diets, which may not contain much zinc. Because they often have a poor diet, older people may also not consume enough zinc. The RDA (recommended dietary allowance) is 11 milligrams a day for men, 8 milligrams for women.

Like many other nutrients, zinc often makes headlines—as a cure for the common cold and eye disease, among other things. Here are some frequently asked questions:

What’s wrong with consuming a lot of zinc?

The zinc in foods can’t hurt you, but supplementary zinc can. Large doses (50 milligrams or more) can interfere with the body’s absorption of copper, another mineral essential to immune function. Large doses can impair blood cell formation and depress the immune system. In addition, they can reduce levels of HDL (“good”) cholesterol.

Can zinc prevent prostate problems—or does it promote cancer?

The prostate gland 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 supplements will cure prostate problems or enhance sexual performance. People have believed for centuries that oysters, a zinc-rich food, promote potency, but there is no evidence that they do.

The findings about zinc and cancer have been contradictory. As we reported in November 2003, a study at the National Cancer Institute did find that men who took more than 100 milligrams of zinc a day were twice as likely to develop advanced prostate cancer, especially if they had taken it for 10 years or more, compared with those who took no zinc. Zinc does increase blood levels of testosterone, which may promote prostate cancer. This is another reason to avoid high doses of zinc.

Can zinc prevent eye disease? Treat macular degeneration?

Zinc may help protect against age-related macular degeneration (AMD), or at least retard it in those who already have the disease. This condition, a major cause of blindness in older adults, is thought to be caused by damage to the retina caused by free radicals. Zinc helps guard retinal tissues, and is found in high concentrations in the retina. Two years ago a study found that a supplement containing zinc, carotenoids, and other nutrients slowed down AMD in those who already had the disease (see Wellness Letter, August 2002). But the recommended daily dose of this supplement contains a hefty 70 milligrams of zinc. If you have AMD or are at high risk for it, it’s worth talking with your doctor about this. Men need to weigh the possible benefits against the potentially increased risk of prostate cancer.

Can zinc prevent or remedy the common cold?

Lozenges, nasal sprays, gels, and even zinc lollipops are sold to treat or prevent colds. In lab studies, high amounts of zinc can block rhinoviruses (the leading cause of colds) from adhering to the nasal lining and/or replicating themselves. But nobody knows what effect zinc has on colds outside the lab—controlled studies have yielded contradictory findings. Recently researchers from the Cleveland Clinic found that a zinc nasal gel can reduce cold symptoms if taken within two days of the onset of a cold. Other studies show no such benefit. There’s no evidence that zinc will prevent colds.

Does taking calcium interfere with zinc absorption and put you at risk for a deficiency?

Minerals can compete with one another in the body, and calcium may interfere somewhat with zinc absorption. But taking calcium supplements will not result in an actual zinc deficiency.

Bottom line: Don’t take zinc supplements, but do eat foods rich in zinc. If you are a vegan, are over 60, or are for any reason not consuming adequate zinc, consider taking a multivitamin/mineral supplement with zinc. There’s no reason to exceed the amount in most multivitamins (15 milligrams). If you have AMD, talk with your doctor about supplements.

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