vitamins deficiency symptoms

Effects of zinc on health

Scientists are studying zinc to learn about its effect on the immune system and several health problems.

Immune system and wound healing

Zinc supplements might help some people with sores and skin ulcers, but only if these people have low levels of zinc.

Diarrhea

Children who live in developing countries often die from diarrhea. Zinc supplements might help these children get better more quickly. It is not clear if zinc supplements help children with diarrhea that gets enough zinc, such as most children in the United States.

The common cold

Some scientists have tried to find out whether zinc lozenges help people with a cold feel better and recover more quickly. But these studies have had different results. At this time, it is not clear whether zinc lozenges can help treat the common cold.

Age-related macular degeneration (AMD)

People with AMD lose their vision over time. Zinc might help keep AMD in its early stages from getting worse. In one study, scientists gave older people with AMD a daily supplement with 80 mg zinc, vitamin C, vitamin E, beta-carotene, and copper for about 6 years. The people who took these supplements had a lower chance of getting advanced AMD and lost less of their vision.

The same study showed that taking supplements containing only zinc also lowered the chance of getting advanced AMD in people with a high risk of this disease. People who have or are starting to get AMD might want to talk with their doctor about taking dietary supplements.

Sources of Zinc

A wide variety of foods contain zinc. 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 types of seafood (such as crab and lobster), whole grains, fortified breakfast cereals, and dairy products.

Phytates—which are present in whole-grain breads, cereals, legumes, and other foods—bind zinc and inhibit its absorption. Thus, the bioavailability of zinc from grains and plant foods is lower than that from animal foods, although many grain- and plant-based foods are still good sources of zinc.


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Selenium food sources and supplements

Wheat.

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Selenium occurs in staple foods such as corn, wheat, and soybean as selenomethionine, the organic selenium analogue of the amino acid methionine.

Selenomethionine can be incorporated into body proteins in place of methionine, and serves as a vehicle for selenium storage in organs and tissues. Selenium supplements may also contain sodium selenite and sodium selenate, two inorganic forms of selenium. Selenomethionine is generally considered to be the best absorbed and utilized form of selenium.

Selenium is also available in ‘high selenium yeasts’, which may contain as much as 1,000 to 2,000 micrograms of selenium per gram. Most of the selenium in these yeasts is in the form of selenomethionine. This form of selenium was used in the large scale cancer prevention trial in 1983, which demonstrated that taking a daily supplement containing 200 micrograms of selenium per day could lower the risk of developing prostate, lung, and colorectal cancer.

However, some yeast may contain inorganic forms of selenium, which are not utilized as well as selenomethionine.

A study conducted in 1995 suggested that the organic forms of selenium increased blood selenium concentration to a greater extent than inorganic forms. However, it did not significantly improve the activity of the selenium-dependent enzyme, glutathione peroxidase.

Researchers are continuing to examine the effects of different chemical forms of selenium, but the organic form currently appears to be the best choice.

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Selenium and cancer

Many studies indicate that death from cancer, including lung, colorectal, and prostate cancers, is lower among people with higher blood levels or intake of selenium. In addition, the incidence of nonmelanoma skin cancer is significantly higher in areas of the United States with low soil selenium content.

The effect of selenium supplementation on the recurrence of different types of skin cancers was studied in seven dermatology clinics in the U.S. from 1983 through the early 1990s. Taking a daily supplement containing 200 μg of selenium did not affect recurrence of skin cancer, but significantly reduced the occurrence and death from total cancers. The incidence of prostate cancer, colorectal cancer, and lung cancer was notably lower in the group given selenium supplements.

Research suggests that selenium affects cancer risk in two ways. As an anti-oxidant, selenium can help protect the body from damaging effects of free radicals. Selenium may also prevent or slow tumor growth. Certain breakdown products of selenium are believed to prevent tumor growth by enhancing immune cell activity and suppressing development of blood vessels to the tumor.

However, not all studies have shown a relationship between selenium status and cancer. In 1982, over 60,000 participants of the Nurse’s Health Study with no history of cancer submitted toenail clippings for selenium analysis. Toenails are thought to reflect selenium status over the previous year. After three and a half years of data collection, researchers compared toenail selenium levels of nurses with and without cancer. Those nurses with higher levels of selenium in their toenails did not have a reduced risk of cancer.

Two long-term studies, the SU.VI.MAX study in France and the Selenium and Vitamin E Cancer Prevention Trial (SELECT) in the United States and Canada, investigated whether selenium combined with at least one other dietary supplement could reduce the risk of prostate cancer in men.

The SU.VI.MAX study examined the effects of a supplement package containing moderate doses of vitamins E and C, beta-carotene, zinc, and selenium versus placebo on the risk of chronic diseases such as cancer and cardiovascular disease. Among the 5,141 men enrolled, those randomized to the supplements that began the study with a normal PSA (prostate specific antigen) level at baseline had their risk of prostate cancer reduced by half. Among the men whose PSA levels were elevated at baseline, however, use of the supplements was associated with an increased incidence of prostate cancer of borderline statistical significance compared to placebo.

The Selenium and Vitamin E Cancer Prevention Trial (SELECT) was a very large randomized clinical trial begun in 2001 specifically designed to determine whether 7-12 years of daily supplementation with selenium, with or without synthetic vitamin E (400 IU), reduces the number of new prostate cancers in healthy men (PSA ≤4 ng/ml at baseline).

The trial, which had enrolled >35,000 men, was discontinued in October 2008 when an analysis found that the supplements, taken alone or together for an average of 5.5 years, did not prevent prostate cancer. Study staff members will continue to monitor participants’ health for an additional 3 years.


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