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Though supplements may help certain individuals, people can generally get the nutrients they need from a balanced diet.
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updated 12/11/2003 6:18:43 PM ET 2003-12-11T23:18:43

Despite many studies, the effect of vitamin supplements on heart disease and cancer is uncertain. Clearly, a daily multivitamin is advisable for some people, but for the rest of us, there is too little support to either recommend its use or discourage it. The benefits of a diet high in vegetables, fruits, whole grains and beans, however, remain clear.

People commonly take antioxidants like vitamins C and E. But major medical journals have reported no impact of antioxidant supplements on preventing heart disease. With the possible exception of vitamin E protecting against prostate cancer, there is also little support for cancer prevention.

Studies that show no impact have caused some researchers to question whether they covered a long enough period of time. Heart-related benefits should be seen after a few years, although more time might be necessary. And since most common cancers develop over many years, a few years’ use of supplements may be too brief a time span to see the effects.

Another problem noted at a recent American Institute for Cancer Research (AICR) conference on diet and cancer concerns the form supplements come in. For example, while vitamin E supplements usually consist of alpha-tocopherol, foods contain mainly gamma-tocopherol. So antioxidants could have different effects depending on their chemical form.

The importance of eating whole foods containing antioxidants is shown by beta-carotene. Research indicates that diets supplying beta-carotene and other carotenoids from fruits and vegetables help prevent cancer and heart disease. But beta-carotene from supplements has shown no such benefit. In fact, beta-carotene supplements seem to increase lung cancer and overall mortality in smokers.

Benefits of supplements
Still, supplements are useful to some individuals. For instance, a multivitamin can supply vitamin D to the elderly and those without adequate sun exposure or dairy consumption. Adequate vitamin D and calcium decrease bone loss and fracture rates in seniors.

And while vitamin B-12 is not needed by most of us, since modest amounts of meats or dairy products supply plenty, vegetarians and people over 50 (whose absorption of B-12 from food may diminish) should include a multivitamin or a food fortified with B-12 daily.

Another reason people might use multivitamins is for the folate they contain. This B vitamin protects against heart disease because it helps prevent high blood levels of a substance called homocysteine. Low blood folate and high homocysteine have been linked with fatal heart disease.

The reaction between homocysteine and folate also produces methionine that helps retain the DNA in our genes in a normal form. Lack of folate allows abnormal cells to form that can develop into cancer. Repeatedly, low folate has been linked with greater risk of several forms of cancer, especially colorectal cancer.

Because folate has been added to U.S. grain products since 1998, folate deficiencies are now rare in this country. Still, supplements may benefit those with low folate intake or regular alcohol use.

Potential risk
But supplements may pose danger as well. Evidence at the AICR conference showed that too much folate, or folate supplementation after cancer cells are formed, seems to promote tumor growth.

If you choose to take a multivitamin, check the content of any fortified foods you use regularly. You may already consume the equivalent of a multivitamin from these foods.

Nutrition Notes is provided by the American Institute for Cancer Research in Washington, D.C.

© 2013 MSNBC Interactive Reprints

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