By Karen Collins, RD, CDN

Once upon a time, vitamin supplements were an “insurance policy” that could lower our risk of diseases if our diets weren’t quite good enough.

However, a wide range of studies now suggests that’s not necessarily true.

Any good or bad effects of supplements are likely to depend on individual differences in age, diet, environments and genetics.

Research suggests that cancer, heart disease and many other chronic diseases involve several common mechanisms affected by nutrients from our foods and beverages. For example, antioxidants protect against free radical damage, while calcium and vitamin D regulate bone metabolism and cell growth.

However, most studies evaluating supplements have shown little or no health benefit, and occasionally even harm.

The effects of age, time

Age and time may explain some of the lack of benefits. Cancer, especially, usually develops over 10 to 20 years or more. Vitamins and minerals that influence DNA repair seem particularly involved in preventing cancer development in its earliest stages.

Most supplement-related studies so far have followed older age groups for two to 10 years. It is possible that supplements provide benefits that don’t show up for the time studied, but more than just time is involved.

A supplement may hold quite different effects for people eating a balanced diet than for those whose diets are lacking. The Linxian Trial, often cited as an example of how beta-carotene, vitamin E and selenium can reduce cancer death rates, was conducted in a Chinese population known to be nutritionally deficient. That’s no basis on which to expect benefits for everyone, regardless of diet.

Affecting mortality 

A 2007 analysis of 68 studies on antioxidant supplements concluded that supplements of vitamin A, beta-carotene and vitamin E could even increase overall mortality rates. Several studies now question the value and safety of large doses of antioxidant supplements, suggesting they could interfere with our bodies’ immune and cancer-fighting functions.

Although more studies are needed, research has shown that supplements can provide benefits for people whose diets do not supply enough of the nutrients required for good health. For example, vegans – vegetarians who eat no animal products – show benefits from vitamin B12 supplements of vitamin B12, while people who don’t consume dairy products might benefit from calcium and vitamin D supplements.

The many people who have trouble meeting recommended amounts of vegetables and fruits may be an exception. Although we might expect supplements of nutrients like beta-carotene and vitamin C to fill the gap, science now suggests that much of the benefit of these foods comes from the natural phytochemicals they contain.

In your genes

Exposures to hazards, such as tobacco smoke, pollution and alcohol, as well as medications, may make some people need more of certain nutrients or may make high doses of antioxidants increasingly hazardous.  Beta-carotene supplements, for example, seemingly increase the risk of lung cancer in smokers.

Genetic differences may also mean that supplements offer protection for some people but not for others. For example, differences in hormone-related genes could explain why vitamin E might protect against prostate cancer in some men but not others.

More studies are underway, but for now the bottom line is that working toward a balanced, plant-based diet is much more certain to reduce cancer and heart disease risk than a blanket one-size-fits-all supplement.

Any supplements should be chosen to fill specific gaps in meeting individual needs, remembering that more is not always better.

•  U.S. Office of Dietary Supplements

•  Council for Responsible Nutrition

•  Weight-Loss Prescription: Calcium, Vitamin D

•  Five Top Q&As About Multivitamins

•  Vim, Vigor, and Vitamins

Karen Collins is a nationally known dietitian and nutrition expert whose work appears on Nubella News, MSNBC.com and other major Web sites. She is nutrition advisor with the American Institute for Cancer Research.

Source: American Institute for Cancer Research
Reference: Nutrition Notes

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