Supplements vs. exercise: Comparing cancer prevention strategies

The ‘‘vitamins’’ in your legs

Dietary supplements are wildly popular in America. According to the third National Health and Nutrition Examination Survey, 40% of all American adults take one or more.

It’s easy to see why supplements are so popular. Because few are regulated by the FDA, manufacturers and retailers can assert many benefits and advertise them aggressively. It’s a good strategy, bringing more than $20 billion a year to the supplement industry. But is it good for your health? Are there other ways to gain the benefits claimed for supplements?

Diet is certainly one alternative; it is clear that a good diet can reduce the risk of many serious diseases. Most scientists agree that extra vitamins in pills or powders add little, if anything, to a well-balanced diet that adheres to current guidelines. Another alternative is at hand (or, perhaps, at foot). In fact, regular exercise is a proven way to achieve many of the benefits claimed for vitamins and other supplements, even for people who also eat properly.

Here’s how exercise and supplements stack up with regard to cancer.

Are supplements safe?

Cancer is the second-leading cause of death in the United States, taking some 560,000 lives in 2007 alone. It’s no wonder that possible protection against cancer is one of the leading reasons that people take supplements in general and antioxidants in particular.

The idea has great appeal. For one thing, many studies confirm that people who eat lots of vitamin-rich fruits, vegetables, and whole grains enjoy a lower risk of cancer than folks who shun these foods. In theory, antioxidants should help counter the harmful effects of free radicals, unstable, high-energy, electrically charged molecules that can damage DNA and cell membranes. Cell damage of this sort could increase the risk of cancer and other diseases. Antioxidants such as vitamin E, vitamin C, and members of the vitamin A–beta carotene family can neutralize free radicals, at least in laboratory experiments.

In the 1980s and early ’90s, antioxidants became the great hope against both cancer and heart disease. Sadly, they have been a flop against both (see table below). Two major randomized clinical trials found that beta carotene actually increases the risk of lung cancer in smokers, just the people who need protection most. A third study reported that vitamin E increases the risk of second cancers in survivors of head and neck cancer. And a 2007 meta-analysis of 68 randomized clinical trials involving 232,606 subjects concluded that beta carotene, vitamin A, and vitamin E, singly or in combination, may actually increase the overall death rate in adults.

The role of supplements in prostate cancer is still being studied. Beta carotene may offer some protection against prostate cancer, but only in nonsmoking men who have very low blood levels due to dietary deficiencies. According to the ATBC Trial (see table), vitamin E may reduce the risk of prostate cancer in smokers, but other randomized clinical trials in nonsmokers found no benefit. Selenium, a mineral with antioxidant properties, may reduce a man’s risk of prostate cancer; the results of individual trials are mixed, but a Canadian meta-analysis reported a 26% overall reduction in risk. More study is needed, and the 32,400-person SELECT Trial of selenium and vitamin E should help answer these questions. And although many men take supplements of soy or lycopene to reduce their risk of prostate cancer, there is no good evidence that they work. Another ingredient of many popular “prostate supplements” is zinc, which may actually do more harm than good. Very large doses of multivitamins or folic acid may also backfire.

Folic acid, a B vitamin, may help reduce the risk of colon cancer, at least in women. Harvard’s Nurses’ Health Study linked the prolonged use of multivitamins containing folic acid with a 75% lower risk of colon cancer. More research is needed to confirm the findings, but it may be a moot point, since folic acid added to cereals and other grains has made it easier than ever to get enough of it from diet, even in people who don’t always get their daily veggies. And a 2007 study found that very high doses of folic acid — 1,000 micrograms a day, which is two-and-a-half times the Recommended Dietary Allowance — increases the risk of colon polyps in people with previous polyps; men may also face an increased risk of prostate cancer.

The authoritative U.S. Preventive Services Task Force has concluded that vitamin supplements do not reduce the risk of cancer. Low-dose aspirin may help, but although you can buy it everywhere without a prescription, it’s a medication, not a supplement, and more research is needed to learn if it really helps.

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Evaluating exercise