It may be true. A study published in the Journal of the American Medical Association in 1996 found that people taking 200 micrograms of selenium a day for over four years had a 46% lower risk of lung cancer, 63% lower risk of prostate cancer, and 58% reduction in colorectal cancer. Overall, the cancer risk dropped by 37% compared to people taking a placebo.

If a pharmaceutical company came out with a drug that could reduce the risk of cancer to this degree, then just about every doctor in the country would prescribe it. You would likely find full-page ads in newspapers and magazines: "Ask your doctor for this new drug." Sometimes, when I lecture, I'll ask people how many were prescribed selenium by their physicians, and very few raise their hands.

Any time a new therapy comes along, the most important questions to ask are, "What is the scientific evidence that it is effective? What are the potential side effects? How much does it cost?" Physicians sometimes refer to this as the "risk/benefit ratio." In the case of selenium, the potential benefit is great, the cost is very low, and the side-effects and risk are very low. Although this study needs to be replicated, the potential benefits are so great and the risks and costs are so low, I now recommend selenium for most people. Selenium was first linked with reduced cancer risk in the 1960s. Theories about how the trace element could work to prevent tumors include the following: it may act as an antioxidant; it may be able to alter how the body processes carcinogens; it may have an effect on how proteins are made; or selenium may play a role in how the immune system functions.