After 15 years of multivitamin use women in the Nurses’ Health Study were found to have one-forth the risk of developing colon cancer (Ann Intern Med 1998;129:517-524). In this research 88,756 women who were free of cancer were studied from 1980 to 1994, and 442 women developed new cases of colon cancer. Higher folate intake in 1980 was related to a lower risk for colon cancer. Folate from dietary sources alone was also related to a modest reduction in risk for colon cancer. The authors concluded, "Long-term use of multivitamins may substantially reduce risk for colon cancer. This effect may be related to the folic acid contained in multivitamins."

JM: Inadequate intake of folic acid may lead to abnormalities in DNA synthesis or repair, which may cause colon cancer. In this study high levels of folic acid (>400 micrograms daily) were required to see benefits. Folic acid has also been reported to reduce the risk of neuro tube defects in the developing fetus, and reduce the risk of heart attacks, strokes and blood clots in adults.

The authors felt vitamin supplementation was even more beneficial than eating a diet high in folic acid. However, I feel this is the wrong message to give people--the idea that they can cleanse the harm done by their bacon and eggs with their morning vitamin supplement. Folic acid comes from plants (foliage). Plant-foods have may qualities that keep people healthy and free of heart disease, strokes, and colon cancer. In fact in parts of the world where people subsist almost entirely on plant food based diets--like rural Africa and Asia--heart disease and colon cancer are essentially unknown--until these people move to the cities and switch to a Western-type diet.

So what’s the harm in playing it safe and adding a vitamin supplement to a healthy diet? Probably none. But we don’t really know for sure. The subjects in the Nurses’ Study all ate the American diet. I would not expect see the same benefits for people on a plant-based diet, because their risk of colon cancer would be very low from their diet. Furthermore, vitamin supplements, in particular beta carotene, have been linked to more cancer. Lung cancer was found to be more common in smokers who took this vitamin (N Engl J Med 334:1145 & 334:1150). The reason may be that there are over 50 compounds known as carotenoids that compete for a "carotenoid receptor site" in the cells. When an overdose of one carotenoid--beta carotene-- is given then the other 49 similar compound cannot attach and perform their functions. Therefore, giving large amounts of vitamins in pills is not the same as giving vitamins in their natural well balanced packages--fruits and vegetables.

Selenium and prostate cancer

Selenium, an essential trace nutrient found largely in grains, fish, and meats, enters the food chain through plants at a rate dependent on selenium concentrations in the soil. For this reason, dietary selenium intake varies substantially across populations. Over 30 years ago it was that cancer

mortality rates in the USA correlated inversely with selenium exposure, as reflected by concentrations in plants. In the subsequent decades, the association between blood concentration of selenium and risk of various cancers has been explored in several epidemiological studies. Until recently, there had been sparse data on selenium intake and risk of prostate cancer. In a study published in 1996 in the Journal of the American Medical conducted in patients with histories of basal and squamous carcinoma who were living in areas of the USA with low soil selenium content found that men taking 200 mg of selenium daily for 4-5 years had about one-third the risk for postate cancer compared with those given placebo. Another study published in a 1998 issue of the Journal of the National Cancer Institute found an inverse association between advanced prostate cancer and toenail selenium concentrations. Those with the highest selenium intake had about one-third the risk of developing prostate cancer compared to those with the lowest. Therefore a supplemental intake of 200 mg of selenium daily may result in a substantial decrease in prostate cancer which may be seen in a short a time as 3 years. The men most likely to benefit would be those who have a low selenium intake in their diet, because the plant foods were grown on selenium poor diets. Eating plant foods grown from a wide variety of geographical regions would be one way to assure adequate intake of this relatively non-toxic essential mineral. However, to assure adequate intake a supplement would be your safest bet.