Some early studies suggested that two supplements—vitamin E and selenium—offered a protective effect against prostate cancer. Based on these findings, the National Cancer Institute (NCI) sponsored a major clinical trial in 2001 in which more than 35,000 men were randomly assigned to take one of the supplements, both together, or a placebo.
In October 2008, the NCI announced it was halting the trial because there was no benefit from either supplement or the two supplements in combination. In fact, data showed slightly more cancer cases among those taking vitamin E and slightly more cases of diabetes among the selenium takers. Although the initial findings could have been due to chance, an updated analysis published in the Journal of the American Medical Association in 2011 revealed a statistically significant increase in prostate cancer with vitamin E.
Though nothing is certain, scientists have also been looking at the following as possible preventers of prostate cancer.
Fruits, vegetables and whole grains. A plant-based diet tends to be low in fat, and dietary fat—especially the saturated fat found in animal food—may be linked to prostate cancer. Moreover, plant foods are rich in vitamins, minerals and various phytochemicals that may be beneficial. Many studies suggest that tomatoes are protective, possibly because they are rich in the carotenoid lycopene. And cruciferous vegetables such as broccoli, kale and cabbage contain compounds called indoles, which may inhibit the growth of prostate cancer cells. Still, it’s not clear which substances may be most important, so it’s best to vary your intake of fruits and vegetables.
Fatty fish. Prostate cancer is rare among Inuit men in Greenland, and researchers attribute this in large part to their high fish intake. In a 2003 Harvard study, men who ate the most fish were least likely to develop advanced prostate cancer (although fish oil supplements did not decrease the risk). A 2009 study reported that the greatest benefit was seen in men who ate fatty fish at least once a week and had a gene variant linked to an increased risk of prostate cancer. However, a 2013 study published in the Journal of the National Cancer Institute found that men with the highest blood levels of omega-3 fats from fish were at increased risk for prostate cancer. So the jury is still out.
Vitamin D. People who get little or no sun exposure tend to have higher rates of prostate cancer, and mortality rates for this cancer tend to be higher in northern regions, where there’s less sun. Many researchers believe that lack of vitamin D may be the explanation, since the skin makes this vitamin when exposed to sunlight. Similarly, dark-skinned people may be at higher risk for prostate cancer because their skin makes less D. Fortified milk is the major dietary source. The Institute of Medicine recommends 600 to 800 IU of vitamin D a day, but we recommend that most American adults take a daily supplement containing 800 to 1,000 IU, especially after age 60.
Soy and green tea. These are staples in most Asian diets and may be partly responsible for the lower rates of prostate cancer in Asia. For example, a review in the American Journal of Clinical Nutrition, which analyzed data from 14 studies, found that men who consumed soy regularly had a 26 percent reduced risk of prostate cancer, compared with those who ate little or none. However, the benefit was seen only with nonfermented soy foods (tofu and soymilk); fermented ones (miso and natto) showed neither benefit nor risk (there has been some concern that fermented foods may increase prostate cancer risk). The studies did not look at soy supplements, which are of questionable value. You should avoid soy supplements if you have kidney disease, a history of kidney stones or a family history of bladder cancer.