Selenium and prostate cancer prevention

Dr. Krongrad points out that the media suggest that certain supplements “may” prevent prostate cancer. Using such jargon as “anti-oxidant,” the pitch plays on our emotions as we seek to stay healthy. There’s just one problem: the suggestions are without basis. Here he illustrates using the popular selenium as a proposed prostate cancer preventive as an example.

In 1996, my colleagues and I published a study of selenium supplements compared with placebo. We found that the men who got the selenium had more than 60 percent less prostate cancer than the men who got the placebo.

The study was problematic. First among the reasons was that we did not require prostate biopsy, without which you cannot know who has prostate cancer. This left open the possibility that the selenium merely disguised the cancer – by altering the signs of prostate cancer – without actually eliminating it. Secondly, the interval to the observed effect of cancer reduction seemed remarkably short for a slow growing cancer like prostate cancer. While our work was intriguing, it did not rigorously prove that selenium prevents cancer. None of that mattered as the media published our results and selenium was sold as something that “may” prevent prostate cancer.

There is a sequel to the story. Investigators at the National Cancer Institute (NCI) recently observed that men who used excessive amounts of multivitamins were at higher risk of advanced and fatal prostate cancer. Relying on data from nearly 300,000 men, the NCI study showed especially high associations with dietary supplementation with selenium, ß-carotene, or zinc. Heavy multivitamin users who also took selenium had an almost 6-fold increase in fatal prostate cancer.

The proposed role of selenium in prostate cancer prevention is being tested in a large study called SELECT. This study is due to mature in five years. For now, all we have are interesting but inconclusive data. Given the recent NCI report, it is quite possible that selenium not only does not prevent prostate cancer but that it actually accelerates prostate cancer. My advice? Eat a balanced diet and spend your money on something other than supplements.

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