Adding to the wave of anti-supplementational multivitamins and minerals research is a study conducted by the Fred Hutchinson Cancer Research Center in collaboration with researchers from institutions including the University of Texas Health Science Center at San Antonio. Published by the Journal of the National Cancer Institute, the study determined hazard ratios for the development of prostate cancer due to supplementation with selenium and vitamin E. The work was motivated by the outcome of the Selenium and Vitamin E Cancer Prevention Trial (SELECT) initiated by the U.S. National Cancer Institute in 2001: the trial was evaluating whether selenium, vitamin E, or both could reduce prostate cancer risk, but was ended three years early because interim analyses predicted low benefits from supplementation and showed a modest increase in prostate cancer risk from vitamin E alone. Two years later, the subjects who had received high-dose Vitamin E (400 IU/day) a significant 17% increased risk of developing prostate cancer.
The study at hand examined two hypotheses related to SELECT outcomes: 1) “High selenium status at baseline was associated with reduced cancer risk among men receiving placebo supplements,” and 2) “Selenium supplementation reduced cancer risk among men with low selenium status at baseline.” Additionally, the researchers tested a posteriori hypothesis motivated by the Nutritional Prevention of Cancer Trial (NPC) “that vitamin E supplementation increased prostate cancer risk among me with low selenium status at baseline.” Data came from 1739 toenail samples of men in SELECT. Baseline selenium status was measured, and after grouping data into quintiles of toenail selenium, the researchers made a number of comparisons to determine the factors that may have led to an increased risk of developing prostate cancer.
Among men with high selenium status at baseline, selenium supplementation increased risk by 91% compared to men with lower selenium status at baseline; it seems that selenium levels had increased to a toxic level through supplementation. This risk was increased to 124% in men who had baseline selenium levels in the 60th percentile and received both selenium and vitamin E supplementation. However, when men received vitamin E supplementation alone, there was no effect on men with high baseline toenail selenium, but there was a statistical increase in risk for men with a baseline level in the second quintile.
These results add to the confusion among general consumers. “Many people think that dietary supplements are helpful or at the least innocuous. This is not true,” asserted lead author Alan Kristal, Ph.D., at the Publich Health Sciences Division of Fred Hutchinson. “We know from several other studies that some high-dose dietary supplements–that is, supplements that provide far more than the daily recommended intakes of micronutrients–increase cancer risk. We knew this based on randomized, controlled, double-blinded studies for folate and beta carotene, and now we know it for vitamin E and selenium.” Essentially, there was no apparent benefit of selenium and vitamin E related to prostate cancer risk, and for some patients, supplementation was actually harmful. Dr. Kristal recommends that “men using these supplements should stop, period.”
This work was supported in part by Public Health Service Cooperative Agreement grant U10 CA037429 awarded by the National Cancer Institute, Division of Cancer Prevention, National Institutes of Health, Department of Health and Human Services, and by the National Center for Complementary and Alternative Medicine (National Institutes of Health) . Study agents and packaging were provided by Sabinsa Corporation (Piscataway, NJ), Tishcon Corporation (Westbury, NY), and DSM Nutritional Products Inc (Parsipanny, NJ). Optional study multivitamins were provided by Perrigo Company (Allegan, MI).