Two large-scale clinical trials found that vitamin E, vitamin C or selenium supplements don’t reduce the risk of prostate cancer or other cancers in older men.
Previous studies had suggested that vitamin E or selenium supplements might reduce prostate cancer risk. Smaller studies also hinted that vitamin C might help to prevent prostate and other cancers.
NIH-funded researchers tested how prostate cancer and total cancer risk is affected by the dietary supplements. One research group recruited more than 35,000 men, age 50 and older, who had no evidence of prostate cancer. The men were randomly assigned to receive selenium, vitamin E, both or inactive placebo pills.
The study was cut short in late 2008, after an average follow-up of about 5.5 years. That’s because the supplements seemed to offer no cancer-related benefits.
The second trial looked at vitamin E and C supplements. More than 14,000 male doctors, age 50 or older, were randomly assigned to take either vitamin E, vitamin C, both or a placebo. After an average follow-up of about 8 years, neither vitamin—alone or in combination—significantly reduced the risk of prostate or other cancers compared to the placebo group.
Dietary supplements can often seem beneficial in small studies. The new studies highlight the fact that large, carefully controlled trials are needed to test whether they really live up to their hoped-for benefits.