Unlike other studies, a new US trial claims that daily supplementation with high doses of vitamin E over years may increase the risk of developing prostate cancer.
In the randomized controlled trial, 35,533 healthy men 50 years or older from 427 study sites in the United States, Canada, and Puerto Rico were randomly assigned to receive selenium (200 micrograms/day), vitamin E (400 IU /day), both nutrients or placebo for a planned minimum of 7 years and maximum of
12 years (1). The researchers found that the rate of prostate cancer detection was greater in all supplemented groups when compared with placebo but was statistically significant only in the vitamin E group, with a 17% increase in rate of prostate cancer detection. Compared with the placebo group, in which 529 men developed prostate cancer, 620 men developed prostate cancer in the vitamin E group, as did 575 in the selenium group and 555 in the selenium plus vitamin E group.
According to the researchers, given that more than half the individuals 60 years or older consumed supplements containing vitamin E and 23% of those took at least 400 IU /day, despite a recommended daily dietary allowance of 22.4 IU for adult men, the implications of those observations were substantial. While an initial report of the Selenium and Vitamin E Cancer Prevention Trial (SELECT) in 2008 found no reduction prostate cancer risk in connection with either selenium or vitamin E supplements, the longer observation period in this trial indicated a significant increase in prostate cancer risk for the participants who had taken about 20-fold the recommended vitamin E dose for up to 10 years.
Experts commented that the results of this study are different from other large randomized intervention trials, which have demonstrated a 35% risk reduction for prostate cancer in men taking 50 mg (75 IU) vitamin E daily for a 6-year period (2) or no effect on prostate cancer risk for men taking 400 IU of vitamin E every other day for an median of 8 years (3). In light of these results, consumers would have no reason to stop using vitamin E supplements. They also pointed out that more commonly people do not even consume the Recommended Dietary Allowance (22.4 IU or 15 mg) and that overconsumption, by up to 400 IU as seen in the trial, is rather unusual.
In addition, the results would reinforce the theory that micronutrients work synergistically and that drug-like trials of nutrients, when used in isolation from other nutrients, in this case vitamin E, may not be the most appropriate way to study them. Overall, dietary supplements are commonly taken to help prevent deficiency-related diseases and it should not be expected, in and of themselves, and without the synergy of other healthy habits, to prevent chronic disease.
Lifetime risk of prostate cancer in the United States is currently estimated to be 16%. Although most cases are found at an early, curable stage, treatment is costly and urinary, sexual, and bowel-related adverse effects are common.