Blog | Thursday, October 13, 2011

QD: News Every Day--Vitamin E supplements associated with prostate cancer risk

Men who took 400 international units (IU) of vitamin E daily had a 17% increased risk of developing prostate cancers compared to men who took a placebo, according to an updated review of data from the Selenium and Vitamin E Cancer Prevention Trial (SELECT).

Vitamin E crystal image courtesy of the National Cancer InstituteBased on these results and the results of large cardiovascular studies of vitamin E, there is no reason for men in the general population to take 400 IU of vitamin E, as the supplements have shown no benefit and some very real risks, said the study's lead author in a press release from the National Cancer Institute. Now, study participants are being followed for further outcomes.

The news comes a day after a separate study concluded that multivitamins were associated with increased total mortality in women, and that there was a dose-dependent relationship with iron supplements.

For the prostate cancer study, men from 427 study sites North America were randomized between August 2001 and June 2004. Eligibility criteria included a prostate-specific antigen (PSA) of 4.0 ng/mL or less, a digital rectal examination not suspicious for prostate cancer, and age 50 years or older for black men and 55 years or older for all others.

The primary analysis included 34,887 men who were randomly assigned to one of four treatment groups: 8,752 to get oral selenium (200 micrograms/d from L-selenomethionine) with matched vitamin E placebo; 8,737 to get vitamin E (400 IU/d of all rac-alpha-tocopheryl acetate) with matched selenium placebo; 8,702 to get both agents; and 8,696 to get both placebos. Follow-up was a minimum of 7 and maximum of 12 years. Results appeared Oct. 12, 2011, in the Journal of the American Medical Association.

In the placebo group, 529 men developed prostate cancer, compared to 620 men in the vitamin E group (hazard ratio [HR], 1.17; 99% confidence interval [CI], 1.004 to 1.36; P=.008); as did 575 in the selenium group (HR, 1.09; 99% CI, 0.93 to 1.27; P=.18), and 555 in the selenium plus vitamin E group (HR, 1.05; 99% CI, 0.89 to 1.22, P=.46). Compared with placebo, the absolute increase in risk of prostate cancer per 1,000 person-years was 1.6 for vitamin E, 0.8 for selenium, and 0.4 for the combination.

For every 1,000 men, there were 76 prostate cancers in men who took only vitamin E supplements, vs. 65 in men on placebo over a seven-year period, or 11 more cases.

An independent safety monitoring review in autumn 2008 ordered participants to stop taking their study supplements because the trial would never produce the 25% reduction in prostate cancer the study was designed to show. In 2010, study sites were closed and more than half of the participants consented to have their health monitored via mail questionnaires. Because of this latest finding, researchers are encouraging all participants to consider taking part in long-term study follow-up so investigators can continue to track outcomes.

SELECT researchers are now measuring the amount of vitamin E, selenium, and other nutrients in the blood of participants when they joined the trial, to see if the effect of the supplements depended upon this baseline level of micronutrient.