BETHESDA, Md. — A National Institutes of Health study published Tuesday in the Journal of the American Medical Association established a link between vitamin E supplementation and prostate cancer. Men who took 400 international units of vitamin E daily had more prostate cancers compared with men who took a placebo, according to an updated review of data from the Selenium and Vitamin E Cancer Prevention Trial, the NIH stated.
The findings showed that, per 1,000 men, there were 76 prostate cancers in men who took only vitamin E supplements versus 65 in men on placebo over a seven-year period, or 11 more cases of prostate cancer per 1,000 men. This represents a 17% increase in prostate cancers relative to those who took a placebo, the study noted.
"Based on these results and the results of large cardiovascular studies using vitamin E, there is no reason for men in the general population to take the dose of vitamin E used in SELECT (400 IUs) as the supplements have shown no benefit and some very real risks," stated Eric Klein, a study co-chair for SELECT and a physician at the Cleveland Clinic.
"Although ‘statistically significant’ to a statistician, one wonders if an absolute increase in the risk of prostate cancer of 1.6 cases per 1,000 person-years is really a ‘significantly increased risk of prostate cancer’ as noted in the article," countered Duffy MacKay, VP scientific and regulatory affairs for the Council for Responsible Nutrition.
“Men shouldn’t rush to judgment about vitamin E based on this study, but instead should consider the body of evidence, the amount being taken and their individual medical history," MacKay said. "Even with respect to prostate cancer, two other studies that were cited within the article produced different results — one demonstrated a 35% risk reduction for prostate cancer in men taking 50 mg (75 IU) vitamin E daily for six years and another resulted in no effect on risk."
"The study itself, in the confines of the drug model, appears to be well designed and well executed; however, it also evidences the risks of examining a nutrient in isolation," MacKay said. "With a reductionist approach to the benefits of nutrition, the study showed that a dose of 400 IU vitamin E was not likely to provide benefit for preventing cancer, and the authors found an increased risk for developing prostate cancer. Interestingly, when vitamin E was combined with selenium, the risk was reduced to a nonsignificant statistic, perhaps even the result of chance," he noted. "This reinforces the theory that vitamins work synergistically and that drug-like trials of nutrients, when used in isolation from other nutrients, may not be the most appropriate way to study them."
SWOG, an international network of research institutions, carried out SELECT at more than 400 clinical sites in the United States, Puerto Rico and Canada. SELECT was funded by the National Cancer Institute and other institutes that comprise the National Institutes of Health.
The SELECT study began in 2001 and included more than 35,000 men. It was started because earlier research had suggested that selenium or vitamin E might reduce the risk of developing prostate cancer. However, based on an independent safety monitoring review in autumn 2008, participants were told to stop taking their study supplements because it had become clear that the trial would never produce the 25% reduction in prostate cancer the study was designed to show with the use of these supplements. In 2010, the study sites were closed and more than half of the participants consented to have their health monitored via mail questionnaires. Now, 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 was undertaken to substantiate earlier, separate findings from studies in which prostate cancer risk was not the primary outcome. A 1998 study of male smokers in Finland who took 50 IU of vitamin E daily to prevent lung cancer showed 32% fewer prostate cancers in men who took the supplement. A 1996 study of men and women with a history of skin cancer who took selenium for prevention of disease recurrence showed that men who took the supplement had 52% fewer prostate cancers than men who did not take the supplement.
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. Other researchers are looking at single nucleotide polymorphisms, which are DNA changes known as SNPs, to see if a change in one or more genes could affect cancer risk or perhaps increase a man's risk of developing prostate cancer while taking vitamin E.
Except for skin cancer, prostate cancer is the most common type of cancer in men in the United States. The current lifetime risk of prostate cancer for American men is 16%. In 2011, there will be an estimated 240,890 new cases of prostate cancer and 33,720 deaths from this disease in the United States.
For questions about vitamin E, consumers should talk with their physician, nurse practitioner, pharmacist or other healthcare practitioner, MacKay suggested.