High vitamin E doses cited as cancer risk
As many as half of American men take supplements containing vitamin E, yet that practice could be increasing their risk of prostate cancer. A landmark clinical trial involving more than 35,000 men found that those who were randomly given vitamin E supplements had a 17 percent greater likelihood of developing prostate cancer after seven to 10 years of follow-up compared with those who were randomly given placebos.
The study, published in today’s Journal of the American Medical Association, underscores the importance of clinical trials in evaluating the usefulness of dietary supplements -- especially when given in doses far higher than the recommended daily allowance. The daily dose of vitamin E given in the study was 400 international units, nearly 20 times greater than the RDA of 22.4 IU for adult men.
An estimated one in four American men currently take this higher dose of vitamin E, a practice that the study researchers believe should change based on the new results . “This is the highest level of scientific evidence that we have concerning vitamin E,” said study leader Dr. Eric Klein, chair of the Cleveland Clinic’s Glickman Urological and Kidney Institute. “We now know it doesn’t prevent common disease and that it may be harmful. It’s hard to come up with a rationale for why a healthy person would want to take it.”
Klein said he was surprised by the study findings, which also found that selenium supplements and a combination of selenium and vitamin E posed no greater prostate cancer risk. The study’s initial results, published in 2009, indicated that vitamin E, selenium, and the two in combination might increase the likelihood of prostate cancer, as well as diabetes, but none of those results were statistically significant.
The latest findings, which followed study participants for an additional two years after they stopped taking the supplements, found an increase in prostate cancer only in the vitamin E takers and found no increase in diabetes risk. Some 76 prostate cancers were diagnosed for every 1,000 men who took vitamin E supplements compared with 65 prostate cancers for every 1,000 men who took placebos.
That’s a pretty low increase in absolute risk, but Klein was concerned that the men’s cancer risk continued to rise for years after they stopped taking the supplement.
Other experts had already been warning patients off vitamin E. “I’d been discouraging it in my practice for years,” said Dr. Philip Kantoff, who treats prostate cancer patients at the Dana-Farber Cancer Institute in Boston. Older studies suggesting a benefit from vitamin E, he added, were “based on minimal data.”
The exact role vitamin E might play in triggering prostate cancer, however, remains unknown. Kantoff said it’s possible that certain genes could be involved in determining how the body uses vitamin E -- an antioxidant that, in laboratory studies, has been shown to actually thwart cancer cells.
Klein said more research is needed into vitamin E’s mode of action but emphasized that “supplements are biologically active agents like drugs , and we need to treat them that way.”
Coincidentally, another headline-provoking study published yesterday suggested that women who took multivitamins, iron, or other dietary supplements faced a higher risk of dying than those who skipped them.
All of this accumulating evidence could prompt doctors to change their conventional wisdom when it comes to telling patients to take a multivitamin/mineral “just to be on the safe side.” Klein thinks the new advice should be that if you’re following a fairly balanced diet, you’re better off skipping the supplements.