Vitamin E might raise risk of prostate cancer
Published Tuesday, October 11, 2011 4:55PM EDT
A large study launched to find out whether vitamin E supplements might help stave off prostate cancer has found just the opposite: the vitamin might actually raise the risk.
While the study can't say for sure if it was the vitamin that was raising the risk of cancer in these men, it's just the latest research to show that vitamin pills might not be the answer for fighting off cancer.
The study began in 2001, tracking some 35,000 men in the United States, Canada, and Puerto Rico over the age of 50 in a study dubbed SELECT (Selenium and Vitamin E Cancer Prevention Trial). The men were broken into four groups:
- a quarter were told to take 400 IU (international units) of vitamin E (dl-alpha tocopherol) a day
- a quarter took 200 micrograms of the mineral selenium a day
- a quarter took both
- and the fourth group took placebo pills
None of the men knew which supplement they were taking.
The researchers reported in December 2008 that the study had found neither selenium nor vitamin E supplements appeared to reduce the risk for prostate cancer. In fact, at that time, they also noticed a slightly increased risk of prostate cancer in those taking vitamin E alone. But they said the increase was "statistically non-significant."
All the men in the study stopped taking the pills in October 2008, but their health was still monitored. Since then, 521 more cases of prostate cancer have arisen, the authors report in the Journal of the American Medical Association:
- 147 case in the vitamin E group
- 143 in the selenium group
- 118 in the combination group
- 113 in the placebo group
The researchers say when they crunched the numbers, the vitamin E alone group had a 17 per cent increased rate of prostate cancer compared to the placebo group.
Dr. Joseph Chin, one of the authors of the study and a surgical oncologist at London Health Sciences Centre says that for men trying to avoid prostate cancer, vitamin E does not appear to be the way to go.
"Vitamin E is in fact not beneficial. When taken in large amounts to prevent prostate cancer, it may actually cause a slight bit of harm," he told CTV News.
Still, Chin said men who have taken vitamin E shouldn't be alarmed; the study showed that 700 men would have to take the vitamin daily for seven years in order for it to lead to one additional case of prostate cancer.
The study also noted there was not a statistically significant increased risk of prostate cancer in the vitamin E and selenium combo group, suggesting that selenium may have a protective effect by dampening the increased risk associated with vitamin E alone.
But what was troubling was that the higher risk from the vitamin E alone was still there even years after the men had stopped taking the vitamin -- suggesting the nutrient continues to have an effect on the body.
Doctors admit they don't know if or how vitamin E could be fuelling prostate cancers.
"A biological explanation for the observed increased risk of prostate cancer in the vitamin E arm is not apparent from these data," they write.
But the study results make their advice clear, says Dr. Robert Nam, the head of the Genitourinary Cancer Care Sunnybrook Research Institute in Toronto.
"It tells men they should stop taking high doses of vitamin E to prevent prostate cancer," he says.
The authors note that more than 50 per cent of people over the age of 60 take vitamin supplements containing vitamin E. About 23 per cent of them are taking at least 400 IU a day even though the current recommended daily allowance is only about 22 IU a day.
There are many forms of vitamin E; this study used dl-alpha-tocopheryl acetate, a synthetic form sold in capsule form. Some nutritional experts argue the synthetic form of is not the same as natural source vitamin E, and that the synthetic form is only half as active as natural-source vitamin E.
Lead author Dr. Eric Klein of the Cleveland Clinic says once again, the research is showing that more is not better when it comes to vitamin supplements.
"We have to not look at these as inert substances. They actually have a pharmacologic effects and that's important. So you have to be careful about what you take," he says.
The authors also say that their study underscores the need for consumers to be skeptical of health claims for dietary supplements, which are largely unregulated.
And they say it's also why careful, large-scale, randomized trials are needed to assess the benefits and harms of vitamin supplements.
With a report from CTV's Avis Favaro and producer Elizabeth St. Philip