Taking vitamin E supplements may harm men's health, according to a new study that suggests the supplements can significantly increase the risk of prostate cancer.
The findings come from the large Selenium and Vitamin E Cancer Prevention Trial, otherwise known as the SELECT study, the initial results of which were published in 2008. Designed to test evidence indicating that selenium (a trace mineral found primarily in plants as well as some meats and seafood) and vitamin E (an antioxidant found in vegetable oils and nuts) might lessen prostate risk, the study found that there was, in fact, no reduction.
The updated results, published Tuesday in the Journal of the Medical Association, take that finding one step further.
They show that study participants receiving vitamin E had a 17 percent increased risk of prostate cancer, which, according to the Centers for Disease Control, is the second-most common cancer among men in the U.S.
"The observed 17 percent increase in prostate cancer incidence demonstrates the potential for seemingly innocuous yet biologically active substances such as vitamins to cause harm," the study's authors write.
The latest report does not offer any reason why vitamin E supplements may be tied with increased prostate cancer risk.
"This was a surprising finding and, at present, there is no biological explanation for why those who took vitamin E are at higher risk of developing prostate cancer," Dr. Eric Klein, chairman of the Glickman Urological and Kidney Institute at the Cleveland Clinic and the study's lead author, told HuffPost. He added that the trial data have been made available to the wider scientific community, in the hopes that additional research will be conducted to better understand the current findings.
This is not the only time in recent years that the use of vitamin supplements has been called into question.
In 2003, the U.S. Preventive Services Task Force concluded there was insufficient evidence to recommend either for or against the use of vitamin A, C or E supplements in preventing cancer and cardiovascular disease. And as MSNBC reported on Monday, the Archives of Internal Medicine has released a study suggesting dietary supplements may be tied to increased risk of death among older women.
The SELECT study did not look at the potential impact of generally available multivitamins on prostate cancer risk. Participants in the trial were given a relatively high dose of 400 IU per day, whereas multivitamins tend to have approximately 22.5 to 60 IU.
Nonetheless, Klein expressed his personal belief that the potential risks of vitamin E supplements are such that he sees no reason for otherwise healthy men to take them. "As we point out in the paper, there are few, if any, studies that show any health benefits for taking vitamin E, and the SELECT findings suggest it could be harmful," he said.
Dr. Edward Messing, chairman of the department of urology at the University of Rochester's Medical Center, cautioned that the study's findings should be kept in perspective. Despite the apparent increased risk of prostate cancer, the number of participants who actually developed the disease was still relatively small. He said future research might want to look at the potential benefit of other forms of vitamin E, which have been shown to be effective preventative agents in nonhuman studies.
In the meantime, Messing said, it serves as a reminder that men should think carefully before taking any supplements.
"As a demonstration that natural vitamins can actually be harmful and that men should not be taking vitamin E 'by the bagful' just because it's 'natural' … [that] seems like a very important message," Messing said. "Even vitamins can have real toxicities."