Vitamin E temporarily raises cancer risk

In a study of patients with head and neck cancer, use of vitamin E supplements was associated with an increased risk that their cancer would return or that they'd develop a new cancer.

However, during the second phase of the study when supplementation was discontinued, former vitamin E takers had a lower risk of cancer than their counterparts who had been given an inactive "placebo."

As a result, by the end of the 8-year study, both groups had comparable cancer risks, according to a report in the Journal of the National Cancer Institute.

"We were surprised by the findings," Dr. Francois Meyer, from Universite Laval in Quebec, Canada, told Reuters Health. "When we started the study, we had hoped that vitamin E supplementation would reduce or delay the risk of second primary cancer."

"If we would have stopped the study after the first phase, we might have concluded that vitamin E supplementation" had a true effect on cancer risk, Meyer noted. However, the fact that the elevated risk was not seen in the second phase suggests that such use may simply have had a screening effect - leading to earlier detection of cancers, he explained.

The findings are based on a study of 540 patients with head and neck cancer who were treated with radiation therapy and randomly selected to receive vitamin E, beta-carotene, or placebo for three years. Because the results of another trial had linked beta-carotene use with an increased risk of lung cancer, the beta-carotene arm of Meyer's study was stopped early due to ethical concerns.

During a follow-up period of around 52 months, 113 subjects developed new cancers and 119 developed recurrences of their old cancer.

As noted, the risk of cancer in each group depended on the phase of the study. During the treatment phase, vitamin E users were 86 percent more likely to develop cancer than placebo users. After treatment was stopped, former vitamin E users were 29 percent less likely to develop cancer compared with former placebo users.

"Usually, we say that people should weigh the pros and cons when considering a particular intervention," Meyer noted. "At the moment, there isn't much evidence supporting the use of high-dose antioxidants, (such as vitamin E), for long periods of time."

SOURCE: Journal of the National Cancer Institute, April 6, 2005.