Supplementation with the antioxidants vitamin E and beta carotene may cause unexpected problems in patients with head and neck cancer, researchers warn.

Reporting in the April 6 issue of the Journal of the National Cancer Institute, investigators at Laval University in Quebec City, Canada, studied 540 head and neck cancer patients who’d been treated with radiation therapy between 1994 and 2000.

The patients received supplementation with either a placebo, or vitamin E and beta carotene - a precursor of vitamin A - during radiation therapy and then for the following three years.

Although patients were tracked for an average of more than four years, beta carotene supplementation in this study was halted at one year after another trial found an increased risk of lung cancer among smokers who took the nutrient.

The researchers report that patients who received vitamin E supplements were at greater risk of developing a second primary cancer while receiving supplementation, as well as a lower risk of a second primary cancer after the end of supplementation, compared with patients who took a placebo.

Overall, after eight years, the proportion of patients who were free of a second primary cancer was similar in both groups, the study found.

Among the patients receiving vitamin E, the rate of recurrence of head and neck cancer or a second primary tumor was also higher during supplementation and lower after the end of supplementation, compared to patients taking a placebo.

“This cancer chemoprevention trial was conducted in a population of patients at high risk of second primary cancers. There is some concern about the generalization of the study results to individuals in the general population who are at low risk of a first primary cancer. Nevertheless, our results suggest that caution should be advised regarding the use of high-dose [vitamin E] supplements for cancer prevention,” the study authors wrote.