Taking high-dose vitamin E supplements for an extended period doesn't protect against cancer; in fact, it may even speed up the development of latent cancers, according to a study by researchers from Hotel-Dieu de Quebec Research Centre and Universite Laval. Their results are published in the April issue of the prestigious Journal of the National Cancer Institute.
Dr. Isabelle Bairati, professor at the Universite Laval Faculty of Medicine and researcher at Hotel-Dieu de Quebec's Oncology Research Centre, and colleagues conducted the study among 540 volunteers over an eight-year period. All the participants were treated for early stage head and neck cancer and were at high risk of developing another cancer. During the first three years, half of the participants received 400 international units of vitamin E daily, while the rest were given a placebo.
Researchers put forth an initial hypothesis that people who eat a lot of fruits and vegetables are less likely to develop cancer. This beneficial effect might come from the many antioxidant vitamins contained in those types of foods. Dr. Bairati and her colleagues thus decided to analyze the impact of vitamin E intake, in the form of a daily food supplement, among a population at high risk of developing a second cancer.
The main results were as follows:
- In the three years during which participants were given either vitamin E supplements or a placebo, researchers recorded more cancer cases in the vitamin E group than in the placebo group. In the vitamin E group, 20% of participants developed cancer as opposed to only 10% in the placebo group. The expected protective effect of vitamin E was thus disproved.
In the period after the supplements were stopped, the situation was reversed: more cancer cases were recorded in the placebo group than in the vitamin E group.
At the end of the eight-year period, the percentage of patients who developed cancer was the same in both groups (30%).
Researchers suggest that the use of vitamin E supplements may have sped up the development of latent cancers in the patients who were part of the vitamin E group.
Although these results may appear surprising when compared to the researchers' initial hypothesis, they are consistent with other recent studies indicating that vitamin E, in the form of a food supplement, may have adverse effects on health. "This cancer chemoprevention trial was conducted in a population of patients at high risk of second 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 cancer. Nevertheless, our results suggest that caution should be advised regarding the use of high-dose vitamin E supplements for cancer prevention," explained Dr. Bairati.
Dr. Bairati and her colleagues thus advise caution in the use of high- dose vitamin E supplements for an extended period, and recommend instead a balanced diet including at least five servings of fruits and vegetables a day.
Dr. Bairati's study was approved and funded by the National Cancer Institute of Canada. It was also approved by Health Canada and ethics committees from each of the participating hospitals.