Alpha-tocopherol ( Vitamin-E ) supplementation produced unexpected adverse effects on the occurrence of second primary cancers and on cancer-free survival in patients with head and neck cancer, treated with radiation therapy.
Investigators at the Université Laval and Hotel-Dieu de Quebec's Oncology Research Centre, conducted a study among 540 patients 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.
Supplementation with Alpha-tocopherol ( 400 IU/day ) and Beta-carotene ( 30 mg/day ) or placebo began on the first day of radiation therapy and continued for 3 years after the end of radiation therapy.
In the course of the trial, Beta-carotene supplementation was discontinued after 156 patients had enrolled because of ethical concerns.
Another trial found an increased risk of lung cancer among smokers who took Beta-carotene.
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.
Canadian investigators evaluated the impact of vitamin E intake, in the form of a daily food supplement, among a population at high risk of developing a second tumor.
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 investigators' 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.
The results of this study suggest that caution should be advised regarding the use of high-dose Vitamin E supplements for cancer prevention.
Investigators 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.
The study was approved and funded by the National Cancer Institute of Canada.
Source: Journal of the National Cancer Institute, 2005