In the large Women's Antioxidant Cardiovascular Study, participants who took beta carotene, vitamin C, vitamin E, or a combination of supplements had no significant reductions in their risk of cancer.
The clinical trial, which involved 7,627 women who were followed for an average of 9.4 years, was conducted by Dr. Jennifer Lin and colleagues at Harvard Medical School in Boston, and is published in the Journal of the National Cancer Institute.
The patients were randomly assigned to a placebo group, or to 500 mg ascorbic acid daily, 600 IU alpha-tocopherol every other day or 50 mg beta-carotene every other day. Overall, 624 women developed invasive cancers and 176 died from their disease.
Compared with women who took placebo, the relative risk of developing cancer was almost identical in the vitamin C group, the vitamin E group and the beta carotene group.
There was also little difference of dying from cancer in any of the groups. The risk increased by 28 percent in women who took vitamin C, decreased by 13 percent in those who took vitamin E, and decreased by 16 percent in the beta carotene group.
"We observed no overall associations of the three antioxidant supplements, taken singly or combined, with total cancer incidence or mortality. Duration of supplementation also did not appear to alter the associations of these supplements with risk of cancer or mortality due to cancer," Lin and her colleagues write.
The findings "suggest that there are no overall benefits or risks of vitamins C and E and beta carotene supplementation in the primary prevention of total cancer incidence or cancer mortality," the authors conclude.
Dr. Demetrius Albanes of the National Cancer Institute in Bethesda, Maryland notes in an editorial that despite the lack of overall benefits with antioxidants, two of the study's findings "deserve additional mention." First, there was a trend toward protection against colorectal cancer with vitamin E supplementation. Second, there was an elevated lung cancer risk in the women who took beta carotene supplements.
Albanes adds that clinical trials with negative results or those with outcomes that are unexpected are not failures; "they have and will continue to shed light on the causes of cancer and help us discover the means for its prevention."
SOURCE: Journal of the National Cancer Institute, January 7, 2009.
