NPA Notes Limitations of JNCI Study on Vitamin C and E on Cancer Incidence in Women

A new study published Tuesday, December 30, in The Journal of the National Cancer Institute (JNCI), suggests that long-term dietary supplementation with any combination of the antioxidants vitamin C, vitamin E, or beta carotene does not reduce the risk of cancer or the risk of dying from cancer in women already at an elevated risk for cardiovascular disease.

This study, titled the Women's Antioxidant Cardiovascular Study, was a double-blind, placebo-controlled 2 x 2 x 2 factorial trial of vitamin C (500 milligrams (mg) of ascorbic acid daily), natural-source vitamin E (600 IU of alpha-tocopherol every other day), and beta carotene (50 mg every other day). Participants were 7,627 women who were free of cancer, but who were at increased risk for cardiovascular disease, before being randomly assigned for this study.

After analysis of the study, Daniel Fabricant, Ph.D. the Natural Products Association’s vice president of scientific and regulatory affairs, reported that despite being placebo controlled, the study did not account for intake of the antioxidant nutrients in the diet, a potential confounder as indicated by one of the study's authors, Jennifer Lin, Ph.D., an assistant professor of medicine at Harvard Medical School, who stated that "that they [the antioxidants] might be effective in people who are poorly nourished, but not in well-nourished people such as the women in the study."

It is important to note that previous Centers for Disease Control data regarding its “5-A-Day” program, demonstrated that only 23 percent of Americans eat the recommended five daily servings of fruits and vegetables, those fruits and vegetables being the primary dietary source of antioxidants like vitamins C, E and beta-carotene. Additionally, the study authors recognize that the study had very limited statistical power to investigate any effect of dietary antioxidants on the risk of specific cancers; more research is needed due to previous epidemiological studies that have shown a benefit of antioxidants in cancer prevention.

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