Beta carotene, vitamin C and vitamin E supplements taken for years failed to lower overall cancer risk in the latest study to cast doubt on the possibility that such dietary supplements can prevent cancer.
The findings, published on Tuesday in the Journal of the National Cancer Institute, followed two other important studies that also did not show that various antioxidant supplements could prevent cancer.
"Although a healthful dietary pattern rich in fruits and vegetables may lower cancer risk, such benefits cannot be mimicked by simply popping a few vitamin supplements," Dr. JoAnn Manson of Brigham and Women's Hospital and Harvard Medical School in Boston said in a statement.
Manson, Jennifer Lin and colleagues tracked 7,627 women who were an average 60 years old at the start of the study, who took supplements for about 9-1/2 years.
Some took 500 milligrams of vitamin C daily, 600 IU (international units) of vitamin E every other day or 50 milligrams of beta carotene every other day — or various combinations of the three supplements. Others were given placebos.
Women who took the supplements had similar rates of cancer and cancer death compared to those who took a placebo, the researchers said. The study suggested that vitamin E supplements might reduce colon cancer risk and that beta carotene supplements might modestly raise lung cancer risk.
The researchers, however, acknowledged that while the women took the supplements for almost a decade, the study "may still be of insufficient duration to assess effects on cancer incidence, given the long latency for cancer."
"Simply taking antioxidant supplements is insufficient to prevent cancer. People should take more natural plant foods which are rich with many nutrients including but not limited to antioxidants," Lin said by e-mail.
Beta carotene, vitamin E and vitamin C are antioxidants thought to protect against damage caused by free radicals, substances that can harm cells, tissues and organs.
Fruits and vegetables are rich in these vitamins, and it has been shown that people who eat plenty of these foods have a lower risk of heart disease, cancer and other conditions.
The Council for Responsible Nutrition, a dietary supplement industry group, found fault with the study.
Andrew Shao, the group's vice president for scientific and regulatory affairs, noted in a telephone interview that the women in the study all were at high risk for heart disease, and the study's original design was to assess whether the supplements protected against cardiovascular illness.
"Supplements are just one tool that people need to incorporate into their lifestyle to stay healthy. We can't expect just to take supplements and that's going to prevent cancer. That simply isn't the way it works," Shao added.
In a study released in November involving about 15,000 male doctors, vitamin E and C supplements did not lower cancer risk. Another study released in October found no cancer reduction in 35,000 men taking vitamin E and selenium supplements.