The researchers presented their findings at the 7th Annual International Conference on Frontiers in Cancer Prevention Research hosted by the American Association for Cancer Research (AACR) and taking place in National Harbor, Maryland, this week.
The study was led by Drs Howard D Sesso, and Dr J Michael Gaziano, both assistant professors of medicine at Brigham and Women’s Hospital, a teaching affiliate of Harvard Medical School in Boston, Massachusetts. Gaziano is also assistant professor of medicine at Veteran Affairs (VA) Boston.
“After nearly 10 years of supplementation with either vitamin E or vitamin C, we found no evidence supporting the use of either supplement in the prevention of cancer,” said Sesso, explaining that while the two vitamins did not show any benefits compared with placebo, they also caused no harm.
The findings come from the Physicians’ Health Study II (PHS-II), a randomized clinical trial involving over 14,500 male physicians who were aged 50 and over at the start of the trial in 1997.
At least half of adult Americans take vitamin supplements in the belief that they help to prevent chronic diseases, but the reality is there is no adequate evidence from long term randomized studies to support this.
The PHS-II was set up to address this research gap. The study as a whole examines four of the most popular supplements taken by adults in the US: vitamin C, vitamin E, beta-carotene, and multivitamins, and tests their effect on primary prevention of cardiovascular disease, total cancer, and prostate cancer. The trial also looked at the effect of these supplements on colon polyps and colon cancer, cataract, macular degeneration, and early cognitive decline.
For this part of the study the participants were randomly assigned to take 400 IU of vitamin E every other day (or its placebo), or to take 500 mg of vitamin C every day (or its placebo).
The participants were followed for up to 10 years during which time they also completed annual questionnaires.
The researchers said the results showed that vitamin E did not have a significant effect on prostate cancer, and both vitamin E and vitamin C showed a similar lack of effect on cancer overall.
Sesso and Gaziano said previous studies of laboratory and observational research that showed people on a diet rich in vitamins E and C had a lower risk of cancer had suggested taking these vitamins as supplements may have the same effect. But Gaziano said that this long term study showed that:
“Individual vitamin supplements such as vitamin E and C do not appear to provide the same potential advantages as vitamins included as part of a healthy, balanced diet.”
Sesso said these findings are clinically important because very few studies have tested this effect. The trial on the daily multivitamin supplement is still ongoing said Sesso.
The reseachers did not mention whether the study will be written up as a peer-reviewed journal paper.
The cardiovascular outcomes of the PHS-II study were reported recently in the Journal of the American Medical Association, JAMA. Click here for a summary of that study: “Two Antioxidant Vitamins Don’t Protect Against Heart Disease”.
Sources: AACR press release, PHS II website.
Written by: Catharine Paddock, PhD