A recent report in Cancer Epidemiology, Biomarkers & Prevention, a journal of the American Association for Cancer Research, adds to the growing evidence that fish oil supplements may play a role in preventing chronic disease.

Researchers at the Fred Hutchinson Cancer Research Center in Seattle, Wash., led by Emily White, Ph.D., a member of the public health sciences division, asked 35,016 postmenopausal women who did not have a history of breast cancer to complete a 24-page questionnaire about their use of non-vitamin, non-mineral "specialty" supplements in the Vitamins and Lifestyle (VITAL) cohort study.

After six years of follow-up, 880 cases of breast cancer were identified using the Surveillance, Epidemiology and End Results registry.

Regular use of fish oil supplements, which contain high levels of the omega-3 fatty acids, EPA and DHA, was linked with a 32 percent reduced risk of breast cancer. The reduction in risk appeared to be restricted to invasive ductal breast cancer, the most common type of the disease.

The use of other specialty supplements, many of which are commonly taken by women to treat symptoms of menopause, was not associated with breast cancer risk.

This research is the first to demonstrate a link between the use of fish oil supplements and a reduction in breast cancer. Studies of dietary intake of fish or omega-3 fatty acids have not been consistent.

"It may be that the amount of omega-3 fatty acids in fish oil supplements are higher than most people would typically get from their diet," White said.

However, White cautioned against gleaning any recommendations from the results of one study.

"Without confirming studies specifically addressing this," she said, "we should not draw any conclusions about a causal relationship."

Edward Giovannucci, M.D., Sc.D., professor of nutrition and epidemiology at the Harvard School of Public Health and an editorial board member of Cancer Epidemiology, Biomarkers & Prevention, agreed.

"It is very rare that a single study should be used to make a broad recommendation," said Giovannucci. "Over a period of time, as the studies confirm each other, we can start to make recommendations."

Still, fish oil continues to excite many, as evidence emerges about its protective effect on cardiovascular disease and now cancer.

Harvard researchers are currently enrolling patients for the randomized Vitamin D and Omega-3 Trial (also called VITAL), which will assess the impact of fish oil supplements and vitamin D on cancer, heart disease and stroke.

The researchers plan to enroll 20,000 U.S. men aged 60 years and older and women aged 65 years and older who do not have a history of these diseases and have never taken supplements.