Benefits of fish oil including lowered blood pressure and reduced depression were shown by previous studies. New study suggests a link between fish oil and lowered risk of breast cancer, according to a preliminary study in Cancer Epidemiology, Biomarkers & Prevention.

Between 2000 and 2002, 35,016 postmenopausal women living in Washington State filled out 24-page questionnaires about their past and present supplement use, medical history, and overall health and lifestyle. At the study outset the participants did not have breast cancer. By the end of 2007, 880 of them (or about 2.5%) had developed breast cancer.

Women who reported taking fish oil at the start of the study had a 32% reduced risk of invasive ductal carcinoma of the breast, the most common form of breast cancer. The reduced risk was not shown to be associated with the less-common lobular breast cancer.

Other “specialty” supplements didn’t appear to be associated with breast cancer risk, including gingko biloba, soy, and St. John’s wort.

This is the first study to look specifically at the effects of fish oil supplements on cancer risk, said Emily White, Ph.D., who led the study conducted at Fred Hutchinson Cancer Research Center in Seattle, Washington.

"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.

Some research suggests that omega-3 fatty acids may reduce inflammation which, when prolonged, may increase the risk of cells becoming cancerous.

Other supplements with anti-inflammatory properties showed no significant links with risk of breast cancer.

White cautioned against recommending women to take fish oil supplements as a form of cancer prevention. "Theevidence is supportive, but not definitive," she said.

Further research on Omega-3 and Vitamin D and their impact on cancer, heart disease and stroke is currently underway at Harvard.