The study focused on the potential health benefits of 15 different so-called “specialty” supplements to see if they affect breast cancer risk, said study senior author Emily White, an epidemiologist at the Fred Hutchinson Cancer Research Center in Seattle.
“The only one that had an effect was fish oil,” she said.
Fish oil supplements, made from fatty fish such as salmon, contain high levels of omega-3 fatty acids.
In the study, White and her colleagues asked more than 35,000 Washington state women who were between the ages of 50 and 76 and all past menopause to answer questions about their use of “non-vitamin, non-mineral supplements.” All were participants in the Vitamins and Lifestyle (VITAL) cohort study, and none had a history of breast cancer.
After six years of follow-up, 880 cases of breast cancer were identified.
When the researchers looked at the women who took the fish oil supplements, they found they had a 32 percent reduced risk of breast cancer, which appeared to be restricted to invasive ductal breast cancer, the most common type.
The study was published in the July issue of Cancer Epidemiology, Biomarkers & Prevention, a journal of the American Association for Cancer Research.
White said that, while studies examining the link between consuming fish or omega-3 fatty acids and breast cancer risk have produced inconsistent results, this is the first study that suggested a connection between fish oil supplements and reduced breast cancer risk.
Other research has suggested that the omega-3 fatty acids found in fish may be heart-healthy.
White said it’s not clear how fish oil may protect against breast cancer, but it could have something to do with the anti-inflammatory properties of fish oil supplements.
She said the reduced risk was found in women who were taking fish oil supplements at the start of the study. She could not quantify the amount of fish oil supplements consumed, because “current use” was defined as any amount taken by a woman.
“Most women used it four to seven days a week. We don’t know how much,” she noted. But the typical supplement dose, she said, is about a third of a serving to the equivalent of a serving of fish a day.
White cautioned that she’s not recommending that fish oil supplements be taken for reducing breast cancer risk, and has issued a statement that “without confirming studies…we should not draw any conclusions about a causal relationship.” The study was “observational” only, and not a randomized trial that compared the use of fish oil with a group not using fish oil and the effect on cancer rates.
Eric Jacobs, strategic director of pharmacoepidemiology at the American Cancer Society, who reviewed the new study, called the research well designed. But, while it’s the first study to look at a link between fish oil supplements and breast cancer risk, more study is needed, he said.
“The lower risk of breast cancer among women taking fish oil supplements could be due to chance,” Jacobs said.
White agreed that more study is needed. Such research is about to start, she said, with Harvard researchers enrolling participants to look at the impact of omega-3 fatty acids and vitamin D on the risk of cancer, heart disease and stroke.
For more information visit the American Cancer Society