Fish Oil Linked to Lower Breast CA Risk

(MedPage Today) -- Fish oil could help prevent breast cancer, according to observational findings linking the supplements to lower breast cancer risk.

Women taking fish oil had a 32% reduced risk of breast cancer (95% confidence interval 8% to 50%) in a large cohort study led by Theodore M. Brasky, PhD, of Fred Hutchinson Cancer Research Center in Seattle.

Other "specialty" supplements didn't appear to either increase or decrease breast cancer risk, including phytoestrogens taken for menopausal symptoms (black cohosh and soy), Brasky's group reported online in Cancer Epidemiology, Biomarkers & Prevention.

Although fish oil deserves more study for prevention, the researchers cautioned against overinterpreting the results.

"Until these results are replicated, fish oil supplements should not be promoted for reduction of breast cancer risk," Brasky and colleagues wrote in the paper.

The concept is intriguing, agreed Sandhya Pruthi, MD, of the Mayo Clinic in Rochester, Minn., who has been involved with breast cancer chemoprevention studies using aromatase inhibitors as well as alternative therapies.

But "the findings from this study are definitely too early" to prompt individuals to take, or physicians to promote, fish oil for this purpose, she said in an e-mail. "A randomized, placebo-controlled study would be the next step in assessing the true benefit of fish oil in preventing breast cancer."

There is some support for a plausible link, the researchers said, since fish oil contains omega-3 polyunsaturated fatty acids that may reduce inflammation, which is linked to many steps in the development of cancer.

These fatty acids from fish have also been found in epidemiologic biomarker studies to be associated with reduced breast cancer risk.

The Vitamins and Lifestyle (VITAL) cohort study aimed to fill the lack of long-term prospective data on cancer risk associated with unregulated supplements.

The analysis looked only at nonvitamin, nonmineral "specialty" supplement use among 35,016 postmenopausal women ages 50 to 76 living in the western Washington state area covered by the Surveillance, Epidemiology, and End Results registry who completed the study's extensive survey.

During follow-up from 2000 through 2007 using the SEER cancer registry, 880 of the women developed incident invasive breast cancer.

Current users of fish oil supplements typically took it daily and appeared to carry a significantly lower breast cancer risk than nonusers (multivariable-adjusted hazard ratio 0.68, 95% CI 0.50 to 0.92).

But former use of fish oil didn't appear protective (HR 1.07, 95% CI 0.71 to 1.60). Average fish oil use over the 10 years prior to baseline suggested lower risk with use, but no clear trend emerged.

The researchers noted this difference might be explained "if use in the more distant past does not represent the exposure window of etiologic relevance."

They suggested that current use at baseline might be a surrogate for continued use after baseline, closer to the time of cancer incidence.

Although fish oil is most often taken for its cardiovascular properties, its use among those with a history of coronary artery disease actually appeared to increase the breast cancer risk compared with nonuse (HR 1.56 versus 0.84).

For women without a history of coronary artery disease, current fish oil use again appeared linked to lower breast cancer risk (HR 0.62, 95% CI 0.45 to 0.87).

There were no interactions with body mass index, use of nonsteroidal anti-inflammatory drugs, smoking status, or dietary arachidonic acid.

Unlike fish oil, other supplements with anti-inflammatory properties -- glucosamine, chondroitin, methylsulfonylmethane, and grapeseed -- showed no significant links or trends with risk of breast cancer.

Nor were there any significant associations between supplements taken to alleviate menopause symptoms and breast cancer risk. Compared with nonuse, the hazard ratios for regular use of at least once a week for at least a year were:

• 1.17 for black cohosh (95% CI 0.75 to 1.82)
• 1.27 for dong quai (95% CI 0.76 to 2.13)
• 1.01 for these combined with soy and St. John's wort (95% CI 0.80 to 1.27).

There also were no associations -- either averaged over 10 years or for former or current use -- with other specialty supplements, including acidophilus, coenzyme Q10, garlic pills, ginkgo biloba, ginseng, and melatonin.

The researchers cautioned that the study was limited by lack of information on dose, which is complicated by substantial variation in advertised versus actual dose, by lack of information on supplement use beyond the baseline survey, and by self-report on supplement use.

Also, the results could be due to chance because of the number of supplements analyzed, they noted.

The study was supported by grants from the National Cancer Institute.

The researchers reported no conflicts of interest.

Pruthi reported no conflicts of interest.

Primary source: Cancer Epidemiology, Biomarkers & Prevention Source reference: Brasky TM, et al "Specialty supplements and breast cancer risk in the VITamins And Lifestyle (VITAL) Cohort" Cancer Epidemiol Biomarkers Prev 2010; 19: OF1–13.