Fish Oil May Lower Risk for Breast Cancer in Postmenopausal Women

July 12, 2010 — Fish oil supplement intake is associated with a lower risk for breast cancer in postmenopausal women, according to the results of the VITamins And Lifestyle (VITAL) Cohort study reported in the July issue of Cancer Epidemiology, Biomarkers & Prevention.
"Use of nonvitamin, nonmineral 'specialty' supplements has increased substantially over recent decades," write Theodore M. Brasky, from Hutchinson Cancer Research Center, University of Washington in Seattle, and colleagues. "Several supplements may have anti-inflammatory or anticancer properties. Additionally, supplements taken for symptoms of menopause have been associated with reduced risk of breast cancer in two case-control studies [but] there have been no prospective studies of the association between the long-term use of these supplements and breast cancer risk."
At baseline in 2000 to 2002, a total of 35,016 postmenopausal women, aged 50 to 76 years and living in western Washington State, completed a 24-page questionnaire concerning their use of specialty supplements. Use was characterized by recency (current vs past), frequency (days/week), and duration (number of years). The Surveillance, Epidemiology, and End Results (SEER) registry showed that from 2000 to 2007, there were 880 incident invasive breast cancers. Cox proportional hazards models allowed estimation of multivariable-adjusted hazard ratios (HRs) and 95% confidence intervals (CIs).
For ductal, but not lobular, cancers, current use of fish oil was associated with a reduced risk for breast cancer (HR, 0.68; 95% CI, 0.50 - 0.92), and 10-year average use suggested a trend toward a lower risk (P = .09). Use of the other specialty supplements, including those sometimes taken for menopausal symptoms (black cohosh, dong quai, soy, or St. John's wort) was not associated with breast cancer risk.
"Fish oil may be inversely associated with breast cancer risk," the study authors write. "Fish oil is a potential candidate for chemoprevention studies. Until that time, it is not recommended for individual use for breast cancer prevention."
Limitations of this study include lack of data on supplement dose, reliance on self-report, lack of updated exposure information after baseline, power limited by the relatively low prevalence of use of some specialty supplements, and the possibility of chance findings because 15 specialty supplements were examined.
"[T]his is the first prospective study to report on the association of specialty supplements with breast cancer risk," the study authors conclude. "Our finding of a reduced risk of breast cancer with use of fish oil warrants further study of this agent, focused particularly on timing of exposure and dose, as well as on mechanisms of action that might explain differences by tumor stage or histologic type."
The National Institutes of Health, National Cancer Institute supported this study. The study authors have disclosed no relevant financial relationships.
Cancer Epidemiol Biomarkers Prev. 2010;19:1696-1708. Abstract