Fish oil supplements may lower the risk of breast cancer by 32%, according to a recent study. No other common non-vitamin, non-mineral supplement was found to influence breast cancer risk.
The study, led by researchers at the Fred Hutchinson Cancer Research Center, was published last week in Cancer Epidemiology, Biomarkers & Prevention. It analysed data collected between 2000 and 2002 from 35,000 Washington State women between the ages of 50 and 76, all past menopause, in the form of self-reported questionnaires. Data collected focused on the use of non-vitamin, non-mineral supplements. None of the participants had a history of breast cancer. The authors followed participants for an average of 6 years (through 2007), during which they identified 880 cases of breast cancer.
Correlating incidence of breast cancer with the use of supplements, the researchers found that the use of fish oil supplements was associated with a 32% lower risk of breast cancer, and that no other supplement was associated with breast cancer risk. Breast cancer has two major types, attacking primarily milk ducts and milk glands - interestingly, fish oil supplements were specifically associated with lower risk of ductal carcinoma (the most common form of breast cancer) only. Fish oil supplements were also found to be associated with a lower risk of colorectal cancer. Daily current use of fish oils was found to be the key association, while past use of fish oils did not appear to have protective properties. The survey did not collect information on doses.
The following supplements were found not to be associated with breast cancer risk: acidophilus, black cohosh
How would fish oils protect from breast cancer? Fish oils contain Omega-3 fatty acids including EHA and DHA, which are known for their anti-inflammatory properties. "There is pretty of good evidence that inflammation is involved in cancer and fish oil [may act as] an anti-inflammatory drug,” says Dr. Emily White, the lead author for the study. Omega-3 fatty acids have been associated, in past studies, with benefits in cardio-vascular health.
How significant is this study? The study was well received: “short of a randomized trial, this is as about as well as you can do," says Timothy Rebbeck, an epidemiologist at the University of Pennsylvania in Philadelphia. Other studies in the past have not found a link between fish oils and breast cancer, but this may be because supplements represent a higher amount of fish oils than those included in a regular diet, suggests Emily White.
The study does have limitations due to its very design. Emily White cautions: "without confirming studies specifically addressing this we should not draw any conclusions about a causal relationship." Eric Jacobs, director for pharmacoepidemiology at the American Cancer Society, calls the study "well designed," but adds: "the lower risk of breast cancer among women taking fish oil supplements could be due to chance." Because this is an observational cohort study, meaning that it analyzes patterns post facto, it cannot with certainty determine causality, which can only be determined by causal double blind studies, where participants are randomly assigned fish oil supplements or placebos. Researchers from Harvard University are now in the process of launching such of clinical study, the results of which will only be available in 5 to 10 years.
Should you take fish oil supplements? "There is some limited evidence from my study and others that fish oil may be good for preventing breast cancer, but there is not sufficient evidence to make a public health recommendation right now," says Emily White. Dr. Edward Giovannucci, of the Harvard School of Public Health, agrees: "it is very rare that a single study should be used to make a broad recommendation." On the other hand, if you already take fish oil supplements, you now have another reason to feel good about it. Be aware, however, that this study specifically tags fish oil supplements, and that other sources of Omega-3 fatty acids, such as flax seed, which carries primarily ALA fatty acids, may not be endowed with the same benefits.
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