By Craig Weatherby
Breast cancer remains the most common form of cancer in women worldwide.
After lung cancer, it's the second most common cause of female cancer deaths.
Diet appears to affect cancer risk, with estimates suggesting that one-third of cases may be preventable through diet and lifestyle modification.
And growing evidence suggests that early exposure to omega-3 fatty acids from fish (DHA and EPA) may curb breast cancer risks (MacLennan M et al. 2010).
Conversely, diets high in omega-6 fats from vegetable oils appear to raise the risk … see “Breast Cancer and Omega-3s: More Encouraging Evidence” and “Breast Cancer Tied to Omega Imbalance … Again”.
Certain other compounds in seafood, including the vitamin D abundant in fatty fish, may be beneficial as well … see “Oyster Fats May Curb Breast Cancer”.
And it's pretty clear that selected food factors can help curb – or raise – the risk of breast cancer … see our sidebar, “Foods and breast risk”.
But epidemiological and lab studies can't prove that omega-3s help prevent breast cancer, and the results of the small number of human clinical studies have been inconsistent.
Now, a genetic study in mice suggests that a lifelong diet rich in omega-3 fatty acids can inhibit growth of breast tumors by 30 percent.
The authors said that their novel experiment is “the first to provide unequivocal evidence that omega-3s reduce cancer risk”. (UG 2013)
(A note of caution is in order. Although the study is encouraging, growing evidence indicates that outcomes in mice and humans do not always match.)
According to co-author David Ma from Canada's University of Guelph, “We show that lifelong exposure to omega-3s has a beneficial role [in mice] … what's important is that we have proven that omega-3s are the driving force and not something else.” (UG 2013)
As Dr. Ma noted, “There are inherent challenges in controlling and measuring diet in [clinical] studies … so we've used modern genetic tools to address a classic nutritional question.” (UG 2013)
Genetic study in mice strengthens the case for omega-3s
The study team included scientists from Dalhousie University, McGill University, and Harvard Medical School (MacLennan MB et al. 2013).
The U.S.-Canadian team created a novel transgenic mouse that develops aggressive mammary tumors … and produces omega-3 fatty acids.
They compared those animals to mice genetically engineered only to develop the same mammary tumors.
Mice producing omega-3s developed only two-thirds as many tumors … and the tumors were also 30 percent smaller compared to those in the control mice. “The difference can be solely attributed to the presence of omega-3s in the transgenic mice – that's significant,” Ma said (UG 2013).
We would agree, but also repeat our caution that rodent studies can only provide indications, not proof.
  • MacLennan M, Ma DW. Role of dietary fatty acids in mammary gland development and breast cancer. Breast Cancer Res. 2010;12(5):211. doi: 10.1186/bcr2646. Epub 2010 Oct 26. Review
  • MacLennan MB, Clarke SE, Perez K, Wood GA, Muller WJ, Kang JX, Ma DW. Mammary tumor development is directly inhibited by lifelong n-3 polyunsaturated fatty acids. J Nutr Biochem. 2013 Jan;24(1):388-95. doi: 10.1016/j.jnutbio.2012.08.002. Epub 2012 Sep 29.
  • University of Guelph (UG). Omega-3s Inhibit Breast Cancer Tumor Growth, U of G Study Finds. February 21, 2013. Accessed at
  • Yee LD, Young DC, Rosol TJ, Vanbuskirk AM, Clinton SK. Dietary (n-3) polyunsaturated fatty acids inhibit HER-2/neu-induced breast cancer in mice independently of the PPARgamma ligand rosiglitazone. J Nutr. 2005 May;135(5):983-8.