A new study has reported that consumption of omega-3 fats is associated with reduced breast cancer risk in obese (but not normal weight or overweight) Mexican women. Omega-3 polyunsaturated fatty acids are found in fatty fish such as salmon, mackerel and sardines, as well as walnuts, flaxseed oil and canola oil. The study also found that high intake of omega-6 fats is associated with inreased risk of breast cancer in premenopausal Mexican women. Omega-6 fats are found in vegetable oils such as corn oil, soybean oil, safflower oil, and sunflower oil.

The study was designed to investigate the relationship between consumption of omega-3 and omega-6 polyunsaturated fatty acids, body weight, and breast cancer risk among Mexican women. Consumption of omega-3 fats has been reported to have potential as a preventative strategy for reducing breast cancer risk. However, there is little data concerning omega-3 intake and risk of breast cancer in Mexican women. The study included 1,000 Mexican women with breast cancer and 1,074 cancer-free controls who were matched to the cases according to age at diagnosis, health-care system, and geographic region. In-person interviews were used to obtain information on health and diet. Measures of body mass index (BMI) were used to group women as normal weight (18.5 < BMI < 25), overweight (BMI 25 to 30) and obese (BMI > 30).

Increasing intake of omega-6 fats was found to be associate with increasing risk of breast cancer in premenopausal women. No significant association was found in the overall study group between omega-3 consumption and breast cancer risk. However, increasing omega-3 intake was found to be associated with reduced risk of breast cancer in obese women (but not in normal weight or in overweight women). The authors conclude that obesity might influence the association between omega-3 intake and breast cancer risk among Mexican women. The underlying mechanisms may be related to decreased inflammation and improved adipokin (signaling proteins secreted by adipose tissue) and estrogen levels induced by omega-3 polyunsaturated fatty acids in the fat tissue of obese women.

Omega-3 and omega-6 levels interact to influence breast cancer risk

While studies that have examined levels of consumption of omega-3 and omega-6 in the general population typically have not found associations with breast cancer risk, some patterns emerge when results are analyzed according to the ratio of omega-3 to omega-6 in the diet. High omega-3 to omega-6 ratios have been reported to protect against breast cancer risk, whereas low ratios increase risk. The study above adds to this body of knowledge with the findings that omega-3 fats may reduce the deterimental effects of obesity on breast cancer risk. Below is a summary of previous findings:

  • A French study found that women in the highest third of omega-3 to omega-6 in their breast fat tissue had lower risk of breast cancer than women in the highest third.
  • Another French study reported that the risk of breast cancer was inversely related to omega-3 consumption in women with the highest consumption of omega-6 fats.
  • A U.S. study reported that the highest compared with the lowest quartile of omega-3/omega-6 consumption was associated with a trend toward lower risk of breast cancer among premenopausal women.
  • A Chinese study found that women in the lowest third of consumption of marine omega-3 fats (from fish or shellfish) and the highest third of omega-6 fat consumption had double the risk of breast cancer of women who had the highest marine omega-3 fat intake and the lowest omega-6 fat intake.
  • A Singapore Chinese study reported that high dietary levels of marine omega-3 fatty acids were associated with reduced risk of breast cancer. Also, among women in the lowest quartile of marine omega-3 fatty acids, a significant increase in risk was observed in individuals belonging to the highest quartile of omega-6 fatty acid intake.
  • The omega-6 content of breast fat tissue of breast cancer cases was found to be significantly higher than that of cancer free women undergoing breast reduction surgery in a U.S. study.
  • A U.S. study reported that intake of marine fatty acids from food (but not from fish oil supplements) are associated with reduced risk of breast cancer recurrence.
  • Authors of a Spanish study concluded that a low omega-6/omega-3 ratio and elevated monounsaturated fatty acid levels (presumably from high olive oil consumption), the two prominent fat features of the Mediterranean diet, should be efficient at blocking HER2 expression in breast cancer cells.

Note that while fatty fish such as salmon are recommended to protect against breast cancer and its recurrence, recent research suggests that fish oil supplements should not be used during chemotherapy.