Japanese and French studies support omega-3s' preventive potential; findings finger omega-6 excess as risk factor
Experiments in human cancer cells and in animals offer very strong indications that omega-3s discourage the growth of common cancers.
And there have been a number of epidemiogical studies that examined the possible preventive effects of omega-3s against breast cancer, with mixed but generally positive results.
(To see previous reports, search our newsletter archive for “breast”.)
As the authors of a new Japanese put it, “In contrast to [positive] results from laboratory studies… protective effects for breast cancer have proved equivocal in epidemiological studies.”
(In epidemiogical studies, researchers look for associations between people's diets or lifestyles and the prevalence of specific diseases.)
Epidemiogical studies cannot prove a cause-and-effect connection between a food or food factor and the risk of a disease.
But consistent results from a series of studies provide strong indications of the potential for a food or food factor to prevent or cause a disease.
In a new “case-control” epidemiogical study from Japan, researchers compared the blood levels of omega-3s in breast cancer patients with the blood levels of omega-3s in healthy controls.
The results lend further weight to the hypothesis that omega-3s help prevent breast cancer.
And the results from a French study published in 2002—which we discovered while researching this report—suggest that a shortage of omega-3s and excess of omega-6 fatty acids in a woman's diet may be a contributing risk factor.
Japanese study affirms preventive potential of omega-3s
Scientists at the Aichi Cancer Center Research Institute in Nagoya, Japan collected dietary information and blood samples from 103 breast cancer patients and 309 controls without cancer.
The results were encouraging:
- Higher dietary intake of omega-3s was associated with lower breast cancer risk.
- Higher blood levels of omega-3s were associated with lower breast cancer risk.
Interestingly, higher intake and blood levels of saturated fats were associated with higher risk of breast cancer.
The researchers penned this conclusion: “we showed that erythrocyte [blood cell] compositions of specific fatty acids [omega-3s] derived from fish intake… are associated with lower risk of breast cancer”
But, as they also noted, “…further studies are needed to investigate mechanisms linked to the etiology.” In other words, results from studies like this do not prove a cause-effect relationship between higher omega-3 intake and reduced cancer risk.
French findings blame omega-3/omega-6 imbalance for risk to breasts
In 2002, researchers at France's equivalent of our NIH conducted a case-control study not unlike the Japanese investigation described above, but with some important distinctions (Maillard V et al 2002).
Like the Japanese team, they set the scene by acknowledging previous evidence indicating the potential preventive effects of omega-3s: “Experimental studies have indicated that n-3 [omega-3] fatty acids... inhibit mammary tumor growth and metastasis.”
They examined adipose (fatty) tissue taken from 241 breast cancer patients with invasive, non-metastatic breast carcinoma, and from 88 patients with benign breast disease, as an indicator of the women's past dietary intake of fatty acids.
The French team found higher levels of omega-3s in breast adipose tissue correlated with reduced risk of breast cancer.
Women in the highest levels of omega-3 content were 60 percent less likely to have breast cancer, compared to women with the lowest levels.
Similarly, women with the highest levels of omega-3 DHA were 69 percent less likely to have breast cancer, compared with women with the lowest levels.
And the omega-3/omega-6 ratio was also linked strongly to cancer risk.
Women with the highest ratio of omega-3s to omega-6s were 67 percent less likely to have breast cancer, compared with women with the lowest omega-3/omega-6 ratio.
As they wrote, “In conclusion, our data… suggest a protective effect of n-3 [omega-3] fatty acids on breast cancer risk and support the hypothesis that the balance between n-3 [omega-3] and n-6 [omega-6] fatty acids plays a role in breast cancer” (Maillard V et al 2002).
Most dietary omega-6 fatty acids come from common vegetable oils—corn, soy, canola, sunflower, safflower, and cottonseed—which predominate in home cooking and in packaged and restaurant foods.
This is why researchers recommend using oils low in omega-6s, such as olive oil, macadamia nut oil, and “hi-oleic' versions of safflower or sunflower oil.
Americans also get lots of omega-6 fat from factory-farmed cattle, pigs, and poultry, which are fed grain-heavy diets high in omega-6s and low in omega-3s. Farmed salmon are also quite high in omega-6s, while wild salmon have much lower levels.
- Kuriki K, Hirose K, Wakai K, Matsuo K, Ito H, Suzuki T, Hiraki A, Saito T, Iwata H, Tatematsu M, Tajima K. Breast cancer risk and erythrocyte compositions of n-3 highly unsaturated fatty acids in Japanese. Int J Cancer. 2007 Jul 15;121(2):377-85.
- Maillard V, Bougnoux P, Ferrari P, Jourdan ML, Pinault M, Lavillonniere F, Body G, Le Floch O, Chajes V. N-3 and N-6 fatty acids in breast adipose tissue and relative risk of breast cancer in a case-control study in Tours, France. Int J Cancer. 2002 Mar 1;98(1):78-83.