The researchers in China analyzed the results of 26 international studies involving almost 900,000 women, including 20,000 who had breast cancer. The scientists found that those women who had the consumed the highest levels of omega-3 fatty acids from fish were 14 percent less likely to have breast cancer, compared with those who ate the least.
The results also showed what researchers call a dose-response relationship: each 0.1-gram increase in omega-3 per day was linked with a 5 percent lower risk of having breast cancer. For comparison, a serving of an oily fish such as salmon contains about 4 grams of omega-3 fatty acids. Oily fish are those that have high concentrations of omega-3.
Consuming the type of omega-3 found in plants, however, did not appear to reduce the risk.
Omega-3 fatty acids, a type of polyunsaturated fat, have been touted for years for their potential benefits in preventing heart disease and cancer. But not all studies have been able to confirm these claims.
Researchers who conducted a large review of 48 studiesin 2009 concluded that it was not clear whether consuming omega-3 fats, in either the diet or by taking supplements, changed a person’s risk of heart problems or cancer. However, those reviewers also said that there wasn’t enough evidence to recommend that people should stop eating foods that are rich sources of omega-3.
Other studies have suggested that it’s not just the amount of omega-3 that one consumes that matters –the ratio of omega-3s to other fatty acids in foods is important, too. In a 2002 review study, researchers found that women who consumed a balanced ratio of omega-3s to omega-6s (an unhealthy type of fat) were less likely to develop breast cancer.
In the new analysis, researchers looked at studies that measured omega-3 intake in two different ways; either by measuring omega-3 levels with blood tests, or by assessing how much fish people ate.
As soon as looking only at studies of which assessed fish diet, the researchers found there seemed to be not a significant relationship in between eating fish and reduced risk of breast cancer. However, with Asian populations, fish intake did are generally linked to a lower teat cancer risk, compared with American populations.
The researchers said maybe fish intake in Western populations is usually too low to detect any protective effect against breast melanoma.
Other factors may have motivated the findings, too, including differences between sources of omega-3, the researchers said. It’s not clear whether eating fish and taking omega-3 supplements have identical benefits.
It is possible too, that other compounds found in fish, such as pesticides and heavy metals from environmental pollution, may reduce the protective effects of omega-3, they said.