A large review of studies concludes
that women who consume more omega-3 fatty acids by eating fish were at a lower
risk of having breast cancer.
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 studies in 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.
When
looking only at studies that assessed fish diet, the researchers found there
was not a significant relationship between eating fish and reduced risk of breast cancer. However, in
Asian populations, fish intake did tend to be linked to a lower breast cancer
risk, compared with Western populations.
The researchers said perhaps fish
intake in Western populations is too low to detect a protective effect against
breast cancer.
Other factors may have influenced the
findings, too, including differences between sources of omega-3, the
researchers said. It is not clear whether eating fish and taking omega-3
supplements have equal 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.
The study is published today (June
27) in the British Medical Journal.
By
BAHAR GHOLIPOUR
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