Women who consume plenty of omega-3 fatty acids may not have better thinking and memory skills as a result, according to a new study.
Some researchers have suggested that fatty acids found in fish and fish oil supplements might protect against memory loss.
But studies trying to test that theory have been "all over the place," said Dr. Jennifer G. Robinson from the University of Iowa in Iowa City, senior author of the new report.
"There's nothing really convincing, (in) one direction or the other," she said.
To address the uncertainty, she and her colleagues analyzed data collected as part of the large Women's Health Initiative trial focused on hormone replacement therapy.
For the new study, they compared women's fatty acid levels to their performance on six years' worth of thinking and memory tests.
The study included 2,157 women ages 65 to 80, and Robinson's team looked at their levels of two omega-3 fatty acids, docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). The researchers also adjusted for the effects of hormone therapy in the women who were taking it.
On seven kinds of thinking and memory tests, Robinson and her colleagues found no differences between the one-third of women with the lowest omega-3 levels and the one-third with the highest levels.
That was after also taking into account other health and lifestyle factors, like whether women smoked and how much they exercised.
The tests measured women's short-term memory for numbers and pictures and their ability to recognize shapes that are flipped or rotated, for example.
Scores on those exams did decline gradually over time, but there was no link between a woman's omega-3 levels and how far or fast her scores fell, the study team reports in Neurology.
Robinson said Women's Health Initiative participants tended to be healthy and well-educated, which may have bolstered their "cognitive reserve" and protected against memory loss - even without extra omega-3 fatty acids. It's possible, she added, that the fatty acids would make a bigger difference among less-advantaged women.
Or, it may be that researchers would have to measure fatty acids over longer periods of time to see a link with thought processing. The blood levels used here probably only reflect diet over several months, she said.
"It's just one snapshot, one point in time," Robinson said. "The feeling as we look at all these chronic diseases … is it's really what happens over your lifetime that's important in terms of diet and physical activity."
Alan Dangour, who has studied fatty acids and memory at the London School of Hygiene and Tropical Medicine, said omega-3s are important for brain development early in life. But after that, the data get a bit fuzzier.
"There is no good evidence to support the consumption of omega-3 supplements to promote or maintain cognitive health in later life," Dangour, who wasn't involved in the new research, said in an email.
"However, omega-3 fatty acids are an important part of the diet and may have other health benefits," he said.