Despite doctors' advice that omega-3 fatty acids can prevent a decline in cognitive function, a new review of previous studies suggests that taking omega-3 supplements may not offer any brain benefits at all.
Researchers led by Emma Sydenham at the London School of Hygiene & Tropical Medicine analyzed data from three separate studies that evaluated the effects of omega-3 fatty acid supplementation on cognitive function among older people who showed no signs of dementia or other brain dysfunction.
The studies involved a total of 3,536 people and lasted between six and 40 months.
They found that subjects with normal brain function who either supplemented their diet with omega-3 fatty acids -- fats commonly found in fish and plant oils -- either in capsule form or by using supplement-containing margarine spreads, did not perform better on standardized tests than subjects who received a placebo.
"The results of the available studies show no benefit for cognitive function with [omega-3] supplementation among cognitively healthy older people," the authors wrote. But they did add that researchers need to conduct longer studies to assess whether there are preventive benefits.
But experts not involved in the research review say there is clear evidence of the ability of omega-3s to prevent cognitive decline.
Dr. Gary Small, professor of psychiatry and biobehavioral sciences at UCLA's David Geffen School of Medicine, said that the studies the Sydenham team evaluated have major flaws.
"Other studies have found that those who ingest omega-3 fatty acids are at lower risk of developing Alzheimer's disease," said Small.
A study published in February found a link between low levels of omega-3s and a more rapid aging of the brain and greater likelihood of losing memory and abstract thinking ability.
"Our brains are 60 percent fat. The vast majority of that fat is an omega-3 called DHA," Ski Chilton, director of botanical lipids and inflammatoroy disease prevention at Wake Forest University Baptist Medical Center in Winston-Salem, N.C., said in response to the February study. "If we can't make that DHA and we're not getting that DHA from our diet, we could be putting ourselves at significant risk of cognitive decline, dementia and mental illnesses such as schizophrenia and bipolar disorder and attention deficit hyperactivity disorder."
Small, also the author of "The Alzheimer's Prevention Program," stressed it's preferable for people to get omega-3s through food and not supplements, but the supplements are still beneficial and doctors are still likely to recommend them for brain and other benefits.
The extent of those cognitive benefits remains under debate, however, said Dr. Samuel Gandy, a professor of Alzheimer's disease research at Mount Sinai Medical Center, in New York.
"There is some evidence that omega-3s may protect from aging-associated memory impairment, but there is no consistent evidence that omega-3s delay or protect from Alzheimer's disease," he said.
While the role of omega-3 fatty acids in protecting the brain still needs to be fleshed out, the researchers who performed the study review stressed that omega-3s may offer other benefits. While they didn't mention it specifically, helping protect against cardiovascular disease is one of them. Eating fish, they wrote, "is recommended as part of a healthy diet."