Taking daily omega-3 fatty acid supplements doesn't seem to provide any protection against declines in thinking and memory skills in older adults, a new review of medical evidence suggests.
Because the brain is rich in the type of polyunsaturated fatty acids found in fish oil, researchers had figured that adding more of them to a person's diet could boost memory and prevent the changes that lead to cognitive decline and dementia.
But so-called "gold standard" trials of the supplements have been disappointing.
Looking at three such studies lasting between six months and over three years, researchers found there was no difference in changes on learning and memory tests among 4,000 people who took either omega-3 fish oil supplements or sunflower or olive oil as a comparison.
"The evidence suggests, from what is available at the moment, that taking supplements rich in omega-3 fatty acids is not going to benefit cognitive health later in life," said Alan Dangour, a nutrition researcher from the London School of Hygiene & Tropical Medicine, who worked on the new analysis.
The findings, he told Reuters Health, don't rule out a potential benefit on brain health in some people -- and it's still possible long-term use of the supplements may be helpful for preserving thinking and memory skills.
All three studies included in the analysis involved cognitively healthy people over age 60 who were randomly assigned to use supplements or margarine with fish oil or a placebo oil without omega-3 fatty acids.
None of those studies showed a comparative benefit for fish oil on measures of cognition, including word and number learning tests.
"The truth is many people are spending a lot of money on supplements without solid evidence they do something," said Dr. Nikolaos Scarmeas, a neurology and aging researcher at Columbia University Medical Center in New York.
Scarmeas, who wasn't involved in the new study, agreed it may take more than a few years for any benefit of the fatty acids to show up -- if one does exist. Or, it could be that getting extra fish oil through supplements only helps people who are low in the fatty acids to begin with, and not those who get enough through their diet.
But so far, he told Reuters Health, "there's no proof you'll get some benefit from it."
Other studies have suggested fish oil may have beneficial effects on heart health, and recommendations from groups such as the American Heart Association call for people to eat two servings of fish each week, preferably fatty fish such as salmon and tuna.
Neurologist Dr. Gregory Jicha from the University of Kentucky College of Medicine in Lexington said although the presumed benefits of fish oil on cognition aren't clear in randomized studies, people can still reasonably choose to take the supplements because they typically carry few risks.
Stomach problems were the most common side effect among people in the new analysis, and participants on the placebo supplements were just as likely to report mild side effects as those taking fish oil.
Omega-3 fatty acid supplements can be bought over the counter for a couple dollars per month.
Dangour said despite the shaky evidence on the role of fish oil, there are things older adults can do to ward off memory loss.
"Keeping cognitively active in later life and keeping physically active in later life are extremely important for the maintenance of cognitive function," he said.
"Once you retire, it's really important to keep your brain active."