If there were a food or dietary supplement guaranteed to help preserve our thinking skills, memory and verbal fluency later in life, we'd all take it. Unfortunately, we don't have such a miracle pill.
Omega-3 fatty acids, found in fatty fish and nuts, have been touted as potential brain-boosters in aging. In some studies they were shown to be associated with a lower risk of dementia.
A new study in the journal Neurology is a knock against that theory, but more research needs to be done to confirm, as it does not prove or disprove a cause-and-effect relationship.
"Our study was observational and should not be viewed as a definitive answer on the relationship between omega-3s and cognitive function," lead study author Eric Ammann of the University of Iowa said in an e-mail. "In making health-related decisions about diet and supplements, we would advise people to consider the total body of evidence and to consult with their health care providers."
The study looked at 2,157 women aged 65 to 80 who had normal cognition and were already enrolled in a clinical trial for hormone therapy. They were part of a sub-study of the large Women's Health Initiative study.
Researchers followed the participants for a median of 5.9 years.
The study authors analyzed results from blood samples that were taken from participants before they were randomly assigned to take estrogen or placebo in the broader Women's Health Initiative Study.
Researchers looked at two omega-3 fatty acids, which have been implicated in protection against cardiovascular disease and cognitive decline: DHA and EPA. They measured biomarkers of these fatty acids in participants' red blood cells as a way of seeing how much exposure they had to these acids.
Participants also received a variety of tests to assess such skills as fine motor speed, spatial ability, short-term visual memory, verbal memory, verbal knowledge, verbal fluency and working memory. They took these cognitive assessments annually during the study.
Researchers did not find a significant association between the DHA + EPA levels and cognitive function at the start of the study, or with change over time in any of the areas that were tested.
"In our study, cognitive function declined at the same rate in older women across the range of omega-3 blood levels. Our results are more in line with the findings of randomized trials of omega-3 supplements, which have not found a protective effect on cognition over short treatment periods," Ammann said.
A randomized controlled trial, in which participants are randomly assigned to take a given quantity of omega-3s -- or not -- is considered much stronger scientifically than an observational study such as this one. A 2012 systematic review of such studies found no evidence that omega-3s in cognitively healthy older people leads to cognitive benefits, but noted that studies of longer duration are required for further investigation.
Why, then, have associations been found in other studies between omega-3s and brain benefits? Ammann points out that people who eat a lot of fish or nuts, or take omega-3 supplements, may be more affluent and health-conscious than those who do not. "They are also less likely to smoke, more likely to exercise, and have a lower body mass index," he said.
Although the new study had a large sample size and gave annual cognitive tests to participants, there are a few caveats that limit the strength of the study. For instance, the DHA + EPA levels were measured at the start of the study but never again, even though participants' dietary habits may have changed over time.
Furthermore, participants in this study were all women and tended to be healthier and more educated than the average older American woman who does not have dementia, the study said.
More research is necessary to see whether omega-3s really do live up to the potential hailed by other studies. In the meantime, talk to your doctor about what diet and supplements are right for you.