Study Shows No Benefits of Omega-3 Fatty Acids on Cognitive Decline

A new retrospective cohort study found no association between levels of omega-3 fatty acids and age-associated cognitive decline in older women without dementia, contrary to previous research that demonstrated the potential benefits of omega-3 fatty acids on cognitive function.

Eric M. Ammann, MS, lead study author, Department of Epidemiology, College of Public Health, University of Iowa, Iowa City, explained that previous observational studies have reported a protective association of omega-3 fatty acid intake with cognitive function, “but this might not be cause-and-effect,” he noted.

He continued that individuals who consume a lot of fish or nuts or take omega-3 supplements tend to be more affluent and health conscious, less likely to smoke, more likely to exercise, and have a lower body mass index than those who do not.

Their study demonstrated a decline in cognitive function occurring 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,” he said.

He noted that their study sample was large and consisted of older, postmenopausal women. “In general, this was a very healthy group of women at low risk of stroke and dementia,” he said. “Our results are most applicable to women who fit that profile.”

Researchers focused on docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), two types of omega-3 fatty acids, in their analysis.

Ammann and colleagues examined 2157 women between the ages of 65 and 80 years who were enrolled in a clinical trial of postmenopausal hormone therapy (WHISCA [Women’s Health Initiative Study of Cognitive Aging]).

The relationship between prerandomization red blood cell DHA + EPA levels and (1) cognitive measures at baseline and (2) cognitive change over time were evaluated.

Blood tests to measure the amount of omega-3 fatty acids present in the patients’ blood were taken before the start of the study. Annual cognitive testing was performed on the patients for a median of nearly 6 years that included assessments of fine motor speed, verbal memory, visual memory, spatial ability, verbal knowledge, verbal fluency, and working memory.

After adjusting for demographic, clinical, and behavioral characteristics, no significant differences were found between women with high and low levels of DHA + EPA in their blood at the time of their first cognitive tests. Further, researchers found no significant differences between those with high and low levels of omega-3 fatty acids in the rate of cognitive change over time.

“We had initially expected to see a protective association, so we were a bit surprised,” said Ammann.

Despite the study’s findings, he noted that the debate on whether omega-3 fatty acids promote brain health continues.

“It’s reasonable to think that omega-3 fatty acids could be good for the brain, since they are a major constituent of neurons and may reduce the arterial hardening and inflammation that contribute to strokes,” said Ammann. “But the randomized trials suggest that if omega-3 fatty acids have a protective effect on cognition, it is probably small in the short-term and may require a lifetime to add up to something measureable. It is possible that long-term exposure to higher omega-3 levels may have mild cognitive benefits, but we just don’t know.”

When asked about the limitations of the study, Ammann pointed out that it was observational and not a randomized trial “so one must be cautious in drawing inferences about cause-and-effect from our study.” Further, the patients’ blood levels of omega-3 fatty acids were only measured at baseline. “People’s diets can change over time, and misclassification of exposure is an important limitation of most nutritional studies,” he said.

Ammann suggested that more randomized trials of omega-3 supplements will likely be performed to provide more definitive information on the relationship between omega-3 fatty acids and cognitive function in older adults. “In addition, longitudinal studies that track peoples’ dietary practices in middle age and in later years may provide richer data on the effects of diet on long-term health outcomes,” he said.

The complete study is published in the September 25, 2013 issue of Neurology. This study was supported by the National Heart, Lung, and Blood Institute, National Institutes of Health, and U.S. Department of Health and Human Services.  

-Meredith Edwards White

Reference

Ammann EM, Pottala JV, Harris WS, et al. Omega-3 fatty acids and domain-specific cognitive aging: secondary analyses of data from WHISCA. Neurology. 2013 Sep 25. [Epub ahead of print]