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Could fish oil help treat cognitive impairment?

Nutrition guidelines suggest that a diet rich in omega-3 fatty acids, as found in salmon, flaxseed and nut oils, helps maintain a healthy brain and heart. Supplements are popular for people who do not eat fish or other omega-3 fatty acid-rich foods. Although research indicates that these polyunsaturated fatty acids play a crucial role in brain function, findings from clinical trials of supplements have been inconsistent.

Dr. Nathan Herrmann, Dr. Krista Lanctôt and PhD student Graham Mazereeuw

Dr. Nathan Herrmann (left), Dr. Krista Lanctôt and PhD student Graham Mazereeuw are studying the effects of omega-3 fatty acid supplements on brain health.

Photo: Doug Nicholson

Seeking to understand better the effects of omega-3 fatty acids on cognitive performance, researchers in the Brain Sciences Research Program at Sunnybrook Research Institute (SRI) conducted a meta-analysis—a method that compiles and analyzes findings from many clinical trials—to assess the evidence.

Graham Mazereeuw, a PhD student supervised by scientist Dr. Krista Lanctôt and clinician-scientist Dr. Nathan Herrmann, who co-direct the neuropsychopharmacology research group at SRI, led the study. After sifting through the literature, they examined the neuropsychological benefits of omega-3 fatty acid treatment in 10 randomized controlled trials of elderly patients.

“We looked at three groups: normal controls; mild cognitive impairment, that pre-Alzheimer’s stage; and Alzheimer’s disease. Interestingly, this study showed that the positive [effect] was in the mild cognitive impairment group. That’s a very important group from a prevention point of view, because we know that a good proportion of them—about 12% to 15% per year—convert to Alzheimer’s disease,” says Lanctôt, who is also a professor at the University of Toronto.

Omega-3 fatty acid treatment was associated with a small but significant benefit in immediate recall and attention, and processing speed in patients with mild cognitive impairment, but not in healthy patients or those with Alzheimer’s disease.

“If there’s anything we can do in that middle at-risk group, it’s very important, especially if it’s going to have low side effects. Right now there are no treatments for mild cognitive impairment,” says Lanctôt.

On how omega-3 fatty acids work, Mazereeuw cites research suggesting they reduce inflammation. “It is thought that they work by having an overall anti-inflammatory and antioxidant effect, potentially reducing neuroinflammation, not only in the body, but also in the brain,” he says.

The group is now leading a randomized controlled trial investigating if treating depression in patients with heart disease with omega-3 fatty acids will improve symptoms and quality of life.

The trial is built in part on the back of their previous research. In 2010, Herrmann and Lanctôt published the second-highest cited paper since 2009 in Biological Psychiatry: a meta-analysis looking at the role of inflammatory markers in depression.

“One of the consistent findings was that two inflammatory measures, cytokines IL-6 and tumour necrosis factor alpha, had elevations in them that appeared to be consistently associated with depression,” says Herrmann, who is also a professor at U of T.

This underscores the importance of picking which patients are most likely to gain from omega-3 treatment. Mazereeuw says they are looking at blood lipid biomarkers that interact with the inflammatory system and may be related to omega-3 fatty acids. The idea is to predict which groups of patients will respond.

“If there’s a consistent signal there, with one or two different biomarkers, then we might be able to anticipate who is most likely to benefit,” says Mazereeuw.

“It matters because if there was to be an effect with the omega-3 fatty supplements, then it’s something that you can take with a high degree of tolerability and low side effects, and it’s a good preventative step that you can take from early life,” he adds.

This research was funded by the Canadian Institutes of Health Research and the Ontario Mental Health Foundation.

Dr. Nathan Herrmann, Dr. Krista Lanctôt and PhD student Graham Mazereeuw