New Study Sheds Doubt On Omega-3’s Protection Against Dementia

Three recent studies failed to show that omega-3 fatty acids, found in fish oil, slowed cognitive decline in elderly participants.

It seems that omega-3 is getting a bad rap lately. Adding to research that put into doubt its protective attributes against heart and Alzheimer’s disease, its beneficial effects against cognitive decline are now also being questioned.

Observational studies have suggested that an ingredient found in fish oil, the fatty acid omega-3, can slow cognitive decline and dementia as we get older. Yet these same observational studies in which researchers observe subjects and measure variables, but actually have no control over the conditions of the experiment, are far less ideal than a controlled experiment. A new review puts the omega-3 hypothesis to the test by bringing together data from three recent randomized controlled trials. The three separate studies compared the cognitive changes in participants whose diet was supplemented with omega-3 fatty acids to cognitive changes in those whose diet was supplemented with placebo. All three of the studies failed to show that omega-3 fatty acids have any beneficial effect on the cognitive function of the participants as they got older, putting into serious jeopardy the notion that fish oils can slow cognitive decline and prevent dementia.

A total of 3,536 participants included in the review, performed by the Cochrane Collaboration, were 60 years old or older. In order to be able to see any effects that omega-3 fatty acids might have on cognitive decline, all of the participants were tested prior to the study and only cognitively healthy subjects were accepted. In two of the studies, the participants were broken up into two groups: one that received gel capsules containing omega-3 fatty and another that receive pills containing a placebo such as olive or sunflower oil. Each group took the pills for six months or two years. At the end of the supplement period the cognitive function of the placebo and omega-3 fatty acid groups were assessed using tests such as word learning, digit span, which tests a person’s ability to remember a string of numbers, and verbal fluency. Both studies showed no difference in cognitive test scores between omega-3-supplemented and placebo groups up to two years out.

For the third study, participants took home either tubs of regular margarine spread or margarine that had been spiked with omega-3. Researchers then compared their cognitive abilities after 40 months. As with the other two studies, there was no difference between the high omega-3 group and placebo group.

Despite not protecting against cognitive decline, fish is part of a healthy diet. Eating healthy and exercising could reduce the risk of cognitive decline regardless.

It is important to point out that the lack of cognitive benefits for omega-3 fatty acids is not due to a failure on the part of the participants to stick with their supplement protocols. At the conclusion of the studies an average of 90 percent of the supplements had been consumed by the participants.

However, it may be too soon to give up on omega-3 fatty acids just yet. The margarine spread study had the longest time course, which was only three-and-a-half years. It is possible that, were the groups followed further, as signs of cognitive decline became more evident with age, any beneficial effects of omega-3 would become more evident. Indeed, over the three-and-a-half years, the study saw “little or no” cognitive decline in both the control group and the group with more omega-3.

As you might imagine with fish oil, minimal side effects were reported by the participants. Fewer than 15 percent of those in the omega-3 supplement groups reported mild gastrointestinal problems – but then, the same percentage of placebo participants also reported mild gastrointestinal problems.

Omega-3 fatty acids are concentrated in oily fish such as sardines, salmon, herring, and mackerel, and they have been shown to be essential for proper brain development. Deficits in infant docosahexaenoic acid (DHA) levels, the most common type of omega-3 fatty acid in the brain, has been linked to abnormal brain development and cognitive disorders such as attention-deficit/hyperactivity disorder (ADHD) and schizophrenia. So it may just be that omega-3 fatty acids, while vital during brain development, are inconsequential to its decline. In response to the current review, however, nutritionists and dietary experts were quick to remind us that fish – and omega-3 fatty acids – are part of a healthy diet, even if they don’t slow cognitive decline.

But then, given the three-and-a-half-year limit of the review’s time course, I think it’s safe to say that the jury’s still out on omega-3’s effects on cognition and dementia. I don’t know if a followup is planned for the three studies, but it seems only logical that there would be. But if you’re like me you’ll just continue enjoying your salmon and sardines. The news can only get better.

[image credits: Kodjo Workout, Food Insight Blog, and Supplement Updates]
images: Kodjo Workout, Food Insight Blog, and Supplement Updates

Peter Murray was born in Boston in 1973. He earned a PhD in neuroscience at the University of Maryland, Baltimore studying gene expression in the neocortex. Following his dissertation work he spent three years as a post-doctoral fellow at the same university studying brain mechanisms of pain and motor control. He completed a collection of short stories in 2010 and has been writing for Singula...

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