Dietary supplementation with omega-3 fatty acids did not prevent cognitive decline in older individuals, a Cochrane review determined.

For instance, the mean difference in scores on mini-mental state examinations given before and after the intervention was a nonsignificant −0.07 (95% CI −0.25 to 0.10), according to Emma Sydenham, MSc, of the London School of Hygiene and Tropical Medicine, and colleagues.

“Global estimates suggest that by the year 2040 more than 80 million people will be affected with dementia, and more than 70% of these people will live in low-income countries,” the reviewers wrote. Accordingly, there is increasing interest in identifying dietary factors that could help diminish these numbers.

Some previous observational studies have suggested that consuming high levels of polyunsaturated fatty acids may reduce the likelihood of cognitive decline with aging. In addition, evidence exists suggesting an important role for fatty acids in brain health, such as through the maintenance of neuronal functioning and acting as mediators of inflammation and oxidative stress.

So Sydenham and colleagues undertook a literature search, identifying three trials of omega-3 fatty acid supplementation in which 3,536 participants were randomized to the intervention or placebo and had assessments of cognitive function at baseline and study conclusion.

The three studies were high in methodologic quality, the researchers noted.

One study included 302 Dutch participants ages 65 and older who received 1,940 mg or 400 mg omega-3 fatty acids, or placebo, each day for 6 months.

The second study included 744 U.K. men and women ages 70 to 79 given 700 mg omega-3 fish oil daily, or olive oil as placebo, for 24 months.

In these two studies, cognitive function was assessed by a series of tests of memory, executive function, and processing speed. Participants in the British study also completed the mini-mental status examination.

The third study randomized 2,911 participants ages 60 to 80 to use margarine fortified with 400 mg docosahexaenoic acid (DHA), 2 g of alpha linolenic acid (ALA), DHA plus AHA, or placebo for 40 months.

This study was primarily intended to assess the cardiovascular effects of the fortified margarine among patients who had previously experienced a myocardial infarction. The omega-3 sub-study evaluated cognitive functioning on the mini-mental status examination.

Overall, no differences were seen in cognitive function in the three studies.

On tests of immediate word recall involving 1,043 individuals, the standardized mean difference for the intervention was 0.01 (95% CI −0.11 to 0.14), while the difference for delayed word recall was −0.04 (95% CI −0.16 to 0.09).

For tests of verbal fluency, the standardized mean difference was 0.06 (95% CI −0.06 to 0.18), the researchers reported.

On the digit span tests of executive function, forward repeating of series of numbers was associated with a mean difference of 0.03 (95% CI −0.25 to 0.31), while backward repeating was associated with a mean difference of 0.12 (95% CI −0.12 to 0.36).

In all three studies, mild gastrointestinal symptoms were the most common side effects, and were reported with equal frequency in treatment and placebo groups.

The reviewers concluded that further studies are needed.

“Longer-term studies may identify greater change in cognitive function in study participants which may enhance the ability to detect the possible effects of omega-3 [polyunsaturated fatty acid] supplementation in preventing cognitive decline in older people,” they stated.

And while cognitive benefits were not demonstrated in this review, Sydenham and colleagues emphasized that consumption of two servings of fish each week, with one being an oily fish such as salmon or sardines, is widely recommended for overall health benefits.

Primary source: The Cochrane Collaboration
Source reference: Sydenham E, et al “Omega 3 fatty acid for the prevention of cognitive decline and dementia” Cochrane Database of Systematic Reviews 2012; DOI: 10.1002/14651858.CD005379.pub3.