Fish Oil Offers No Benefit To Older Adults' Cognition - Two-Year Study

Consumption of omega-3 fatty acids has no measurable effect on cognition in older adults, according to U.K. researchers looking at whether daily use of the supplements could prevent cognitive decline.

In a two-year, blinded study funded by U.K. health and nutrition agencies and published in the American Journal of Clinical Nutrition, a team of investigators led by Alan Dangour, of the London School of Hygiene & Tropical Medicine, randomly assigned 867 older adults in good cognitive health and who did not take fish oil supplements to a daily dose of 200 mg eicosapentaenoic acid plus 500 mg docosahexaenoic acid, or an olive oil placebo.

Dangour's team suggested more conclusive results could be generated from future trials involving larger dosages of omega-3, with longer treatment or follow-up periods, carried out in a population with lower fish consumption, or using subjects with mild cognitive impairment.

The mean age of participants was 75 years; 55 percent were men. Though concentrations of EPA and DHA were significantly higher in blood samples from the treatment group, no decline in cognitive function was detected in either group.

"After two years we can say definitively that there's no benefit. We're disappointed, but we conducted the best possible study and certainly the largest to date," Dangour, a physician, said in an interview.

Standardized tests of memory and cognitive function and serum EPA and DHA levels were administered at baseline and after 24 months. In the treatment arm, 376 subjects completed the study, compared with 368 in the control arm. Analysis was by intention to treat.

The findings appear in stark contrast to those of a 2006 study of 899 similar-age subjects from a large cohort. In that study, people in the top quartile of plasma DHA levels saw a 47 percent reduction in the risk of developing all-cause dementia after nine years (¹ (Also see "Higher DHA Intake Associated With Reduced Risk Of Dementia – JAMA Study" - Pink Sheet, 20 Nov, 2006.)).

But cohort studies are difficult to compare with randomized, controlled trials, Dangour pointed out, and "there are loads of other studies that say there's a benefit for people who eat more fish."

The point of this study, specifically, was to detect a measurable benefit from a dietary change rather than the accumulated benefits of a lifelong habit.

Compared with other studies testing the benefits of omega-3 polyunsaturated fatty acids, the dosages used by Dangour's team were modest - the equivalent of about 250 g of oily fish per week. The reason, he said, was to test amounts that could realistically be translated into a public health recommendation, had the results proven significant.

Looking At Interventions For Elderly Health

"We consider the increase in the number of older people to be the largest challenge of public health globally," Dangour said. "So if we can identify simple, cost-effective interventions it's going to be very important. Unfortunately this wasn't one."

A limitation of this study, the researchers acknowledged, was the relative good health of the subjects. Further, many of them might have been consuming adequate levels of omega-3 polyunsaturated fatty acids already from eating fish - blood tests after 24 months did not show insufficiencies in the control group.

The study excluded patients with diabetes from participating, and only 17 subjects died during the two-year period, much lower than the 55 deaths than would be expected for a group of the same age and sex distribution in the U.K.

"People who join those studies ... tend to be healthier overall," Dangour said. "Had our sample been the same size group representative of the [overall health picture] in the U.K. for that age group then we would have likely seen more decline. In the group of individuals we were looking at the declines were slower."

Neither Dangour nor his coauthors declared any competing interests. Ocean Nutrition Canada Ltd. donated fish oil for the study.

[Editor's note: This story appears courtesy of Elsevier Global Medical News. For more information, please call 240-221-4530.]

- Jennie Smith