A new review of studies that lasted up to 3.5 years suggests taking omega-3 fish oil supplements probably does not help older people ward off cognitive decline, the loss in memory and thinking skills that is a hallmark of dementia.
The London School of Hygiene & Tropical Medicine (LSHTM) researchers found participants who took the supplements performed no better in tests of mental ability than counterparts who took placebos or dummy pills.
Writing about their findings in the June issue of the Cochrane Database of Systematic Reviews, they conclude that while omega-3 fish oil supplements offered no benefits over placebo capsules or margarines in the studies they examined, longer term studies, during which greater changes in cognitive function may occur, could potentially show different results.
Dementia is a progressive illness with a cluster of symptoms associated with a reduction in brain abilities like memory, thinking, language, judgement and understanding. It typically affects people over 65 years of age.
Omega-3 long-chain polyunsaturated fatty acids (omega-3 PUFAs) are essential for healthy brain development and food sources rich in these include nuts and seeds, and oily fish such as salmon, mackerel, herring and sardines.
Previous research involving observational studies (that follow people over a period of time but do not compare similar groups under different conditions like a clinical trial does), have suggested that increasing intake of fish oils rich in omega-3 PUFAs may lead to a reduction in dementia risk, but other studies have not shown this.
In this review the researchers analyzed data on over 3,500 participants taking part in 3 randomized controlled trials. All participants were over 60 years old and none had symptoms of cognitive decline when they enrolled on the trials.
In two of the trials the participants took gel capsules for 6 or 24 months. The capsules contained either omega-3 PUFAs, or placebo in the form of olive oil or sunflower oil.
In the third study, the participants were given tubs of margarine spread for 40 months. Some received regular margarine while others received margarine fortified with omega-3 PUFAs.
In two studies covering over 3,200 participants, the omega-3 group performed no better in "mini-mental state exams" at final follow-up than the placebo group.
In two studies covering just over 1,000 participants, other mental tests like word learning, digit span and verbal fluency showed no benefit from omega-3 supplements.
However, co-author Alan Dangour, a a nutritionist at LSHTM said "these were relatively short-term studies, so we saw very little deterioration in cognitive function in either the intervention groups or the control groups. It may take much longer to see any effect of these supplements."
None of the studies examined the effect of omega-3 PUFAs on new dementia cases over the study period, which was something the researchers were particularly interested in.
Overall, fewer than 15% of participants reported side effects, and when they did they were minor, with the control groups just as likely to report them as the omega-3 groups.
The main reported side-effect of taking omega-3 PUFA supplements was mild gastrointestinal problems.
The researchers note that there was a high rate of adherence to the regime on all three trials, with an average of 90% of the supplements apparently being consumed by the participants.
The trials included in the review were well-designed and robust, so the findings are unlikely to be due to chance or bias, said an editorial note in the journal.
The researchers pointed out that although the available data appears to show omega-3 PUFA supplements do not help older people ward off cognitive decline, they may have other health benefits, and that eating fish is recommended as part of a healthy diet.