London School of Hygiene & Tropical Medicine

The largest ever trial of fish oil supplements has found no evidence that they offer benefits for cognitive function in older people. The OPAL study investigated the effects of taking omega-3 long-chain polyunsaturated fatty acid supplements over a two year period on the cognitive function of participants aged 70-80 years.

The number of people with cognitive impairment is rising and it is estimated that by 2040, more than 81 million people globally will have dementia. Some studies have suggested that high intakes of omega-3 fatty acids, most commonly found in oily fish, are important for the maintenance of good cognitive health in later life.

The OPAL (Older People And omega-3 Long-chain polyunsaturated fatty acids) study, published today in the American Journal of Clinical Nutrition, was a randomised controlled trial led by Alan Dangour, Senior Lecturer at the London School of Hygiene & Tropical Medicine and colleagues. The study enrolled 867 participants aged 70-80 years from General Practice clinics in England and Wales. Trial participants who all had good cognitive health at the start of the study were randomly assigned into two groups, one of which received fish oil capsules while the other group received a placebo for two years. Cognitive function was assessed at the start and end of the study by trained research nurses using a series of paper and pencil tests of memory and concentration.

After two years, those participants receiving fish oil capsules had significantly higher levels of omega-3 fatty acids in their blood than those participants receiving placebo capsules. However, cognitive function did not change over the course of the study in either group of participants and there was no evidence that the consumption of omega-3 fatty acids had a benefit for cognitive function in older people.

Dr Alan Dangour urges caution in interpreting these results: “From the data we have collected in the OPAL study there is no evidence of an important benefit for memory or concentration of increased omega-3 fatty acid consumption over a two year period among older people with good cognitive health. However, it is important to keep in mind that poor cognitive function can take many years to develop and although this is the longest trial of its kind ever conducted, it may be that it was not long enough for any true beneficial effects to be detected among this healthy cohort of older people”.