A large clinical trial in the US has found that omega-3 supplements will not slow cognitive decline in older people, debunking earlier research that a diet high in omega-3 fatty acids can protect brain health.
The team from the US National Institutes of Health (NIH) followed 4,000 patients over a five-year period to reach this conclusion.
"Contrary to popular belief, we did not see any benefit of omega-3 supplements for stopping cognitive decline," said Emily Chew, deputy director of the Division of Epidemiology and Clinical Applications and deputy clinical director at the National Eye Institute (NEI), part of NIH.
Omega-3 fatty acids are made by marine algae and are concentrated in fish oils.
These are believed to be responsible for the health benefits associated with regularly eating fish such as salmon and tuna.
Where studies have surveyed people on their dietary habits and health, they've found that regular consumption of fish is associated with lower rates of age-related macular degeneration (AMD), cardiovascular disease and possibly dementia.
"We have seen data that eating foods with omega-3 may have a benefit for eye, brain and heart health," Dr Chew added.
In participants, 72 year old on average and suffering from early or intermediate AMD, Dr Chew and her team investigated the possible cognitive benefits of omega-3 supplements.
The groups were given either a placebo pill, omega-3 supplements or Lutein and zeaxanthin - nutrients found in large amounts in green leafy vegetables.
The researchers found that the cognition scores of each sub-group decreased to a similar extent over time, indicating that no combination of nutritional supplements made a difference.
"It may be that the timing of nutrients or consuming them in a certain dietary pattern has an impact," said Lenore Launer, senior investigator at the National Institute on Aging.
"More research is needed to see if dietary patterns or taking the supplements earlier in the development of diseases like Alzheimer's would make a difference," Launer added.
The paper was published in the Journal of the American Medical Association