Omega-3 pills do not slow mental decline in people with Alzheimer's disease, a $10 million US study has found.
Previously promoted as a memory-boosting aid, pills containing DHA, an omega-3 fatty acid, were given to nearly 300 men and women with mild to moderate Alzheimer's disease. Researchers at the Oregon Health and Science University found no noticeable benefits, even for those with the mildest symptoms.
"We had high hopes that we'd see some efficacy but we did not," said Dr Joseph Quinn, an author of the study and research member.
The results with pills containing DHA highlight "the continued frustration over lack of effective interventions" for the memory-robbing disease, an editorial published with the study in the Journal of the American Medical Association said.
DHA occurs naturally in the brain and is found in reduced amounts in people with Alzheimer's disease.
Some smaller, less rigorous studies suggested that mental decline could be slowed or prevented by eating fish, the main dietary source for omega-3 fatty acids, or supplements like fish oil pills that contain fatty acids including DHA. The study used capsules of DHA oil derived from algae.
Omega-3 fatty acids in fish or supplements have been shown to help protect against heart disease and are being studied for possible effects on a range of other illnesses including cancer and depression.
"There is no basis for recommending DHA supplementation for patients with Alzheimer disease," the authors concluded.