Epidemiologic research has indicated that diets high in omega-3 long-chain polyunsaturated fatty acids (LCPUFAs) may lower the risk of cognitive decline and dementia. But a new clinical trial—one of the largest and longest of its kind—backs up the evidence of other randomized clinical trials: omega-3 supplements do not slow cognitive decline in older adults. The study was published in the August 25, 2015 issue of JAMA.
“Contrary to popular belief, we didn’t see any benefit of omega-3 supplements for stopping cognitive decline,” said Emily Chew, MD, deputy director of the Division of Epidemiology and Clinical Applications and deputy clinical director at the National Eye Institute (NEI), in Bethesda, MD.
Dr. Chew leads the Age-Related Eye Disease Study (AREDS), which was designed to investigate a combination of nutritional supplements for slowing age-related macular degeneration (AMD). A later study, called AREDS2, tested the addition of omega-3 fatty acids to the AREDS formula.
In AREDS2, which followed 4,000 patients (average age 73, 58% female) over a 5-year period, participants who were at risk for developing late AMD were randomly assigned to 1 of 4 treatment groups:
All participants were also given a combination of vitamins C, E, beta carotene, and zinc. In addition to annual eye examinations, several validated cognitive function tests were administered at baseline and every 2 years during the 5-year study.
The researchers found that cognition scores of each subgroup decreased to a similar extent over time, indicating that no combination of nutritional supplements made a difference.
Regarding the lack of effect of the supplements, the authors speculate that the supplements were started too late in the aging process and that supplementation duration of 5 years may be insufficient. “The process of cognitive decline may occur over decades, thus a short-term supplementation given too late in the disease may not be effective,” they wrote.
They add that the observational data regarding dietary intake of specific nutrients such as omega-3 LCPUFAs and antioxidants suggest strong inverse associations with dementia, yet this trial and other randomized clinical trials have failed to show beneficial effects. “It is possible that eating foods rather than taking any specific single supplement may have an effect,” they noted.
“The AREDS2 data add to our efforts to understand the relationship between dietary components and Alzheimer’s disease and cognitive decline,” said Lenore Launer, PhD, senior investigator in the Laboratory of Epidemiology and Population Science at the National Institute on Aging, in Bethesda, MD. “It may be, for example, that the timing of nutrients, or consuming them in a certain dietary pattern, has an impact. More research would be needed to see if dietary patterns or taking the supplements earlier in the development of diseases like Alzheimer’s would make a difference.”