Omega-3 fat docosahexaenoic acid (DHA) dietary supplements, commonly sold as fish oil capsules, do not slow the progression of Alzheimer's disease, according to a study published Tuesday in the Journal of the American Medical Association.
Alzheimer's disease is a progressive, incurable and fatal brain disease affecting some 5.3 million Americans. The degenerative condition destroys brain cells, causing memory loss and problems affecting all aspects of life. Earlier observational studies suggested that a fish-rich diet might help lower the risk of developing Alzheimer's. Animal studies of the substance also showed that it might reduce some of the pathological brain changes.
The researchers hoped to validate these findings, but instead found no evidence that DHA supplements provided any benefit. The study's results mirror those of another trial published two weeks ago regarding DHA intake in pregnant women to reduce postpartum depression and improve offspring development: It, too, showed no effect.
"We have a very solid but a very negative result," said Dr. Joseph Quinn of Oregon Health and Science University, who led the study. The 18-month randomized trial among 402 mild-to-moderate Alzheimer's patients found that patients taking DHA experienced the same rates of cognitive and functional decline as those on a placebo, reported Quinn and colleagues.
There was also no difference in the rate of change of dementia, and MRI tests showed no difference between the groups on decline in total brain volume.
A Hint of Hope for a Specific Group
There was, however, a difference in the results for patients with a certain gene mutation, negative apolipoprotein E, which has been linked to dramatically increased risk for late-onset Alzheimer's disease. Such patients did exhibit smaller declines in cognitive abilities when taking the supplement as compared to those taking placebo. The authors said, however, that this finding needs to be confirmed.
Despite finding that even patients with less advanced Alzheimer's disease failed to benefit from the supplements, the authors still think that in these patients "it remains possible that an intervention with DHA might be more effective if initiated earlier." Further studies on this, however, are needed, they said. It's also possible, but unproven, that taking supplements long before symptoms appear might slow progression of the disease.
In an editorial accompanying the JAMA article, Dr. Kristine Yaffe wrote that she is disappointed that despite "two decades of neuroscientific advances in the underpinnings of AD and other forms of dementia," this study and and a similar report sponsored by the National Institutes of Health on the prevention of Alzheimer's disease are disappointing. The number of those affected by Alzheimer's and dementia is expected to increase dramatically over the coming decades as the older population grows: Such conditions already cost more than $148 billion in the U.S. annually and exact a significant toll -- financial, physical and mental -- from caregivers, and the costs associated with dementia and Alzheimer's are only set to soar.
"Therefore, there is an even greater imperative to improve" research and public policy, Yaffe wrote. With November set as Alzheimer's Awareness month, many would agree.