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DHA Supplements Do Not Slow Alzheimer's Progression


doi: 10.1097/01.NT.0000360733.96148.e1
News From the International Conference on Alzheimer's Disease

VIENNA—Supplements of docosahexaenoic acid (DHA), an omega-3 fatty acid found in fish oil, do not appear to slow the progression of Alzheimer disease (AD) in people who have mild-to-moderate symptoms of the disorder, researchers from the National Institute on Aging-supported Alzheimer's Disease Cooperative Study (ADCS) reported here at the International Conference on Alzheimer's Disease in July.

In the study of 402 patients, there was no significant difference between patients randomized to DHA supplements and those randomized to placebo on any of the outcomes, including rate of change of memory worsening on the Alzheimer's Disease Assessment Scale-Cognitive (ADAS-cog) scale.

Study participants had mild-to-moderate AD, with a mean baseline score of 20.7 points on the 100-point Mini-Mental State Exam (MMSE). “They were living in the community, with relatively high quality of life, and not too much disability,” said lead researcher Joseph F. Quinn, MD, associate professor of neurology at Oregon Health and Sciences University in Portland.

Dr. Quinn said there were several reasons to believe that DHA would slow disease progression. “Most dietary DHA comes from fish, and people who eat a lot of fish have a reduced incidence of Alzheimer disease (AD). Also, DHA reduces Alzheimer-type changes in the brain in animal models of AD,” he said.

“The hypothesis was that DHA would slow the rate of disease progression, but unfortunately that wasn't the case,” said Dr. Quinn.

Participants were randomized to supplements containing 2g of DHA or placebo daily, for 18 months. Their dietary DHA intake was 200 mg per day or less.

Treatment with DHA clearly increased blood levels of DHA, he said, but memory worsened to a similar degree in both groups.

In a second study described at the meeting, DHA did seem to help improve learning and memory recall in healthier individuals with age-related cognitive decline who did not have AD.

The Memory Improvement with DHA Study (MIDAS) was a randomized, double-blind, placebo-controlled, multi-center study to determine the effects of 900mg/d DHA on improving cognitive functions in 485 healthy elderly people, mean age 70 years, with age-related cognitive decline.

People aged 55 or older with age-related memory complaints who took DHA supplements for six months had almost double the reduction in errors on a test that measured learning and memory skills, compared with those who took a placebo.

“The benefit is roughly equivalent to having the learning and memory skills of someone three years younger,” said researcher Karin Yurko-Mauro, PhD, associate director of clinical research at Martek Biosciences Corporation in Columbia, MD.

Blood levels of DHA doubled over the course of the study in people taking the supplements, and the higher a person's DHA level, the better the score on the cognitive tests, Dr. Yurko-Mauro reported.

“Compared to normative data, our results show a seven-year improvement with DHA versus a 3.6-year improvement with placebo, a significant difference,” Dr. Yurko-Mauro said at a press briefing.

She said the improvement among the patients taking placebo might result from a retesting effect. Just as seen with video games, participants improve at performing tasks and in using the computer over time, she explained.

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But the conflicting findings raise the possibility that treatments for AD have to be given “very early” to be effective, said William H. Thies, PhD, chief medical and scientific officer at the Alzheimer's Association in Chicago.

Dr. Thies noted that even in the study of people with age-related cognitive decline, DHA did not result in consistent improvements on all the tests of cognition and learning. Pending future research to confirm these findings, the Alzheimer's Association isn't ready to recommend that people take DHA supplements to fend off age-related memory loss, he said.

©2009 American Academy of Neurology