By Daniel J. DeNoon
WebMD Health News
Reviewed by Laura J. Martin, MD
Nov. 2, 2010 -- The fish oil supplement DHA doesn't slow the relentless progression of Alzheimer's disease -- even if started in the earliest stages of the illness.
The disappointing finding comes from an 18-month, placebo-controlled clinical trial that enrolled 402 people with mild-to-moderate Alzheimer's disease at 51 clinical centers.
"Unfortunately, in all clinical measures we failed to see a clinical benefit of DHA supplementation," reported Joseph F. Quinn, MD, of the Oregon Health and Science University and Portland VA Medical Center at a news conference.
People who eat lots of fish have a significantly lower risk of Alzheimer's disease -- and significantly lower levels of amyloid, the chief component of the plaque that clogs patients' brains.
This benefit is thought to come from the omega-3 fatty acids in fish. DHA (docosahexaenoic acid) is one of the two major fatty acids in fish oil, and is the most abundant fatty acid in the human brain. The other omega-3 fatty acid in fish, EPA (eicosapentaenoic acid), is not found in the brain.
Quinn and colleagues reasoned that DHA supplements might slow Alzheimer's disease. But even if they looked only at the subset of patients in the very earliest stages of the illness, the treatment had no effect.
Alzheimer's Protection With Earlier DHA?
Blood tests showed that treatment with 2 grams per day of an alga-derived DHA supplement significantly increased patients' blood and spinal-fluid levels of DHA compared to patients taking placebo pills. So the negative finding wasn't due to treated patients not taking their DHA, or to patients on placebo taking DHA on the side.
"Maybe the study just started treatment too late," Quinn said. "Researchers are becoming more aware that the events that increase amyloid in the brain occur long before clinical disease. … These events are almost complete by the time a person is diagnosed with Alzheimer's disease."
Quinn tells WebMD that studies linking fish consumption to lower Alzheimer's risk look at lifelong fish consumption -- not a fish-heavy diet begun only after Alzheimer's symptoms appear.
The study "didn't answer the question of whether DHA -- taken over long periods of time and several years prior to disease onset -- could have helped prevent participants from developing the disease," Duffy MacKay, ND, vice president for scientific and regulatory affairs for the Council for Responsible Nutrition (CRN), said in a news release. CRN is a lobbying group that represents the supplement industry; Duffy was not involved in the Quinn study.
Quinn noted that studies to examine the long-term effects of DHA supplements would be costly and time consuming. A study to look at DHA use during the prediagnosis stage of Alzheimer's would need to follow 700 patients for three years. A study evaluating DHA use in people whose family history puts them at higher risk of Alzheimer's would require 4,000 participants and take five years.
The Quinn study appears in the Nov. 3 special issue of The Journal of the American Medical Association dedicated to issues regarding aging. Quinn spoke at a teleconference arranged by the journal.
Quinn is listed as a patent holder for the form of DHA used in the study, although he says he did not ask to be named in the patent and that he has waived all potential royalties from the patent.
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