SUNDAY, July 12 (HealthDay News) -- Two trials that looked at whether the omega-3 fatty acid DHA might treat or prevent Alzheimer's disease have produced mixed results. The studies were done because of "a long history of epidemiological studies that related fish consumption to cognitive function," explained Bill Thies, chief medical and scientific officer of the Alzheimer's Association. Fish is rich in DHA, but the research scheduled to be presented Sunday at the association's annual meeting in Vienna, Austria, used DHA derived from algae.
An 18-month study of people with mild to moderate Alzheimer's disease "did not show treatment benefit in the study population as a whole, and does not support use of DHA for treatment of Alzheimer's disease," said study author Dr. Joseph Quinn, an associate professor of neurology at Oregon Health and Science University.
However, Quinn added that there was "an encouraging analysis of a subpopulation of the larger study," showing a slower rate of decline in mental function among those who did not have the e4 version of the APOE gene. That version is known to increase the risk of developing Alzheimer's disease. Between 70 percent and 80 percent of people have that gene version, Quinn estimated.
Still, "we're not prepared to conclude that e4-negative people should be on DHA," Quinn said. "We don't know a mechanism that would account for a benefit in e4-negative people and we don't know if our exploratory analysis would be confirmed in future trials."
His study, funded by the U.S. National Institute on Aging, included 402 people, average age 76, with a daily dietary intake of less than 200 milligrams a day. Some took 2,000-milligram DHA supplements while others took a placebo. All underwent standard tests of mental function over the 18-month trial. The slower rate of decline seen in e4-deficient participants did not reach statistical significance.
The second study was a six-month trial of 900 milligrams a day of DHA in 485 people, average age 70, who did not have Alzheimer's disease but had mild complaints about memory loss. Those taking the supplement made fewer errors on one memory test.
That trial was funded by the Martek Biosciences Corp., which markets the DHA used in both studies.
The results indicate that DHA supplements are appropriate for "people who have very mild memory complaints, which applies to a large percentage of the population at this age," said Karin Yurko-Mauro, associate director of clinical research at Martek Biosciences. "We're not talking about a disease stage here."
The company is "looking at the potential for more trials," but is still evaluating data from the completed study, Yurko-Mauro said.
"The results are certainly interesting," Thies said. "There was some improvement in memory. Then you can get into a debate about what the real-world benefit would be of that improvement in memory."
What is needed, Thies said, is a major trial for people with no Alzheimer's disease but some memory problems. "DHA is a great candidate for such a trial because it is a food supplement that is currently available," he said.
Meanwhile, Thies said, "it is too early" to make a recommendation about use of DHA supplements to prevent loss of mental function. "You would want to see more information in normal people before you make a recommendation," Thies said. "In high doses, DHA does have side effects, so you would want to see a benefit to justify the risk you are taking. We need more work for that."
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