CHICAGO (Reuters) - Omega-3 fatty acid supplements did nothing to slow memory declines in people with mild to moderate Alzheimer's disease, but a study in healthy people with slight memory complaints did show promise, U.S. researchers said on Sunday.
The findings from an 18-month, government-backed study suggest taking supplements of docosahexenoic acid, or DHA -- an omega-3 fatty acid -- does not arrest Alzheimer's in people who have already developed the mind-robbing disease.
"These trial results do not support the routine use of DHA for patients with Alzheimer's," Dr Joseph Quinn of Oregon Health and Sciences University in Portland, who led the study, said in a statement.
But a six-month company study that looked at people whose memory was slipping just a bit found Martek Biosciences Corp's DHA supplements helped restore some of the mental acuity they had lost.
"The benefit is roughly equivalent to having the learning and memory skills of someone three years younger," Martek researcher Karin Yurko-Mauro said in a telephone interview.
Both studies, which are being presented at an international Alzheimer's Association meeting in Vienna, Austria, show the difficulty of treating Alzheimer's disease, which causes memory loss, confusion, the inability to care for oneself and eventually death. It affects 26 million people globally.
Taken together, the findings along with other studies suggest treating Alzheimer's must begin early in the disease process, before sticky amyloid plaques begin forming toxic clumps in the brain.
"It may be that ... by the time you have Alzheimer's disease, it is too late," Dr Ronald Petersen, director of Alzheimer's research at the Mayo Clinic in Rochester, Minnesota, said in a telephone interview.
Plenty of studies in both mice and people had suggested that a diet rich in DHA -- an omega-3 fatty acid found in fatty cold-water fish -- could dramatically slow Alzheimer's disease, and hopes were high for DHA as a possible new treatment.
DHA is naturally found in the body in small amounts, and is the most abundant omega-3 fatty acid in the brain.
In the Alzheimer's study supported by the National Institute on Aging, Quinn and colleagues compared Martek's DHA supplements to a placebo in 402 people with mild to moderate Alzheimer's. Although blood levels of DHA increased, the team saw no change in two widely accepted Alzheimer's tests.
But the study did suggest some benefit in people with Alzheimer's who do not have the ApoE4 gene, which raises their Alzheimer's disease risk. Quinn called the finding "intriguing" because other trials have shown different response rates based on this gene, and said future studies should look at this.
In the six-month Martek study, researchers looked at the effects of a 900 mg daily dose of DHA on 485 healthy people with an average age of 70 who had a mild memory complaint. People in this study were tested using a computer memory test.
At the end of six months, those who took DHA made far fewer mistakes than those in the placebo group. The effect was "almost double," Yurko-Mauro said.
Petersen, a former vice chairman of the Alzheimer's Association, said the study was promising, but needs to be confirmed before healthy people start taking DHA supplements.
"The association is not recommending normal elderly people take DHA based on this study," he said.
Editing by Eric Beech