November 3/London/Daily Mail -- Fish oil capsules do not slow mental or physical decline in Alzheimer's patients, say researchers.

The "memory-boosting" supplements did not affect progression of the disease at any stage, a £7million study found.

The increased belief in fish oil's powers of protection against degenerative brain disease has spawned a multi-million-pound industry, but the U.S. study's lead researcher Dr. Joseph Quinn, of Oregon Health and Science University, said, "We had high hopes that we'd see some efficacy, but we did not."

Fish oil supplements, rich in the omega-3 fatty acids DHA and EPA, are known to benefit brain function and some previous trials had suggested they could slow or prevent mental decline in Alzheimer's.

In the latest study, almost 400 men and women with an average age of 76 and mild to moderate Alzheimer's were randomly assigned to take either 200mg DHA pills or dummy pills daily for 18 months.

DHA occurs naturally in the brain but is found in reduced amounts in people with Alzheimer's disease.

The trial found similar rates of physical and mental decline in both groups using scoring systems and MRI brain scans. Supplements did not slow the development of Alzheimer's even in a subgroup of patients with the mildest symptoms.

"There is no basis for recommending DHA supplementation for patients with Alzheimer's disease," says a report in the Journal of the American Medical Association.

Supporters of fish oil's benefits pointed out that the latest study did not investigate whether supplements could ward off the onset of Alzheimer's in the first place.

Experts said attempting to reverse the disease after symptoms appear may be too late, as the underlying process that causes Alzheimer's begins years, if not decades, before diagnosis.

Dr. Kristine Yaffe, a dementia researcher at University of California at San Francisco, said that previous trials had shown omega-3 supplements were "associated with reduced risk of developing Alzheimer's disease" but trials on their use in those who already had the disease failed to show any impact.

Laurie Ryan, programme director of Alzheimer's studies at the U.S. National Institute on Aging, said the results were discouraging, but independent dietitian Dr. Carrie Ruxton from the Health Supplements Information Service said a recent study found high-dose supplements of DHA improved memory and learning in 485 older adults with age-related cognitive decline.

She said, "Looking at the broader range of clinical trial evidence it appears that DHA could have a beneficial effect on cognitive function in people with milder Alzheimer's disease or earlier cognitive decline.

"In the current study, DHA may have been given too late in the disease process to produce benefit.

"It is also important to note that the authors themselves concluded that an intervention with DHA might be more effective if initiated earlier in the course of the disease in patients who do not have overt dementia."

Omega-3 fatty acids in fish or supplements have been shown to help protect against heart disease and are being studied for possible effects on a range of other illnesses, including cancer and depression.

Professor Clive Ballard, director of research at the Alzheimer's Society, said, "This research contributes to the growing body of evidence showing that the omega-3 fatty acid DHA is not effective in treating people with Alzheimer's disease.

"However, we do know that a diet that includes food rich in DHA, such as oily fish and nuts, as well as plenty of fruits and vegetables, can help to reduce the risk of dementia."

From the November 15, 2010, Prepared Foods E-dition