Diets high in the omega-3 fatty acids found in fish such as mackerel, sardines and salmon might ward off Alzheimer's disease.

That's what researchers report in the March 23 online issue of the Journal of Neuroscience.

The study was conducted in mice, but senior author Greg M. Cole said it probably applies to humans as well.

"Our data show it works in animals," said Cole, associate director of the Alzheimer's Disease Research Center at the UCLA David Geffen School of Medicine. "If this works in people, it's clearly going to be one of the ways we protect ourselves from Alzheimer's disease."

An estimated 4.5 million Americans have Alzheimer's disease, according to the Alzheimer's Association. The disease gradually destroys a person's memory and ability to communicate.

Cole's team studied older mice genetically engineered to develop Alzheimer's disease. They fed one group food fortified with docosahexenoic acid (DHA), the omega-3 fatty acid found in several types of coldwater fish. They fed the other group a diet low in DHA.

Diets low in DHA have been linked to impaired mental functioning, and DHA levels are lower in the blood and brains of Alzheimer's disease patients, Cole said.

After three to five months, which translates to several years in humans, the group of mice fed the DHA-rich diet had 70 percent less buildup of amyloid protein in the brain. This sticky protein is what makes up the plaques in the brain that are the hallmark of Alzheimer's.

"The protein is markedly reduced even when we start the diet late in life," Cole said.

"To come in and intervene late, and see a 50 percent or more reduction [in plaque] is remarkable," he added.

While the worth of omega-3 fatty acids to prevent plaque buildup in humans is yet to be proven, Cole pointed out that omega-3 fatty acids are known to have protective effects on human hearts.

The American Heart Association recommends that healthy adults eat a minimum of two servings of fish a week, especially mackerel, sardines, albacore tuna, salmon, lake trout and herring.

Another Alzheimer's expert praised the study.

"I think it's a very interesting study from a quality lab that has a history of doing work similar to this," said William Thies, vice president of medical and scientific affairs for the Alzheimer's Association. "This is looking at a mechanism that is particularly important in Alzheimer's, the accumulation of amyloid."

"There clearly is less of an accumulation of amyloid in these mice given a DHA-enriched diet," he said. "Exactly why is not quite clear."

This study, he added, "fits nicely with the idea that those things good for your blood vessels are also good for Alzheimer's disease prevention."

Based on the study results, Cole said, it makes sense to increase intake of omega-3 fatty acids. He pointed out that eggs are now supplemented with DHA, and it is also available in fish oil capsules.

In another study by Cole's group, published last year in the journal Neuron, the researchers showed that DHA protected against damage to the "synaptic" areas where brain cells communicate and enabled mice to perform better on memory tests.

The findings suggest that people genetically predisposed to getting Alzheimer's disease may be able to delay its onset by increasing their DHA intake, Cole said.

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