(The New York Times News Service) -- Louisiana State University scientists say they have discovered how the fatty acids found in fish oil help protect the human brain from the type of cognitive decline associated with Alzheimer's disease.

Their study shows that docosahexaenoic acid, an omega-3 fatty acid found in coldwater fish such as mackerel, sardines and salmon, reduces levels of a protein known to cause damaging plaques in the brains of Alzheimer's patients.

What's more, the researchers discovered that a derivative of DHA, which they dubbed "neuroprotectin D1," is made in the human brain. That natural substance plays a key role, too, in protecting the brain from cell death, the study showed.

"Now what does this tell us from the point of view of the disease? I believe that, obviously, diet is a major issue here," says Dr. Nicolas G. Bazan, director of the Neuroscience Center of Excellence at the Louisiana State University Health Sciences Center in New Orleans.

"DHA is an essential building block for the structure of brain cells," he notes. "And now we are finding that this building block also makes a 'golden brick' (neuroprotectin D1) that helps the life of the neurons to continue."

Greg M. Cole, associate director of the Alzheimer's Disease Research Center at the University of California, Los Angeles David Geffen School of Medicine, says the study "provides strong evidence" that NPD1 offers "several important protective contributions."

The study was released online Sept. 8, in advance of its Oct. 1 publication in The Journal of Clinical Investigation.

Bazan, who is currently staying in Philadelphia, had been in Poland to give the opening lecture at a meeting on neurodegenerative diseases when Hurricane Katrina struck New Orleans. So far, he says, he has re-established contact with about half of the roughly 115 people who work at the LSU neuroscience center.

Due to the state of emergency in New Orleans, the center won't resume work until perhaps late November or early December, interrupting what Bazan calls the most exciting period in his scientific career.

Indeed, while previous studies have suggested that DHA reduces the risk of Alzheimer's-related cognitive deficits, scientists haven't explored how the fatty acid may work its protective magic.

Some 4.5 million Americans have Alzheimer's disease, according to the Alzheimer's Association. If no cure is found, as many as 16 million could have the disease by 2050, as the population ages.

Bazan and colleagues at LSU and Brigham & Women's Hospital in Boston conducted a series of experiments. Some of the testing involved post-mortem human brain samples harvested from six patients who had Alzheimer's disease and an equal number of age-matched "control" samples from people who did not have the disease.

The researchers also used technology called tandem mass spectrometry to analyze changes within brain cells.

Studies show DHA is highly concentrated in the brain and retina of the eye. In earlier research, Bazan's team discovered that NPD1 is produced in cells that are critical for vision. They wondered whether the brain might do the same.

"And the human brain, sure enough, makes neuroprotectin D1," Bazan found.

Cole, the UCLA researcher, notes: "This study also shows that both DHA and its NPD1 product are effective in treating human brain cells and reducing the inflammation and toxicity from a toxin called beta amyloid that is widely believed to cause Alzheimer's."

The researchers also examined specific areas of the brains of people with Alzheimer's, including an area critical to memory formation and cognition. "And that area shows huge -- I mean 20-, 25-fold -- decreases in neuroprotectin D1, as compared with other areas in the same human brain," Bazan says.

Furthermore, in cell studies designed to mimic the effects of aging, the team found that adding DHA reduced the secretion of toxic beta amyloid proteins and, at the same time, spurred production of NPD1.

"We are concluding that neuroprotectin D1 induces a gene expression program that is neuroprotective, meaning that it promotes survival of brain cells," Bazan says. And that discovery, he adds, could one day lead to the development of a new treatment to slow the progression of Alzheimer's disease.

For now, though, people should pursue a nutritional approach to warding off Alzheimer's and diminishing the effects of the disease.

Since DHA sources are safe, cheap, available and clinically proven to fight heart disease, the nation's number one killer, Cole says he would advise families of Alzheimer's patients to make sure their loved ones get the minimum recommended DHA from their diet or supplements.

Experts recommend 200 to 300 milligrams per day -- a far greater amount than the 60 to 80 milligrams daily that Americans typically get in their diet, he notes.

Copyright 2005 The New York Times News Service. All rights reserved.