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 (DHA), 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” (NPD1), 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,” said 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 noted. “And now we are finding that this building block also makes a ‘golden brick’ (NPD1) 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, said the study “provides strong evidence” that NPD1 offers “several important protective contributions.”

ndeed, 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 postmortem 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.