A diet high in the omega-3 fatty acid DHA helps protect the brain against the memory loss and cell damage caused by Alzheimer's disease.

Neuroscientists from the University of California have shown for the first time that a diet rich in DHA may lower the risk of developing Alzheimer's disease and may help slow progression of the disorder in its later stages.

Senior author and Professor of Neurology, Greg Cole PhD, at the David Geffen School of Medicine at UCLA explains "This is the first proof that our diets affect how our brain cells communicate with each other under the duress of Alzheimer's disease. We saw that a diet rich in DHA, or docosahexaenoic acid, dramatically reduces the impact of the Alzheimer's gene."

He added that the average person can easily add more omega 3 to the diet, in the form of fish oil capsules, high-fat fish, or eggs which have been supplemented with DHA.

The researchers focused on Alzheimer's damage to synapses – the chemical connections between brain cells that enable memory and learning.

They used mice which had been bred with genetic mutations that cause the brain lesions linked to advanced Alzheimer's disease. When they found that the mice developed the lesions, but showed minimal memory loss or synaptic brain damage, which might normally have been expected, the scientists took a closer look at the animals' diet.

They discovered that the mice lived on a nutritious diet of soy and fish – two ingredients rich in omega-3 fatty acids.

Because earlier studies had suggested that omega-3 fatty acids might prevent Alzheimer's disease, the researchers realised that the mice's diet could be helping to fight the progression of brain damage.

To check whether this was indeed happening, the scientists swapped safflower oil for the soy and fish to create an unhealthy diet depleted of omega-3 fatty acids. The mice were divided into two sets of older mice, which already showed brain lesions but showed no major loss of brain-cell activity. Both sets of mice were given safflower oil, which is not high in DHA, instead of the fish and soy diet. The second group were also given DHA supplements from algae.

After five months, the researchers compared each set of mice to a control group that consumed the same diet but did not carry the Alzheimer's genes. The results surprised them.

They found that the mice who were given diets low in DHA had high levels of synaptic damage in their brains, and they observed that these changes closely resembled those in the brains of humans with Alzheimer's disease.

Although the mice on the DHA-supplemented diet also carried the Alzheimer's genes, they still performed much better in memory testing than the mice in the first group.

Even after adjusting for all possible variables, DHA was the only factor remaining that protected the mice against the synaptic damage and memory loss that should have resulted from their Alzheimer's genes, according to Professor Cole. 

He said "We concluded that the DHA-enriched diet was holding their genetic disease at bay."

The UCLA scientists hope to use their findings in a new study which will track DHA-related biomarkers in the urine and cerebral spinal fluid of Alzheimer's patients. Finding these biomarkers earlier would enable treatment to begin earlier.

DHA is absorbed very quickly by the human brain, and is critical for proper cognitive function, eye development and mental tasks. DHA helps keep the brain membrane fluid, moves proteins and helps to convert signals from other parts of the body into action.

Inexpensive sources of DHA include coldwater fish, such as salmon, halibut, mackerel, sardines and herring. These fish consume algae, which is high in DHA.

However, these fish also absorb more mercury, dioxin, PCP and other metals and therefore a less risky strategy is to consume either fish oil or purified DHA supplements made from algae. Alternatively DHA-rich eggs laid by chickens that eat DHA-supplemented feed can be included in the diet.

This study was funded by The National Institute on Aging, National Institute of Neurological Diseases and Stroke, and Canadian Institutes of Health Research.

Source: EurekAlert September 1, 2004

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