Fish oil, best known for its role in preventing heart disease, may also help reduce the risk of Alzheimer's disease.

Fish oil is an excellent source of the essential omega-3 fatty acids docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). These fatty acids are considered "essential" because the human body cannot manufacture them; they must be obtained from foods in the diet.

Thousands of studies have confirmed the heart-healthy benefits of DHA and EPA, including dramatic reductions in heart attacks, strokes and even death. In three clinical trials involving more than 30,000 participants, supplementation with DHA and EPA reduced the occurrence of adverse cardiovascular events by as much as 45 percent.

A growing body of scientific evidence suggests that the omega-3 fatty acids in fish oil, especially DHA, may offer significant protection against Alzheimer's disease. Previous studies have linked low levels of DHA in the brain to a greater risk of cognitive impairment.

Data from the Framingham Heart Study revealed that individuals with the highest blood levels of DHA had a 39 percent reduction in the risk of developing Alzheimer's compared to those with lower levels.

Prescription drugs are available to treat the symptoms of Alzheimer's, but these medications don't address the underlying cause of the disease, nor do they slow its progression. Preliminary research offers hope that DHA may be useful in the prevention and treatment of the illness.

Although the mechanisms by which DHA protects the brain are not entirely clear, scientists are making progress in understanding the beneficial effects of the essential fatty acid. Some experts believe the substance's anti-inflammatory properties may play a key role.

Researchers at the University of Michigan reported that the omega-3 fatty acids in fish oil diminish the production and inhibit the action of various prostaglandins — naturally occurring hormone-like substances that trigger inflammatory processes in the body. Inflammation is believed to contribute to the development and progression of Alzheimer's disease.

Earlier this year, researchers at University of California, Los Angeles reported that DHA from fish oil increases production of a protein found at reduced levels in Alzheimer's patients. The protein, dubbed LR11, is known to destroy components of beta amyloid plaques — structures that are toxic to neurons and contribute to Alzheimer's.

In animal studies, the researchers discovered that even at low doses, DHA increased levels of LR11 in the brains of rodents that had been genetically altered to develop Alzheimer's disease.

Scientists at the University of California, Irvine found that in addition to slowing the growth of beta amyloid plaques, DHA can interfere with the accumulation of the protein tau, which leads to the development of neurofibrillary tangles in the brain. Like beta amyloid plaques, neurofibrillary tangles are a signature lesion of Alzheimer's.

Based on these findings, it's likely that diets rich in DHA can help prevent the development of Alzheimer's later in life. Unfortunately, the typical American diet is lacking in essential fatty acids, providing between 60 milligrams to 80 milligrams a day, far lower than the recommended daily minimum of 250 milligrams.

Food sources of essential fatty acids include coldwater fatty fish, such as salmon, mackerel, herring and tuna. Two daily servings can provide 400 milligrams to 500 milligrams of DHA and EPA. For folks who aren't able to consume adequate amounts of fish, high-quality fish oil supplements are an excellent alternative source of essential omega-3 fatty acids.

Although researchers are still working to determine the optimal dose of DHA for the prevention of Alzheimer's, it's likely that the same doses used to protect the heart can also protect the brain. The American Heart Association has published guidelines for the prevention of adverse cardiovascular events.

Healthy individuals without heart disease are encouraged to eat a variety of fatty fish at least twice weekly. For patients diagnosed with coronary heart disease, the organization recommends a daily intake of 1 gram EPA plus DHA daily.

Individuals who take essential fatty acids in the form of dietary supplements are advised to do so with a physician's supervision. Fortunately, fish oil supplements are generally safe and well tolerated.

The most commonly reported complaints are mild stomach upset and a fishy aftertaste. Freezing fish-oil capsules or taking them with meals or before bedtime can reduce the likelihood of experiencing unpleasant side effects.

Boosting your daily intake of essential fatty acids may take a little extra effort, but when it comes to protecting the health of your heart and your brain, it's an excellent investment.

Rallie McAllister is a board-certified family physician, speaker and the author of several books, including "Healthy Lunchbox: The Working Mom's Guide to Keeping You and Your Kids Trim." Her website is www.rallieonhealth.com. To find out more about Rallie McAllister, M.D., and read features by other Creators Syndicate writers and cartoonists, visit the Creators Syndicate Web page at www.creators.com.

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