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Mediterranean diet associated with reduced risk of Alzheimer's disease

October 10, 2006

Eating a Mediterranean diet, which emphasizes fruits, vegetables and olive oil and includes little red meat, is associated with a lower risk for Alzheimer's disease, according to an article posted online today that will appear in the December 2006 print issue of Archives of Neurology, one of the JAMA/Archives journals. This association persisted even when researchers considered whether individuals had vascular diseases-diseases of the blood vessels, such as stroke, heart disease and diabetes-suggesting that the diet may work through different pathways to reduce Alzheimer's disease risk.

The Mediterranean diet consists of high amounts of fruits, vegetables, legumes, cereals and fish, mild to moderate amounts of alcohol and low amounts of red meat and dairy products, according to background information in the article. This diet has been associated with a lower risk for several diseases and risk factors, including cancer, obesity, high cholesterol, high blood pressure, problems with processing glucose that may lead to diabetes, coronary heart disease and overall death.

Nikolaos Scarmeas, M.D., and colleagues at Columbia University Medical Center, New York, studied whether the Mediterranean diet could also help prevent Alzheimer's disease-a debilitating neurodegenerative disease-in a group of 1,984 adults with an average age of 76.3. The participants, 194 of whom already had Alzheimer's disease and 1,790 of whom did not, were given complete physical and neurological examinations and a series of tests of brain function. Their diet over the previous year was analyzed and scored based on how closely it adhered to the principles of the Mediterranean diet-scores ranged from zero to nine, with higher scores indicating eating patterns that aligned closely with the Mediterranean diet. The researchers obtained information about vascular disease diagnoses from the exams, participants' or relatives' reports and medical records.

Eating a diet that closely followed the Mediterranean model was associated with a significantly lower risk for Alzheimer's disease. For each additional unit on the diet score, risk for Alzheimer's disease decreased by 19 to 24 percent. After the researchers considered other factors that could influence Alzheimer's disease risk, including age and body mass index, those who were in the top one-third of the diet scores had 68 percent lower odds of having Alzheimer's disease than those in the bottom one-third, and those in the middle-one third had 53 percent lower odds.

Growing evidence links the Mediterranean diet to a reduced risk for vascular disease and suggests that vascular risk factors may contribute to the risk for Alzheimer's disease, the authors write. "Thus, vascular variables are likely to be in the causal pathway between the Mediterranean diet and Alzheimer's disease and should be considered as possible mediators," they continue. "However, when we considered vascular risk factors in our models, the association between the Mediterranean diet and Alzheimer's disease did not change. This was the case despite our attempt to capture vascular comorbidity in the most complete possible way by simultaneously considering both a long list and alternative definitions of vascular variables."

"This could be the result of either other biological mechanisms (oxidative or inflammatory) being implicated or measurement error of the vascular variables," the authors conclude.

JAMA and Archives Journals