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Eating a "Mediterranean diet" of fruits, vegetables, legumes, cereals, fish, and olive oil - which has been popular for many years in Israel but is gradually being supplanted in some sectors by American-style junk food - has been linked with a lower risk of Alzheimer's disease.
This was published on-line Monday and will appear in the December 2006 print edition of the Archives of Neurology, a publication of the Journal of the American Medical Association (JAMA) group. This connection persisted even when researchers considered whether individuals had diseases of the blood vessels, such as stroke, heart disease and diabetes, suggesting that the diet may work through different pathways to reduce the risk of this major type of dementia.
The Mediterranean diet consists of high amounts of produce, legumes, cereals and fish, mild to moderate amounts of alcohol and low amounts of red meat and fatty 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.
In a retrospective study, Dr. Nikolaos Scarmeas and colleagues at Columbia University Medical Center in New York investigated whether the Mediterranean diet could also help prevent Alzheimer's disease - the most common debilitating neurodegenerative disease in older people - 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 numbers 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 percent to 24%. 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% lower risk of having Alzheimer's disease than those in the bottom one-third, and those in the middle-one third had 53% 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.