In a prospective cohort study of 1880 community dwelling elders without dementia  published in the August 12, 2009 issue of JAMA, the Journal of the American Medical Association, both higher adherence to a Mediterranean-style diet and higher physical activity were independently associatd with reduced risk for Alzheimer's disease (AD).
Lead by Dr. Nikolaos Scarmeas, researchers administerd standardized neurological and neuropsychological measures every 1.5 years over a fourteen year period and tracked adherence to a Mediterranean-style diet and a physical activity log.  Subjects in the highest diet adherence group was associated with a 32% to 40% reduction in risk.  Similarly, individuals reporting high levels of physical activity had a 33% to 48% lowere risk for AD.
High levels of physical activity in the study corresponded to 1.3 hours of vigorous activity per week, 2.4 hours of moderate activity or 4 hours of light activity.  Even this modest levelof physical activity was associated with a risk reduction for AD.   In a separate observational study in 2008, investigators looked at the relationship of physical activity and mental function in about 6,000 women age 65 and older, over an 8 year period. They found that the women who were more physically active were less likely to experience a decline in their mental function than inactive women.
Scarmeas and colleagues first reported a link between the Mediterranean diet and Alzheimer's risk in a study involving 2,258 New Yorkers published in June  2006 in the Annals of Neurology.  In an effort to confirm the findings, the Columbia University researchers repeated the trial in roughly 2,000 people who either had the disease or were at risk for developing it. The average age of the participants was 76, and roughly one in 10 had a diagnosis of Alzheimer's disease.  The researchers reviewed the diets of all study participants over the course of a year to determine how closely the subjects adhered to the principles of the Mediterranean diet.

Long suspected of lowering the risk of heart disease and diabetes, the Mediterranean diet consists of large amounts of fruits, vegetables, beans, grains, and nuts. Red meats are eaten only rarely and poultry, eggs, and dairy products are eaten in moderation. Olive oil and fatty fish are the main sources of fat in the diet.  Just as with their previous study, Scarmeas and colleagues found that people who most closely followed the Mediterranean model had the lowest Alzheimer's risk.  People who most closely adhered to the diet had an Alzheimer's risk that was 40 percent to 65 percent lower than people who were least likely to follow the diet.