Alzheimer’s disease is an irreversible degenerative disease affecting the brain, often causing severe memory loss (a result of damage to the hippocampus) and destroyed cognitive ability. Alzheimer’s, which typically begins around age 60, is the leading cause of dementia among the elderly.

Damage to the brain may begin as early as 20 years before any complications are detected. Alzheimer’s begins when neural tangles form in the entorhinal cortex. This causes the neurons to function less efficiently, and the neurons eventually die, causing these areas of the brain to shrink.

“We know that some part of Alzheimer’s is related to genetic changes and as time goes on we discover more and more of these changes,” explains lead author Nikos Scarmeas, M.D., and associate professor of clinical neurology at Columbia. “But it is also possible that non-genetic changes, including lifestyle and behavior, may also be affecting our brain health and our risk of developing brain diseases like Alzheimer’s.”

The study examined 1,880 multi-ethnic individuals, average age 77, from Northern Manhattan in New York City. The group was divided into two smaller groups, for which information on both physical activity and mental status was available. Participants did not show signs of dementia at the beginning of the study, and were followed from 1996 to 2006, measured every 18 months for neurological changes.

Participants were measured for physical activity level (no physical activity, light activity such as golfing, moderate activity like biking, or vigorous activity such as jogging) and how well they stuck to the diet (on a scale of 0-9). Diet scores were higher for individuals who consumed more fruits, vegetables, legumes and fish, and less meat, dairy and saturated fats.

“Often times people who exercise also follow a healthy diet and vice versa,” Scarmeas says. “We wanted to tease out which of these two behaviors may be associated with lower risk for AD, or if the combination of the two is associated with decreased risk even further.”

Individuals who had low physical activity had a 29-41% lower risk of developing Alzheimer’s disease than those who  were physically inactive, while individuals with “much” physical activity further decreased their risk by 37-50%. Strongly following a Mediterranean diet was associated with a 40% risk reduction for Alzheimr’s. Individuals with high diet adherence and high activity individuals showed a much lower absolute risk than those with low diet adherence and activity status, reduced from 21% to 9%.

According to Scarmeas, this study emphasizes the importance of a healthy lifestyle. "We need to understand and learn more about the exact biological mechanisms that may connect physical activity and diet with the biological changes of Alzheimer's disease," he says. "This study is important because it shows that people may be able to alter their risk of developing Alzheimer's by modifying their lifestyles through diet and exercise."

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