Aug. 11 (HealthDay News) -- Eating a Mediterranean diet, which emphasizes fruits, vegetables, legumes and healthy fats, and increasing physical activity levels can reduce the risk of developing Alzheimer's disease, a new study shows.

The latest research, published in the Aug. 12 issue of the Journal of the American Medical Association, is more evidence that healthy living can help ward off cognitive decline.

Following both healthy habits is a plus, said study author Dr. Nikolaos Scarmeas, an assistant professor of neurology at Columbia University Medical Center in New York City. "There is some evidence [already] that a healthy diet, the Mediterranean diet, may be protective for our risk of getting Alzheimer's disease," he said. "In the current study we wanted to see if there was an independent effect of physical activity and diet."

So Scarmeas and his team looked at 1,880 men and women without dementia living in New York, average age 77, and gave them tests every 1.5 years from 1992 through 2006, evaluating how well they followed a Mediterranean-type diet and their weekly participation in various physical activities. Those in the highest group got a median of 1.3 hours of vigorous activity or 2.4 hours of moderate-intensity exercise every week.

Scarmeas' team followed the elders for an average of 5.4 years, finding that 282 developed Alzheimer's disease during that time.

"There was an association between both a healthy diet and physical activity and reducing risk for Alzheimer's disease," Scarmeas said.

Those who ate well and exercised had a 60 percent reduction in the risk of developing Alzheimer's disease compared with those who didn't follow either good health habit, he said. "It's a very significant reduction," he added.

Exactly which components of the Mediterranean diet seem to confer benefit isn't known. "It could be there are individual elements of the diet that are important," Scarmeas said. "But it could be the interaction."

In another study published earlier this year, Scarmeas found that those who adhere to a Mediterranean diet had a lower risk of developing cognitive impairment, and a lower risk of developing Alzheimer's disease if they already had cognitive impairment.

In a second study in the same journal, researchers (including Scarmeas) looked at 1,410 French adults and found adherence to a Mediterranean diet was linked to slower decline on one cognitive test but not others. They didn't find high adherence to the heart-healthy diet linked with the risk for dementia.

In an editorial, the Mayo Clinic's Dr. David Knopman writes that a healthy diet may help prevent Alzheimer's but does not seem to occur in isolation.

"For such a benign intervention as diet and exercise, 60 percent [reduction in Alzheimer's] is substantial," said Dr. Greg Cole, associate director of the Mary S. Easton Center for Alzheimer's Disease Research at the University of California Los Angeles David Geffen School of Medicine.

Already, about 5.3 million Americans have Alzheimer's disease, according to the Alzheimer's Association, and up to 16 million may have it by 2050.

"So, the 60 percent reduction from diet and exercise can have a huge impact because we are talking about so many millions of people," Cole said.

The findings are in line with what the Alzheimer's Association already recommends in its "Maintain Your Brain" program, said William H. Thies, vice president for medical and scientific relations for the organization.

"One of the things that is important [to note] is, they are looking at normal people," he said, not those who already have the disease. "You aren't going to cure Alzheimer's disease by eating lots of olives."

SOURCES: William H. Thies, Ph.D., vice president, medical and scientific relations, Alzheimer's Association; Greg Cole, Ph.D., associate director, Mary S. Easton Center for Alzheimer's Disease Research, and professor, medicine and neurology, University of California, Los Angeles, David Geffen School of Medicine; Nikolaos Scarmeas, M.D., assistant professor, neurology, Columbia University Medical Center, New York City; Aug. 12, 2009, Journal of the American Medical Association