TUESDAY, April 18, 2006 (HealthDay News) -- The heart-healthy benefits of the so-called Mediterranean diet are well known, but new research suggests the eating plan may reduce the risk of Alzheimer's disease, too.
People who carefully followed the Mediterranean diet -- heavy on fish, fruits and vegetables, monounsaturated fats such as those found in olive oil, and low on meat and dairy products -- had a 40 percent lower risk of developing Alzheimer's than those who ate the conventional American diet.
"That is a pretty significant effect," said Dr. Nikolaos Scarmeas, assistant professor of neurology at Columbia University Medical Center and leader of the study.
While a number of studies have shown that the Mediterranean diet decreases the risk of heart disease, this is the first research to show a benefit in terms of mental function, he said.
The finding appears in the April issue of the Annals of Neurology.
The study involved 2,258 New York City residents, who were divided into three groups, depending on how faithfully they followed the diet. For an average follow-up of four years, the rate of Alzheimer's disease was 20 percent lower for those in the middle third of adherence, and 40 percent lower for those who stuck closest to the plan, the report said.
Scarmeas said it's the diet as a whole, not any single element of it, that's responsible for the beneficial effect. And the fact that there is "a combination of many beneficial food items" in the diet makes it hard to determine exactly how the plan works, he added, but there's ample room for speculation.
One possibility is that the Mediterranean diet has the same beneficial effects on blood vessels in the brain as in the heart, reducing the risk of blockage, Scarmeas said. It could also be that the foods in the diet are rich in beneficial antioxidants, or that the diet lowers the incidence of harmful inflammation, he said.
"We tried to single out which of the components of the diet are driving its effect, but none of them is prominently responsible," Scarmeas said. "But, when we put them together, the effect was there."
Dr. Dimitrios Trichopoulos, professor of cancer prevention and epidemiology at the Harvard School of Public Health, who has done similar studies of the benefits of the Mediterranean diet, called the new research "intriguing."
"The authors seem to have done very good work," he said. "They used a diet score we have developed over the years. At face value, I think the study is a good one. This is speculation, but reasonable speculation. One has to do further work to duplicate the finding, but the results are intriguing."
There has been "a general idea" that the incidence of Alzheimer's disease is lower in regions where the Mediterranean diet prevails, Trichopoulos said. "The assumption has always been there, so that fits with this study," he said.
Trichopoulos agreed that the beneficial results "are not the effect of individual components but the entire diet. Small effects have a collective impact."
Trichopoulos said he follows the Mediterranean diet, which, Scarmeas noted, includes "moderate consumption of alcohol, usually in the form of wine during dinner."
The American Heart Association has more details on the Mediterranean diet.