The diet of southern France, Italy and Spain, rich in olive oil and red wine, is known to protect against heart disease and high blood pressure, but this is the first time it has been shown to prevent Alzheimer's disease.

Researchers monitored 2,258 healthy, elderly people in New York who were part of a research project into aging. Their medical and neurological history was assessed, they had standard physical and neurological tests and their cognitive function was measured every 18 months.

40 Percent Risk Reduction

After four years, 262 of the participants were diagnosed with Alzheimer's disease, more than one in ten of the total. Records of their diets during the study period showed that those who adhered most closely to the Mediterranean diet, eating lots of fruits, vegetables, pulses (peas, beans and lentils), some fish and alcohol with little dairy food and meat had the lowest risk of Alzheimer's, down by 39 to 40 percent.

Those who only partially followed the diet had a reduced risk of 15 to 20 percent, compared to those who consumed the typical American diet of burgers and ice cream.

Participants were scored on a scale from 0 to 9 for their adherence to the Mediterranean diet, and the risk of Alzheimer's fell around 10 percent for every additional point they climbed up the scale.

Nikolaos Scarmeas and colleagues from Columbia University Medical Center, whose findings are published in Annals of Neurology today, say: "We conclude that higher adherence to the Mediterranean diet is associated with a reduction in the risk of Alzheimer's disease."

There was a significant dose-response effect that remained even after correcting for age, gender, weight, smoking, education, and ethnicity, they say.

Combination of Factors

Previous studies have examined the link between cognitive decline and individual foods such as fruits, vegetables or oily fish, but the findings have been conflicting.

This is the first study to examine the effect of general dietary patterns, the authors say. The Alzheimer's Disease Society in the UK said the finding added to the growing weight of evidence that diet and lifestyle are important risk factors for the disease.

Professor Clive Ballard, research director, said: "This study supports the idea that eating a combined diet of plenty of fruit, vegetables and fish might help to prevent dementia.

"It is likely that the reason for this is a combination of factors. It is thought that fruit and vegetables can help to lower blood pressure and that the antioxidants found in them, including vitamins C and E, could prevent heart disease, lessening the risk of dementia as well as directly affecting potentially brain-damaging free radicals.

As we get older, eating a healthy diet including fresh fruit and vegetables, getting our blood pressure and cholesterol checked regularly, taking exercise and watching our weight may all turn out to be important ways of reducing our risk of developing dementia in laterlife.

"The Mediterranean diet has been recommended by nutritionists for over 20 years and is credited with many health benefits. Recent research has shown that the diet may contribute to the health of the unborn child in the womb and that it helps in cutting cholesterol levels."