A Mediterranean diet rich in vegetables and fruit and low in saturated fats could lower the risk of Alzheimer's disease, a US study has concluded.

Columbia University Medical Center researchers studied nearly 2,000 American adults with an average age of about 76.

They found that eating a diet that closely followed the Mediterranean model was linked with a significantly lower risk of Alzheimer's.

The work will be published in the December issue of Archives of Neurology, one of the JAMA/Archives journals.

The participants were each given a score (from 0 to 9) based on adherence to a Mediterranean diet, with higher scores for those who ate the most foods linked to such a diet.

For each additional point on the diet score, risk of Alzheimer's decreased by 19 to 24 per cent.

Those who were in the top one-third of the diet scores had 68 per cent lower odds of having Alzheimer's disease than those in the bottom one-third.

The researchers believe the Mediterranean diet fights against vascular disease - a condition that may increase the risk of Alzheimer's.

"Thus, vascular variables are likely to be in the causal pathway between the Mediterranean diet and Alzheimer's disease and should be considered as possible mediators," the team said in their report.

"However, when we considered vascular risk factors in our models, the association between the Mediterranean diet and Alzheimer's disease did not change.

"This was the case despite our attempt to capture vascular comorbidity in the most complete possible way by simultaneously considering both a long list and alternative definitions of vascular variables."

The Mediterranean diet is characterised by a high intake of vegetables, legumes, fruits, and cereals and a moderate to high intake of fish.

It also includes a low intake of saturated fats, but high intake of unsaturated fats, particularly olive oil, and a low intake of dairy products and red meat, and a modest consumption of alcohol, mostly as wine.

Previous research has linked the Mediterranean diet to a reduced risk of cancer, obesity, high cholesterol, high blood pressure and coronary heart disease.

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