Eating a produce-rich Mediterranean diet could significantly reduce the risk of Alzheimer’s disease, a US study has found.

The Med diet, which favours fruits and legumes, as well as fish, whole grains and olive oil has previously been thought to promote longer life, and resilience to heart disease and some cancers.

And a study published this month in an on-line version of the Annals of Neurology suggests the diet could cut the risk of the disease by up to 40 per cent.

After tracking the diets of 2258 elderly New Yorkers with no dementia for four years, researchers found that higher adherence to the Med diet was associated with significantly lower risk of developing Alzheimer’s.

Uptake of the diet was quantified and the study found that each increasing point on the Med diet score matched a 10 per cent drop in the risk of the disease.

The merits of the study could be undermined by the method of using food frequency questionnaires to determine food intake but the scientists claim that these would lessen the effect rather than exaggerate it.

Professor Clive Ballard, director of research for British Charity, the Alzheimer's Society, said the study was a useful addition to the growing interest in linking dietary lifestyle and the risk of Alzheimer's.

He said: “There have been a number of studies looking separately at the benefits of eating fruit, vegetables and oily fish for reducing your risk of Alzheimer's disease. 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 anti-oxidants 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.”

Alzheimer's disease is the most common form of dementia, affecting more than 13 million people worldwide, and costing some £15 billion in the UK alone.