Improvements to diet, and a reduction in diabetes, would make susceptible less vulnerable to dementia.

Experts examined 1,433 elderly people in the South of France. They were studied for signs of dementia over 7 years.

The researchers concluded that if everyone ate 3 portions of fruit and vegetables per day, new cases of dementia would fall by 6.5%. If diabetes were eliminated, the risk would fall by 4.9%.

Several other factors were studied. An improvement in educational standards was judged to be the factor that would have the biggest impact, potentially reducing dementia levels by 18%.

The findings were published in the British Medical Journal. Clive Ballard, director of research at the Alzheimer’s Society in the UK, said that taking measures to tackle diabetes, depression and heart disease could improve millions of lives. New Scientist quoted him as saying: "This important study builds on existing evidence that a healthy lifestyle can lower your risk of dementia even more than if we had been allowed to select our genes ourselves."

Mediterranean diet may help

Studies in US journals have previously suggested that a Mediterranean diet could help ward off diabetes. Such a diet contains anti-oxidant, which can protect the brain from damage. One study published in the Journal of Neurology, found that people who regularly ate omega-3 oils, found in some cooking oils and certain types of fish, were significantly less likely to develop dementia. People who ate fish once a week were 40% less likely to develop the illness.

Dementia is the serious loss of mental ability in a previously unimpaired person. It most commonly affects elderly people, but can occur at any time during adulthood. In England there are currently around 570,000 people with dementia. By 2015, it has been predicted that more than 1.7 million people will have dementia. This is partly due to the ageing UK population. However, it is also due to increased cholesterol and blood pressure, and a decline in people exercising.