Eating a "Mediterranean-style" healthy diet significantly reduces the risk of developing Alzheimer's disease, a study has suggested.
Vegetables make up a significant part of the Mediterranean diet
US researchers looked at the diet and health of 2,200 people over four years.
The more people kept to a Mediterranean diet, the less likely they were to develop Alzheimer's, according to the Annals of Neurology study.
Alzheimer's experts said the research added to evidence that a healthy diet could have a protective effect.
The Mediterranean diet - rich in fruit, vegetables and cereals with some fish and alcohol and very little dairy and meat - has been cited as being generally good for health for some time.
The researchers from the Columbia University Medical Center assessed participants' neurological health, and noted their dietary habits.
Their food intake was given a "Mediterranean Diet score" of between zero and nine.
During the course of the study, 262 people were diagnosed with Alzheimer's disease.
The researchers found that, for each additional point on the Mediterranean diet scale, the risk of Alzheimer's dropped by almost 10%.
Compared to the third of people who scored worst on the Mediterranean diet scores, those in the mid-ranking group had a 15% to 21% lower risk of developing Alzheimer's disease, and those with the highest score had a 39% to 40% lower risk.
The association remained significant even after the researchers adjusted their findings for age, gender, ethnicity, education, caloric intake, weight, smoking and other conditions.
The researchers accept their findings relied heavily on people's memories of what they ate, but said a tested dietary assessment technique had been used.
Dr Nicholas Scarmeas, who led the research, said: "Higher adherence to the Mediterranean diet is associated with a reduction in risk for Alzheimer's disease."
Professor Clive Ballard, director of research at the UK's Alzheimer's Society, said: "This large study in a leading journal adds to the growing weight of evidence that diet and lifestyle are very important risk factors for Alzheimer's disease.
"It makes an important contribution by suggesting that a strong adherence to a healthy diet can reduce the risk of developing Alzheimer's disease by as much as 40%, emphasising the importance of healthy eating.
"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 later life."