The Med diet, rich in cereals, fruits, legumes and whole grains, fish and olive oil, has been linked to longer life, less heart disease, and protection against some cancers. The diet's main nutritional components include beta-carotene, vitamin C, tocopherols, polyphenols, and essential minerals.
The new cohort study, published on-line in the Annals of Neurology (April 18), followed 2258 elderly New Yorkers with no dementia for about four years. The diets of the subjects were measured using a semi-quantitative food frequency questionnaire, and a 'Mediterranean Diet' score was determined.
The researchers also gathered medical and neurological histories, performed physical and neurological exams, and interviewed each of the participants in-person. Subjects were reassessed every 18 months.
"Higher adherence to the Mediterranean diet was associated with significantly lower risk of developing Alzheimer's disease," wrote lead author Nikolaos Scarmeas from Columbia University Medical Center.
Scarmeas and his colleagues found that each increasing point on the Med diet score was linked with a 10 per cent drop in Alzheimer's risk.
Individuals whose diet closely resembled the Med diet had a 40 per cent lower risk of Alzheimer's than those who adhered the least to the diet. The association was still significant if the scientists adjusted the results to take into account factors like age, gender, ethnicity, BMI and smoking, for example.
The study has several limitations, including the use of food frequency questionnaires (FFQ) to determine dietary intakes. However, in this instance the scientists say that the FFQ would underestimate the effect.
Another limitation could be that people changed dietary habits throughout the four years of study. Again, the scientists argue that this would not change the results significantly since compliance to the diet appeared constant.
Professor Clive Ballard, director of research for British Charity, the Alzheimer's Society, said that the study made an important contribution to growing body of literature linking dietary lifestyle and the risk of Alzheimer's.
"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," said Ballard.
Professor Ballard emphasized that eating a healthy diet, regular exercise, and weight watching could reduce the risk of developing dementia in later life.
Alzheimer's disease is the most common form of dementia and currently affects over 13 million people worldwide. The direct and indirect cost of Alzheimer care is over $100 billion (€ 81 billion) in the US alone. The direct cost of Alzheimer care in the UK was estimated at £15 billion (€ 22 billion).