BioEd Online

It seems a diet loaded with fruit, vegetables and olive oil, some fish and alcohol, but little dairy and meat — known as the Mediterranean diet — can reduce the risk of Alzheimer's disease in the elderly.

Dementia caused by Alzheimer's disease has a huge impact on the US population: about 5% of those aged 65 to 74, and nearly half of those older than 85 are diagnosed with the disease's symptoms.

Experts have long thought that diet plays a role in the disease, but studies of single ingredients from fish to vitamin B have proven inconclusive. Neurologist Nikolaos Scarmeas of Columbia University, New York, wondered if looking at broader dietary trends might be more informative.

Scarmeas followed more than 2,000 cognitively normal elderly people from Manhattan, with an average age of 77 years, for about four years. Every 18 months the participants filled out a dietary questionnaire asking them about what they consumed and how often. In total, 262 of the participants developed Alzheimer's during the course of the study.

The top third of participants who adhered most closely to a Mediterranean diet (eating three times as much fish and less than a third as much dairy as others) had a 39-40% lower risk of developing Alzheimer's disease than the bottom third, the researchers report in the Annals of Neurology¹. Even the middle tier had a 15-20% lower risk than this bottom third.

Food for thought

This is just a first hint that a Mediterranean diet might protect against dementia, says Scarmeas. "It's premature to make recommendations, as the findings need to be replicated in other studies and reports," he says. There is a risk that people lie about their food habits in studies based on questionnaires, for example, although Scarmeas says "these biases and errors are not big enough to overreach our results".

The Mediterranean diet has already been shown to protect against coronary heart disease, diabetes and some forms of cancer. How it might prevent Alzheimer's is unknown.

Scarmeas guesses the effect might be down to the antioxidants, anti-inflammatories or protective vascular ingredients found in several of the components of a Mediterranean diet. He plans to use brain-imaging studies to unpick what is going on.

In the meantime, Scarmeas says, he'll be sticking to his cereals, fruit and vegetables. "I'm Greek so I follow it. That's what I used to eat when I was young — not only for health purposes, but because I like it."

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