Mediterranean Diet May Protect Against Mild Cognitive Impairment

Marlene Busko

February 13, 2009

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February 13, 2009 — Elderly individuals who follow a healthy Mediterranean diet are less likely to develop mild cognitive impairment (MCI) and also less likely to convert from MCI to Alzheimer's disease (AD), researchers report.

"A healthy diet may not only affect your risk for AD but also your risk for getting MCI and converting from MCI to AD," lead author Nikolaos Scarmeas, MD, Columbia University Medical Center, New York, told Medscape Psychiatry.

However, these preliminary findings need to be replicated in a randomized trial, he cautioned.

"Based on this single study, we cannot make dietary recommendations, but it adds to accumulating evidence that in addition to affecting cardiovascular and other diseases, diet also affects brain function," he said.

The study, based on data from the Washington Heights-Inwood Columbia Aging Project (WHICAP) study, is published in the February issue of the Archives of Neurology.

Can Diet Delay Dementia?

Normal aging implies that cognitive performance may be worse than that of younger individuals but as good as one's peers, said Dr. Scarmeas. An individual with MCI, on the other hand, performs worse on neuropsychological tests compared with his or her peers. About 10% to 15% of individuals with MCI convert to AD each year, he added.

Previously researchers reported that adherence to a Mediterranean diet was linked with a reduced risk for AD, but its effect on developing MCI was unknown.

To investigate whether cognitively normal individuals whose food intake was more typical of a Mediterranean diet were less likely to develop MCI, the researchers analyzed data from 1393 cognitively normal individuals and 484 individuals with MCI who were participants in the WHICAP multiethnic community study in New York. Participants had a mean age of 77 years.

The study outcomes were incidence of MCI and progression of MCI to AD.

To be classed as having MCI, subjects were required to have a subjective memory complaint, objective impairment in at least 1 cognitive domain, essentially preserved activities of daily living, and no diagnosis of dementia.

Study participants were given a score of 0 to 9 based on their adherence to a Mediterranean diet, where 9 indicated greatest adherence to this diet.

Strong adherence to a Mediterranean diet was characterized by a high intake (at the median or higher) of fish, fruit, vegetables, legumes, cereals, and unsaturated fat; a low intake of dairy products and meat; and a moderate intake of alcohol.

Based on their adherence to a Mediterranean diet, subjects were divided into 3 groups: 609 participants with low adherence, 775 with middle adherence, and 491 with high adherence to a Mediterranean diet.

Lower Risk for Incident MCI

In a mean follow-up of 4.5 years, 275 of the 1393 cognitively normal individuals developed MCI.

Compared with the cognitively normal subjects in the lowest Mediterranean-diet–adherence group, subjects in the middle group had a 17% lower risk of developing MCI, and subjects with the highest adherence to the diet had a 28% lower risk of developing MCI.

Risk for Incident MCI Among Cognitively Normal Elderly Subjects

Mediterranean Diet Tertile HR (95% CI) P
Low 1.00 NA
Middle 0.83 (0.62 – 1.12) .24
High 0.72 (0.72 – 1.00) .05

Lower Risk of Progressing from MCI to AD

In a mean follow-up of 4.3 years, 106 of the 482 individuals with MCI went on to develop AD.

Compared with the subjects with MCI in the lowest Mediterranean-diet–adherence group, those in the middle group had a 45% lower risk of progressing to AD, and subjects with the highest adherence had a 48% lower risk of progressing to AD.

Risk for Incident AD Among Elderly Subjects with MCI

Mediterranean Diet Tertile HR (95% CI) P
Low 1.00 NA
Middle 0.55 (0.34 – 0.90) .02
High 0.52 (0.30 – 0.91) .02

Potential Mechanisms Need to be Elucidated

There is strong evidence relating the Mediterranean diet to a lower risk for vascular risk factors such as dyslipidemia, hypertension, and coronary heart disease, the authors write.

Higher adherence to a Mediterranean diet seems to improve carbohydrate metabolism and significantly reduces plasma glucose levels, serum insulin levels, and insulin resistance, which may explain its beneficial effects on lowering incident MCI, they add.

Alternatively, the protective effect of the Mediterranean diet on MCI may be mediated via inflammatory pathways, it may be related to oxidative stress, or it may be the result of some individual food component.

"Exploration of such [biological] mechanisms and potential future interventional studies will provide a more complete and convincing picture of the conceivably important role of a healthy diet in the risk of cognitive impairment and AD," they write.

No financial disclosure was reported. The work was supported by the National Institute on Aging.

Arch Neurology. 2009;66:216-225. Abstract

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