Mediterranean Diet, Physical Activity, Cognitive Function, and Dementia Risk

From Journal Watch > Journal Watch Neurology

Gad A. Marshall, MD

Abstract
Two new studies addressed whether diet and physical activity in elders affect cognitive decline and dementia.

Introduction
In two large, prospective, population-based studies, researchers examined whether better adherence to a Mediterranean-type diet, with or without greater physical activity, is associated with less global cognitive decline or lower incidence of Alzheimer disease.

Scarmeas and colleagues investigated the association between amount of physical activity, alone or in combination with adherence to a Mediterranean-type diet, and incidence of Alzheimer disease (AD). For a mean of 5.4 years, the investigators followed 1880 community-dwelling, nondemented elders in New York City. Approximately every 1.5 years, participants completed physical-activity and food-frequency questionnaires and underwent cognitive and clinical assessments to determine dementia onset. A total of 282 participants developed AD. After adjustments for multiple confounders (including age, education, sex, ethnic background, presence of apolipoprotein E ε4 gene, baseline cognitive function, body-mass index, caloric intake, leisure activities, medical comorbidities, and smoking), the risk for AD was lower in participants with a high diet score (hazard ratio, 0.60), high physical activity (HR, 0.67), or both (HR, 0.65).

Féart and colleagues investigated the associations of adherence to a Mediterranean-type diet with cognitive decline and with dementia incidence. The investigators followed 1410 community-dwelling, nondemented elders from Bordeaux, France. Participants completed a food-frequency questionnaire and underwent cognitive tests and clinical assessments at least twice during a 5-year period. A total of 99 participants developed dementia (66 AD). After adjustment for potential confounders (including age, education, sex, marital status, presence of apolipoprotein E ε4 gene, physical activity, energy intake, multiple medications intake, depression, stroke, and cardiovascular risk factors), less cognitive decline on the Mini-Mental State Examination (but not in individual cognitive domains) was associated with greater adherence to a Mediterranean-type diet (measured as a continuous variable), whereas reduction in dementia risk was not.

Comment
In the New York study, both the Mediterranean-style diet and physical activity reduced dementia risk, whereas in the Bordeaux study, the diet helped maintain global cognitive function but did not affect dementia risk. The Bordeaux study may have been underpowered. On the other hand, the New York study had a high percentage of Latino and black participants, and therefore the findings may not generalize well to the rest of the U.S. or the world. Moreover, as an editorial author notes, whether these late-life lifestyle modifications reflect midlife lifestyle changes is unclear, thus further confounding the results.

Most dementia prevention or treatment interventions being investigated consist of new investigational drugs or supplements. Too few large, prospective, carefully designed population studies have tested the extent to which common midlife and late-life lifestyle modifications affect cognitive function and dementia risk. We need larger, longer-duration, prospective population studies and clinical trials of such lifestyle modifications. Results of these studies can be used to better educate patients earlier in life and to reinforce such common-sense interventions