Overweight and dementia risk

Dementia News 71, March 2007

An interesting paper by the group of Richard Mayeux at the Columbia University in New York explores the association between measures of adiposity, Alzheimer's disease (AD) and dementia associated with stroke (DAS). The rationale for this study lies in the observation that obesity is related to vascular disease and stroke, and the authors were interested in distinguishing the association of adiposity to dementias with and without a vascular component.

The authors followed for 5 years several hundreds of persons 65 years or older, without dementia at the time of enrollment, measuring body mass index (BMI, 893 persons) waist circumference (WC, 907 persons), and weight change (709 persons). Participants were enrolled in this longitudinal study by random sampling of Medicare recipients 65 years or older residing in northern Manhattan.

During the follow up period there were 181 incident dementia cases, 112 AD and 53 DAS. Dementia was ascertained using standard methods. The results published by the Columbia University group suggest that high adiposity may be associated with higher dementia risk, particularly in younger elderly. It is worth to remind that high adiposity predicts hyperinsulinemia and diabetes, both putative dementia risk factors.

However, low weight and weight loss due to pre-clinical disease acted as confounders and the association was attenuated in older age groups. These observations make the association not linear and may explain why previous studies have reported conflicting results on the relationship between BMI and risk of dementia.

In particular, the authors found a U-shape association between BMI and dementia in the younger elderly, while higher BMI was related to lower dementia risk in the oldest old. The results are somewhat consistent with literature data showing that the association of high BMI to cardiovascular and general mortality is attenuated in older age groups. Therefore a high BMI may constitute a risk factors for several diseases, including dementia, in younger people while becomes a predictor of decreased mortality in the oldest old.

The authors also found that higher waist circumference (WC), a better measure of adiposity in the elderly, was associated to higher DAS risk for all age groups. The association was stronger for DAS compared to AD. Moreover, WC was associated with higher AD risk in younger elderly but not in the oldest group, once again stressing the complexity of the association of the measured parameters with dementia.

As a whole, the impression from this paper, as well as from other literature published in the last couple of years, is that in the middle aged and in the younger old people overweight and adiposity are indeed contributing to AD and other dementias risk, possibly by increasing metabolic and vascular risk. In contrast, in the oldest group a lower weight and adiposity or the loss of weight have a negative prognostic value. The results reported by the Columbia University group underscore the importance of longitudinal studies to better assess the effect of the risk factors on the development of dementia and also suggest that interventions aimed at promoting healthy life style habits have a better chance to be an effective prevention measure if undertaken during adult life and, possibly, early aging.

prof. Stefano Govoni
Department of Experimental and Applied Pharmacology, University of Pavia, Italy

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