From the Doctor's Desk: Body Weight and Alzheimer's Risk—Is There an Association?

January 5, 2012

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By Daniel C. Potts, MD
Tuscaloosa, Alabama

Body weight is a common topic of discussion in my neurology practice. In addition to the well-known association of excess weight with medical conditions like type II diabetes, there is also a link between obesity and obstructive sleep apnea, stroke, and other neurologic conditions. For instance, obesity in middle age predicts an increased risk of Alzheimer's disease in later life.

Recent findings, however, shed light on what may be an interesting paradox: in contrast to what has been shown in middle-aged persons, older people seem to have a lower risk of developing Alzheimer's disease if they are overweight.

In a recent study published in Neurology® by lead author Jeffrey M. Burns, M.D., from the University of Kansas Alzheimer's Disease Center, non-overweight individuals from age 60s to 80s who have no symptoms of Alzheimer's are more likely than their heavier peers to have biomarkers of Alzheimer's disease. These biomarkers are predictors for the later development of the disease.

In their analysis a lower body mass index (BMI) was associated with higher levels of biomarkers and a higher likelihood of having brain plaques and tangles, the predominant pathologic changes seen in the brains of Alzheimer's patients. Among people with mild cognitive impairment, for instance, 85 percent of non-overweight individuals had signs of these brain abnormalities, compared to just 48 percent of those who were overweight or obese. (A BMI of 25 or above is considered overweight.) This finding raises the possibility that weight loss or a low body mass index (BMI) later in life may be an early warning sign of mental decline.

Researchers have some theories about why there is a relationship between weight and Alzheimer's disease. Importantly, the relationship is a correlation and the studies don't address how one may cause the other.

For example, although Alzheimer's is traditionally thought of as a brain disease, it may have effects on the body that can present early on. Well before memory loss and other symptoms appear, Alzheimer's may trigger changes in metabolism that promote weight loss.

The relationship between weight loss and the progression of Alzheimer's may be a two-way street. People who start to experience declines in mental function may shop for groceries less regularly, cook less frequently, and eat less—and the poor nutrition that results could in turn accelerate the progression of the disease.

This new information emphasizes that good health practices help to prevent illness, and health practices may fall apart in the early stages of illness and accelerate cognitive and physical decline.

In my practice I still plan to provide extensive counseling to individuals who are overweight because the health benefits of weight loss in this group are clearly defined. However, these findings may make me more diligent about investigating cognitive function when I see persons over the age of 60 who have lost weight or who are underweight and about following them closely to monitor for emerging impairment.

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