Journal of Alzheimer's Disease: Obesity at Dementia Diagnosis Associated with 27% Lower Mortality Risk

The reasons remain unclear, but the results suggest that body weight at diagnosis may provide valuable prognostic information about survival and highlight the need for greater attention to nutrition in people with dementia.

“This does not mean that patients with dementia should try to gain weight — our study was not designed to investigate that question. But the findings suggest that weight can serve as a useful prognostic indicator at the time of diagnosis. They also reinforce the importance of nutrition as a key factor in health and survival in dementia,” said lead author Virginia Chang of New York University's School of Global Public Health.

Obesity is a risk factor for many diseases, including heart disease and diabetes. It is also well established that people who are overweight in midlife are more likely to develop dementia later in life. However, some studies have found that among people already diagnosed with dementia, obesity is associated with better survival.

The researchers sought to determine whether these counterintuitive findings reflected a genuine effect — such as greater energy reserves — or resulted from biases in the data. One possible source of bias is that people with dementia often lose weight long before diagnosis, sometimes as early as a decade beforehand. As a result, those classified as having a “normal weight” may include patients whose disease is already more advanced.

Chang, Zhang and their colleagues used data from the Health and Retirement Study, an ongoing nationally representative study of American adults aged 51 and older conducted by the University of Michigan. They analyzed data collected between 1998 and 2022, including 4,523 people who did not have dementia initially but developed the condition later. The extended follow-up period allowed the researchers to track participants' weight before and at diagnosis, as well as their lifespan afterward.

The results showed that people with dementia who were overweight or had obesity at the time of diagnosis had a significantly lower risk of death than those with a normal weight, even after adjustments for chronic diseases, smoking and demographic factors. Compared with participants in the normal-weight range, those who were overweight (BMI 25–29.9) had a 16% lower risk of death. The risk was 27% lower among those with class I obesity (BMI 30–34.9) and 22% lower among those with class II or III obesity (BMI 35 or higher).

Additional analyses examining several potential sources of bias found no evidence that these factors substantially affected the observed associations.

From a physiological perspective, the researchers suggest that excess weight may offer an advantage in dementia by providing greater reserves to draw on during periods of increased metabolic demand, in the form of stored energy or muscle mass.

“Because this finding is somewhat counterintuitive, an important question is whether it is simply an artifact. Our analyses suggest that the main sources of bias we examined do not explain the survival advantage associated with higher body weight,” said Yuan Zhang of Columbia University's Mailman School of Public Health.

The researchers examined several potential forms of bias. Although plausible physiological explanations exist for why a modest amount of excess weight might be beneficial, the precise mechanism underlying the lower risk of death among patients with obesity remains unclear. Nevertheless, the authors emphasized that body weight at the time of a dementia diagnosis may still serve as a meaningful prognostic indicator.