People who are overweight or obese when they are diagnosed with dementia are likely to live longer than those in a normal weight range, according to a new study published in the Journal of Alzheimer’s Disease .
While the underlying reasons are not fully understood, the findings suggest that one’s weight status at the time of a dementia diagnosis may provide meaningful prognostic information about survival and underscore the need for greater attention to nutrition among those with dementia.
“This doesn’t mean that patients with dementia should attempt to become overweight or obese, as our study was not designed to test that question. But our findings do suggest that weight status may serve as a useful prognostic signal for survival at the time of dementia diagnosis. They also support the notion that nutrition is a key factor in the health and survival of people with dementia,” said Virginia Chang , associate professor of social and behavioral sciences at NYU School of Global Public Health and the study’s lead author.
Obesity is a risk factor for a range of illnesses, including heart disease and diabetes. It’s also been shown that people who are overweight or obese at midlife are more likely to develop dementia later in life. Yet some studies show that among those diagnosed with dementia, obesity is associated with improved survival.
Researchers have wondered if these counterintuitive findings point to an underlying reason why excess weight may help people with dementia live longer—for instance, having greater energy reserves—or if they are the result of biases in the data.
One potential bias may result from the fact that people with dementia often lose weight well before they are diagnosed, with a study by Chang and collaborator Yuan Zhang showing that weight loss can begin up to a decade before diagnosis and accelerate in the years right before the disease’s onset. So, if a study only captures weight at one time point and does not consider weight loss prior to a dementia diagnosis, it’s possible that people considered normal weight may include those with more advanced disease who are at higher risk of death.
Other types of bias could arise because a study includes only people who developed dementia, which can create misleading associations between weight status and mortality. Another possibility is “survivor” bias: because people with obesity may be at risk of dying earlier from other conditions before developing dementia, it’s possible that only a comparatively healthier subset of people live long enough to be studied.
In this study, Chang, Zhang, and their colleagues used data from the Health and Retirement Study, an ongoing, nationally representative study of US adults 51 and older conducted by the University of Michigan. Using data collected from 1998 through 2022, the study included 4,523 individuals who were dementia-free when they first entered the study and later developed dementia. Given the long timespan of the study, the researchers could track individuals’ weight before and at their dementia diagnosis, as well as how long they lived after being diagnosed.
The researchers found that people with dementia who were overweight or obese at the time of diagnosis had a significantly lower mortality risk than those of normal weight, even after adjusting for factors such as other chronic conditions, smoking, and demographics. Individuals who were overweight (body mass index of 25 to 29.9) had a 16-percent lower risk of death, while those with class 1 obesity (BMI of 30 to 34.9) had a 27-percent lower risk, and those with class 2 and 3 obesity (BMI equal to or greater than 35) had a 22-percent lower risk.
Importantly, additional analyses evaluating several forms of potential bias did not suggest that they were significant contributors to the observed associations between weight status and mortality.
From a physiological standpoint, the researchers describe why excess weight could benefit people with dementia, including having greater catabolic reserves in the form of energy stores or more muscle mass.
“Nutrition can be a big problem for people with dementia,” said Chang. “They may experience wasting and an inability to eat, which can be due to changes in the brain’s central drive, leading to loss of appetite and initiative, increased energy expenditure, and difficulties feeding themselves.”
“Because this finding is somewhat counterintuitive, an important question is whether it could simply be an artifact of bias. Our analyses suggest that the major sources of bias we examined do not explain the survival advantage associated with higher weight,” said Yuan Zhang, assistant professor of sociomedical sciences at Columbia University’s Mailman School of Public Health.
“While our analysis examined several forms of bias, and there are very plausible physiological reasons for the potential benefits of a little extra weight in this context, we still don’t know exactly why people who were overweight or obese had a lower risk of death. Regardless of the underlying mechanism, however, weight status at the time of a dementia diagnosis can still serve as a meaningful prognostic signal,” noted Chang.
Additional study authors include Eleanor Hayes-Larson of the University of Southern California and Hui Zheng of the University of Toronto. This work was supported by the National Institutes of Health (grant numbers R00AG070274, R00AG075317).
Journal of Alzheimer’s Disease
Body mass index and mortality in incident dementia
30-Sep-2026