People who are overweight or obese when diagnosed with dementia have a significantly lower risk of death than those at a normal weight, according to a study published on 25 March 2026 in the Journal of Alzheimer’s Disease.
Researchers from the Columbia University Mailman School of Public Health and the NYU School of Global Public Health analyzed data from 4,523 participants in the Health and Retirement Study, a nationally representative study of U.S. adults ages 51 and older. The team examined records collected between 1998 and 2022, focusing on individuals who were free of dementia when entering the study but subsequently developed the condition.
The findings challenge expectations about weight and health because midlife obesity is an established risk factor for developing dementia. Once the condition has developed, however, higher body weight appears linked to better survival.
People classified as overweight, with a body mass index of 25 to 29.9, had a 16 percent lower risk of death compared to individuals in the normal weight range. Those with class 1 obesity, having a BMI of 30 to 34.9, experienced a 27 percent reduction in mortality risk. Individuals with class 2 or 3 obesity, with a BMI equal to or greater than 35, showed a 22 percent lower risk.
The researchers adjusted their calculations for smoking, existing medical conditions, and demographic characteristics. They also evaluated potential statistical distortions, including weight loss that frequently begins up to a decade before a dementia diagnosis and survivor bias.
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.
Yuan Zhang, assistant professor of Sociomedical Sciences at Columbia Mailman and in the Butler Columbia Aging Center
Researchers said that stored reserves could potentially help individuals tolerate periods of inadequate nutrition. Dementia can interfere with eating by altering brain processes that regulate appetite, increasing energy expenditure, or making self-feeding difficult.
Nutrition can be a big problem for people with dementia. 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.
Virginia Chang, associate professor of social and behavioral sciences at NYU School of Global Public Health
The study authors emphasized that the observational findings do not mean patients should attempt to gain weight. The research received funding from the National Institutes of Health under grant numbers R00AG070274 and R00AG075317.
“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,” said the study's lead author Chang.
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.
Virginia Chang, associate professor of social and behavioral sciences at NYU School of Global Public Health