Obesity's link to lower risk of death in dementia points to likely importance of nutrition

by Columbia University's Mailman School of Public Health

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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 by Columbia University Mailman School of Public Health and NYU School of Global Public Health. The findings suggest that 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.

The results are published in the Journal of Alzheimer's Disease.

A counterintuitive survival advantage

Obesity is a risk factor for a range of illnesses, including heart disease and diabetes. Studies have also 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.

"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 corresponding author Yuan Zhang, Ph.D., assistant professor of sociomedical sciences at Columbia Mailman and in the Butler Columbia Aging Center.

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% lower risk of death, while those with class 1 obesity (BMI of 30 to 34.9) had a 27% lower risk and those with class 2 and 3 obesity (BMI equal to or greater than 35) had a 22% lower risk.

"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 first author.

Tracking weight and testing for bias

Zhang, Chang and their colleagues used data from the Health and Retirement Study, an ongoing, nationally representative study of U.S. adults ages 51 and older. Their analysis of data collected from 1998 through 2022 included 4,523 individuals who were dementia-free when they first entered the study and later developed dementia.

Given the long time span 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.

Researchers have wondered if the study's 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 Zhang and Chang 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 before a dementia diagnosis, it is 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 is possible that only a comparatively healthier subset of people live long enough to be studied.

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.

Nutrition and the limits of interpretation

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."

Although the analysis examined several forms of bias and there are plausible physiological reasons for the potential benefits of a little extra weight in this context, why people who were overweight or obese had a lower risk of death remains unanswered.

Regardless of the underlying mechanism, however, weight status at the time of a dementia diagnosis can still serve as a meaningful prognostic signal, according to Zhang and Chang.

Additional co-authors are Eleanor Hayes-Larson of the University of Southern California and Hui Zheng of the University of Toronto.

Publication details

Virginia W. Chang et al, Body mass index and mortality in incident dementia, Journal of Alzheimer's Disease (2026). DOI: 10.1177/13872877261491694

Journal information: Journal of Alzheimer's Disease

Key medical concepts

ObesityDementiaMortality RiskOverweightNutrition

Clinical categories

NeurologyHealthy agingWeight management Provided by Columbia University's Mailman School of Public Health Who's behind this story?

Sadie Harley

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