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A study of 4,523 U.S. adults who developed dementia found that those who were overweight or had obesity at diagnosis had a lower risk of death than those in the normal-weight range. The researchers say the association may make weight a useful prognostic signal, but the study does not show that gaining weight improves survival or explain why the association exists.
People who were overweight or had obesity when diagnosed with dementia had a lower risk of death than those in the normal-weight range, according to a study published in the Journal of Alzheimer’s Disease. The analysis found the association remained after researchers accounted for several demographic and health factors, but it does not establish that higher weight causes longer survival.
Researchers from Columbia University Mailman School of Public Health and NYU School of Global Public Health analyzed data on 4,523 adults who did not have dementia when they entered the study and later developed it. The participants were part of the U.S. Health and Retirement Study, which collects information on adults aged 51 and older. The researchers used the long-running data to examine weight before and at dementia diagnosis and survival afterward.
Compared with people in the normal-weight category, participants classified as overweight (body mass index, or BMI, of 25 to 29.9) had a 16% lower risk of death. The reported risk was 27% lower for people with class 1 obesity (BMI of 30 to 34.9) and 22% lower for those with class 2 or 3 obesity (BMI of 35 or higher). These are associations from the study, not evidence that weight gain would reduce an individual’s risk.
The researchers said the results persisted after adjustment for factors including chronic conditions, smoking and demographics. They also tested several potential sources of bias, including weight loss before diagnosis and the possibility that analyses limited to people who developed dementia could distort the relationship. Those checks did not indicate that the biases examined explained the observed association, though they cannot settle the cause.
Weight as a Prognostic Signal
The findings may help clinicians and researchers interpret weight at dementia diagnosis as one part of a person’s health picture. The authors say it could provide prognostic information about survival and draw attention to nutrition, which can become difficult to maintain as dementia affects appetite, motivation and the ability to eat independently.
The result is counterintuitive because obesity is linked to risks such as heart disease and diabetes, and higher weight in midlife is associated with greater likelihood of later dementia. The study addresses a different question: how weight recorded around diagnosis relates to survival among people who have already developed dementia. Its results should not be taken as a reason for patients to gain weight; the analysis did not test whether changing weight affects survival.
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Why Pre-Diagnosis Weight Matters
Earlier research has raised the possibility that weight loss can start well before dementia is diagnosed. The source report notes work by study authors Yuan Zhang and Virginia Chang indicating that weight loss may begin up to a decade before diagnosis and speed up in the years immediately before onset. A person recorded as normal weight at diagnosis could therefore have experienced a substantial decline from an earlier weight.
That possibility creates a challenge for studies relying on a single measurement. If weight loss reflects changes associated with advancing disease, then weight at diagnosis may capture more than a person’s long-term body size. The current analysis tracked weight over time and examined several potential biases, but the researchers say the reasons for the survival pattern remain unresolved.
The study was published in the Journal of Alzheimer’s Disease as “Body mass index and mortality in incident dementia.” The work was supported by the U.S. National Institutes of Health. Co-authors were Eleanor Hayes-Larson of the University of Southern California and Hui Zheng of the University of Toronto.
“Our analyses suggest that the major sources of bias we examined do not explain the survival advantage associated with higher weight.”
— Yuan Zhang, corresponding author and assistant professor at Columbia Mailman School of Public Health
The Cause Remains Unknown
The study found an association, but it did not establish why higher weight was linked to lower mortality. The authors suggest that greater energy reserves or muscle mass could potentially help people cope with wasting, reduced appetite or difficulties feeding themselves. These are possible explanations, not mechanisms confirmed by the analysis.
Although the researchers evaluated several forms of bias, the results cannot rule out every source of bias or show that the association applies equally to every person with dementia. The study also does not establish whether changing a person’s weight after diagnosis would alter survival. The reported percentages compare groups’ mortality risk; they are not estimates of how many years longer an individual may live.
Further Research on Nutrition
The next step is to clarify how weight changes before and after diagnosis relate to dementia severity, nutrition and survival. Studies that track those changes alongside factors such as muscle mass and eating difficulties could help distinguish a possible protective role for energy reserves from weight loss that signals illness progression.
For now, the researchers frame weight at diagnosis as a potential prognostic signal, not a treatment target. The study provides no recommendation for patients to gain weight, and it does not specify a change in clinical guidance. The underlying data span 1998 through 2022; any further evidence or guidance would depend on subsequent research and clinical evaluation.
Key Questions
What did the study find?
Among 4,523 people who developed dementia, those who were overweight or had obesity at diagnosis had a lower risk of death than those in the normal-weight category. The study found an association, not proof that higher weight caused longer survival.
How much lower was the reported risk?
Compared with the normal-weight group, the reported mortality risk was 16% lower for people who were overweight, 27% lower for class 1 obesity, and 22% lower for class 2 or 3 obesity. These figures describe group comparisons in this study, not an individual’s expected lifespan.
Does this mean people with dementia should gain weight?
No. The study was not designed to test whether gaining weight improves survival. First author Virginia Chang explicitly said the findings should not be interpreted as advice for patients to become overweight or obese.
Why might higher weight be associated with longer survival?
The researchers say the explanation is unknown. They discuss energy reserves or muscle mass as possible factors, while also noting that dementia can contribute to appetite loss, wasting and difficulty eating.
Source: rss
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