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A study of 4,523 U.S. adults who developed dementia found that people who were overweight or obese at diagnosis had lower mortality risk than those in the normal-weight range. The researchers say the finding may help inform prognosis, but the study does not establish that excess weight causes longer survival or that patients should gain weight.
People who were overweight or obese when diagnosed with dementia had a lower risk of death during follow-up than patients in the normal-weight range, according to a study by researchers at Columbia University and New York University. Published in the Journal of Alzheimer’s Disease, the analysis suggests that weight at diagnosis may offer information about survival, but it does not show that higher weight causes longer life or that patients should try to gain weight.
The researchers analyzed 4,523 adults in the U.S. Health and Retirement Study who had no dementia when they entered the study and later developed it. The ongoing study follows adults aged 51 and older; the data used for this analysis covered 1998 through 2022. Researchers were able to examine participants’ weight before and at diagnosis, then track survival after diagnosis.
Compared with people in the normal-weight range, those classified as overweight, with a body mass index (BMI) of 25 to 29.9, had a 16% lower risk of death. Participants with class 1 obesity, BMI 30 to 34.9, had a 27% lower risk; those with class 2 or 3 obesity, BMI of at least 35, had a 22% lower risk. These are relative differences in mortality risk reported by the study, not estimates of how many years longer individuals lived.
The researchers said the associations remained after accounting for factors including demographics, smoking and other chronic conditions. They also tested whether several potential biases could explain the pattern and reported that their additional analyses did not suggest those factors were significant contributors. The findings identify an association; they do not establish a biological cause.
Weight May Inform Survival Estimates
The results may help clinicians and families interpret weight at the time of dementia diagnosis as one piece of information about a patient’s health and potential survival. They also draw attention to nutrition, which can become difficult for people with dementia as symptoms affect appetite, initiative and the ability to eat independently.
That practical relevance should not be mistaken for a recommendation to increase weight. The study compared outcomes among people with different BMI levels; it did not test a weight-gain intervention, determine an ideal weight for people with dementia or show that obesity is beneficial overall. Obesity is associated with other health risks, including heart disease and diabetes, and this study does not overturn evidence that excess weight in midlife is associated with higher dementia risk.
The finding is also a reminder that a health measure can mean different things at different stages of life and illness. In this analysis, the association concerns survival after dementia diagnosis, not whether weight prevents dementia or improves symptoms.
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Why Researchers Tested for Bias
The result is counterintuitive because obesity is a risk factor for several chronic illnesses, and research has linked overweight or obesity in midlife with a higher likelihood of developing dementia later. Some earlier studies, however, have also reported better survival among people with dementia who have higher body weight. The Columbia and NYU team examined whether the apparent survival difference might arise from how people are selected or measured in studies.
One concern is that weight loss can precede a dementia diagnosis. The source report cites prior work by study authors Yuan Zhang and Virginia Chang indicating that weight loss may begin up to a decade before diagnosis and accelerate in the years immediately before it. If a study captures weight only once, people categorized as normal weight could include some whose weight has fallen as dementia develops, potentially complicating comparisons with people who remain heavier.
The researchers also considered selection-related explanations. Restricting an analysis to people who develop dementia can produce misleading associations, and people with obesity may die from other conditions before they are old enough to develop dementia. That could leave a comparatively healthier group of people with obesity in the dementia sample. The team reported that its checks did not find these examined biases to be significant explanations, while acknowledging that the reason for the association remains unresolved.
“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 University Mailman School of Public Health
weight management for dementia patients
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Cause and Clinical Use Remain Open
The study does not establish why higher BMI was associated with lower mortality. The researchers proposed possible physiological explanations, such as greater energy reserves or more muscle mass, but these remain possibilities rather than demonstrated mechanisms. The analysis also cannot show whether changing a person’s weight would change their survival.
The source report does not provide enough detail to determine how the reported risk differences translate into absolute mortality rates or additional years of life. It also does not establish how the association varies by dementia type, severity, treatment or specific nutrition status. Although the researchers tested several potential biases, those checks cannot rule out every unmeasured factor or fully settle the cause of the pattern.
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Further Work on Nutrition and Survival
The findings add evidence for researchers studying how weight changes around dementia diagnosis relate to later health. Further studies would need to clarify the possible biological pathways, examine weight trajectories and nutrition more closely, and determine whether the pattern holds across patient groups and dementia types.
For now, the study’s authors frame weight as a possible prognostic signal, not a treatment target. The analysis did not test a clinical strategy or change in diet, so its results alone do not support advising patients to gain weight. The paper reports support from the National Institutes of Health; the source material does not describe a planned follow-up study or a specific clinical guideline change.
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Key Questions
What did the study find?
Among 4,523 people who developed dementia, participants who were overweight or obese at diagnosis had lower mortality risk during follow-up than those in the normal-weight range. The study reported relative risk differences of 16% for overweight, 27% for class 1 obesity and 22% for class 2 or 3 obesity.
Does this mean people with dementia should gain weight?
No. The study was not designed to test whether gaining weight affects survival. Its first author, Virginia Chang, specifically cautioned that the findings do not mean patients should attempt to become overweight or obese.
Why might weight matter after a dementia diagnosis?
The researchers noted that dementia can be accompanied by reduced appetite, increased energy expenditure, weight loss and difficulty feeding oneself. They proposed that greater energy reserves or muscle mass could be relevant, but the study did not establish a mechanism.
How strong is the evidence?
The analysis followed a large group over time and adjusted for several factors, including chronic conditions, smoking and demographics. It remains an observational study, however, so it can identify an association but cannot prove that higher weight causes longer survival.
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