NEW population-based data have revealed that being overweight or obese when diagnosed with dementia is associated with lower mortality than normal weight, prompting fresh questions about how body mass index (BMI) relates to dementia prognosis and mortality risk.
Investigators examined the association between weight status at incident dementia and mortality in a large, US population-based sample with extended follow-up. Weight status was categorised by BMI, with normal weight as the reference category and overweight, class I obesity and class II/III obesity as comparison categories.
Dementia at each wave was assessed based on respondent or proxy-based assessments of cognitive function using the Langa-Weir classification, and incident dementia was defined as a transition from no dementia to dementia between waves.
The outcome of interest was mortality following incident dementia. The researchers also evaluated potential sources of bias affecting this association, including confounding due to weight loss, collider stratification bias and survivor bias.
Compared with the normal weight category, class I obesity at incident dementia was associated with a 27% lower risk of mortality (hazard ratio [HR] 0.73, 95% confidence interval [CI]: 0.62 to 0.86).
Overweight and class II/III obesity were also associated with lower mortality.
Analyses evaluating potential sources of bias did not support confounding due to weight loss, collider stratification bias or survivor bias as major contributors to the observed associations.
In this large US population-based sample with extended follow-up, overweight and obesity at incident dementia have been associated with lower mortality relative to normal weight. The underlying mechanisms are not fully understood and warrant further investigation. These findings suggest that weight status at diagnosis may serve as a useful prognostic indicator alongside other factors. Because these data are observational, higher BMI should not be viewed as protective, and weight status is best considered one prognostic factor among many in clinical practice.
Reference
Chang VW et al. Body mass index and mortality in incident dementia. Journal of Alzheimer’s Disease. 2026;0(0)
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