To investigate the association between different obesity phenotypes and the risk of dementia in an elderly health examination population.

Based on the health examination database of the Health Management (Examination) Center of the Affiliated Hospital of Chengdu University of Traditional Chinese Medicine from 2015 to 2025, participants were categorized according to body mass index (BMI) and metabolic health status into four groups: metabolically healthy non-obese (MHNO), metabolically healthy obese (MHO), metabolically unhealthy non-obese (MUNO), and metabolically unhealthy obese(MUO). The Fine-Gray competing risk model was used to evaluate the association between different obesity phenotypes and the cumulative risk of dementia, and subdistribution hazard ratios (SHR) with their 95% confidence intervals (CI) were calculated.

A total of 42 915 participants were eventually included, consisting of 17 015 in the MHNO group, 7 520 in the MHO group, 8 480 in the MUNO group, and 9 900 in the MUO group. Fine-Gray competing risk model analysis showed that, using the MHNO group as the reference, the risk of all-cause dementia, Alzheimer’s disease (AD), and vascular dementia(VD)showed an increasing trend with the severity of metabolic abnormalities and obesity. After full adjustment for confounding factors, the SHR(95% CI) for all-cause dementia was 1.102 (1.040-1.226) in the MHO group, 1.392 (1.257-1.542) in the MUNO group, and 1.725 (1.571-1.894) in the MUO group, with similar gradients observed for AD and VD risks. The results of sensitivity analysis were consistent with the main analysis.

A significant gradient association was observed between different obesity phenotypes and dementia risk, demonstrating a sequential increase in dementia risk with the severity of metabolic abnormalities and obesity. These findings highlight the need to prioritize the MUO population in dementia prevention and implement stratified intervention strategies for different phenotypes.