Associations Between Metabolic Heterogeneity of Obesity and Chronic Multimorbidity Progression: A Nationwide Prospective Cohort Study

AIM: To explore the impact of BMI-metabolic phenotypes and their changes on chronic multimorbidity. METHODS: Data were drawn from the China Health and Retirement Longitudinal Study (CHARLS), with participants aged ≥ 45. Analysing the metabolic heterogeneity of obesity through four BMI-metabolic phenotypes: metabolically healthy normal weight (MHNW), metabolically unhealthy overweight/obesity (MUOO), metabolically healthy overweight/obesity (MHOO), and metabolically unhealthy normal weight (MUNW). Transition of BMI-metabolic phenotype was assessed between 2011 and 2015. Chronic multimorbidity refers to the coexistence of ≥ 2 chronic diseases among 14 specified diseases. The association between changes in BMI-metabolic phenotypes and chronic multimorbidity was applied using Cox regression. RESULTS: Among 2528 individuals, the median age was 56.00 years, and 1244 (49.21%) had chronic multimorbidity. After adjusting for all variables at baseline, participants in the MUOO phenotype exhibited a 1.66-fold increased risk of chronic multimorbidity compared with the MHNW phenotype (95% CI: 1.42-1.94, p < 0.001), followed by the MUNW phenotype with a 1.25-fold increased risk (95% CI: 1.06-1.47, p = 0.008). However, in the MHOO phenotype, no statistically significant association was found (p > 0.05), which may reflect its heterogeneity and instability as a transient rather than benign metabolic state. In addition, obesity or unhealthy metabolism can also increase the risk of chronic multimorbidity. CONCLUSIONS: Overall, for individuals aged ≥ 45, especially those with the MUOO phenotype, managing body weight and improving metabolic health are crucial for preventing chronic multimorbidity.