Long‐term weight maintenance and risk of cardiometabolic multimorbidity and its subtypes in middle‐aged and older adults: A pooled landmark analysis in China and the <scp>UK</scp>

AIMS: Cardiometabolic multimorbidity (CMM) is a growing global health challenge. Traditional body mass index (BMI) metrics, such as baseline values or simple change, fail to capture the dynamic nature of long-term weight maintenance. We aimed to evaluate the association between time in target range for BMI (TTR-BMI)-a composite metric of weight stability and magnitude-and the risk of incident CMM and its subtypes in middle-aged and older adults. MATERIALS AND METHODS: We conducted a pooled analysis of 9167 participants aged ≥45 years from two prospective cohorts: the China Health and Retirement Longitudinal Study (CHARLS) and the English Longitudinal Study of Ageing (ELSA). A landmark analysis design was employed to minimise immortal time bias. TTR-BMI was calculated via linear interpolation based on cohort-specific normal weight ranges. Multivariable Cox proportional hazards models estimated hazard ratios (HRs) and 95% confidence intervals (CIs) for incident CMM, adjusting for sociodemographics, lifestyle factors, baseline BMI, and pre-existing cardiometabolic burden. RESULTS: During the follow-up period, higher TTR-BMI was linearly associated with a lower risk of incident CMM. In fully adjusted models, each 1-SD increase in TTR-BMI was associated with a lower risk of CMM (HR 0.896, 95% CI 0.845-0.950). Compared with participants "never in range" (TTR = 0), those "always in range" (TTR = 1) had a 23.8% lower risk of CMM (HR 0.762, 95% CI 0.669-0.868). Subtype analysis revealed that the inverse association was most pronounced for metabolic-dominant phenotypes, particularly the co-occurrence of diabetes and dyslipidaemia (HR 0.76, 95% CI 0.59-0.98). The associations were robust across cohorts and stronger in men and individuals aged ≥60 years. CONCLUSIONS: Higher TTR-BMI is an independent predictor of lower CMM risk in middle-aged and older adults, offering superior prognostic value for metabolic multimorbidity patterns. These findings highlight the clinical importance of prioritising long-term weight maintenance within a target range, rather than single time-point assessments, as a key strategy for delaying the onset of cardiometabolic disease.