Higher cumulative conicity index is associated with incident cardiometabolic multimorbidity across three international ageing cohorts

Most studies rely on single-time-point anthropometric measurements to assess abdominal adiposity, leaving the longitudinal association between cumulative exposure and incident cardiometabolic multimorbidity (CMM) unclear. This study examined the association between the cumulative conicity index (Cum-CI) and incident CMM across three international ageing cohorts. We included participants from the English Longitudinal Study of Ageing (ELSA; n = 1700), the Health and Retirement Study (HRS; n = 1620), and the China Health and Retirement Longitudinal Study (CHARLS; n = 3526). Using a landmark design, three prespecified survey waves with valid conicity index measurements were used to define the cumulative exposure period, and the third measurement wave was designated as the landmark time and time zero for follow-up. Participants who developed CMM before or at the landmark time were excluded. Cum-CI was calculated using the trapezoidal area-under-the-curve method and standardized separately within each cohort. Cohort-specific Cox proportional hazards models were used to estimate hazard ratios (HRs) for incident CMM per 1-standard-deviation increase in Cum-CI. Restricted cubic spline, subgroup, interaction, and sensitivity analyses were also conducted. During follow-up, 253 participants in ELSA, 332 in HRS, and 485 in CHARLS developed incident CMM. In the fully adjusted models, each 1-standard-deviation increase in cohort-specific Cum-CI was associated with a higher hazard of incident CMM in ELSA (HR 1.28; 95% confidence interval 1.10–1.49), HRS (HR 1.11; 95% confidence interval 1.03–1.20), and CHARLS (HR 1.31; 95% confidence interval 1.18–1.45). Restricted cubic spline (RCS) analyses showed no statistically significant evidence of nonlinearity in any cohort. Subgroup analyses showed limited evidence of effect modification, with a significant age interaction observed only in ELSA. Higher cohort-specific standardized Cum-CI was associated with a higher subsequent hazard of incident CMM across all three cohorts. Repeated assessment of the conicity index may help identify middle-aged and older adults with a greater cumulative burden of abdominal adiposity and a higher risk of developing CMM.