Co-evolving adiposity and frailty trajectories shape stroke risk in middle-aged and older adults.

Obesity and frailty are independently associated with stroke risk, but their joint longitudinal evolution and combined prognostic significance remain unclear. Using harmonized data from four nationally representative aging cohorts (China health and retirement longitudinal study [CHARLS], health and retirement study [HRS], English longitudinal study of aging [ELSA], and survey of health, aging and retirement in Europe [SHARE]), we applied group-based multi-trajectory modeling to 41,717 stroke-free participants aged ≥45 years to identify distinct joint body mass index (BMI)-frailty index trajectories. Five trajectory subgroups were identified in each cohort. Over a median follow-up of 11.0 years, the obesity and high-frailty group consistently demonstrated the highest stroke risk across all cohorts (hazard ratios [HRs], 2.86-7.87), whereas the overweight and low-frailty group showed protective associations (HRs, 0.42-0.60). High frailty was the dominant risk modifier within each BMI category. These findings were robust across extensive sensitivity analyses and indicate that joint BMI-frailty trajectory assessment provides superior stroke risk stratification compared with either measure alone.