Estimated cardiorespiratory fitness and incident cardiometabolic multimorbidity: findings from three nationally representative cohorts.

OBJECTIVE: Cardiorespiratory fitness is a modifiable marker of cardiometabolic health, but its association with cardiometabolic multimorbidity (CMM) and the generalisability of that association across populations remain unclear. We examined the association between estimated cardiorespiratory fitness (eCRF) and incident CMM in three nationally representative cohorts. MATERIALS AND METHODS: We used data from the China Health and Retirement Longitudinal Study, the English Longitudinal Study of Ageing, and the US Health and Retirement Study. eCRF was derived from a validated sex-specific non-exercise equation and modelled per 1-SD increment and as sex-specific categories. CMM was defined as the coexistence of two or more of hypertension, diabetes, heart disease, and stroke. Associations were assessed using Cox proportional hazards models, with supplementary analyses of proportional hazards, competing death, multiple imputation, prediction performance, and meta-analysis. RESULTS: Among 12,944 participants, 3,029 developed incident CMM. Each 1-SD increment in eCRF was associated with a lower risk in the pooled model (hazard ratio 0.61, 95% CI 0.58-0.64). Compared with low fitness, high fitness was associated with a substantially lower risk (hazard ratio 0.40, 95% CI 0.35-0.45; P for trend <0.001). Adding eCRF to sociodemographic and behavioural predictors improved discrimination, and the association remained directionally consistent across sensitivity analyses. CONCLUSIONS: Higher estimated cardiorespiratory fitness was independently associated with a lower risk of incident CMM across three diverse populations and provided modest incremental prognostic information. As an easily obtained, non-exercise measure, eCRF may help characterise cardiometabolic risk in ageing populations, although between-cohort heterogeneity and the observational design warrant cautious interpretation.