Abstract
AIMS: Low mid-life fitness is associated with higher risk for heart failure (HF). However, it is unclear to what extent this HF risk is modifiable and mediated by the burden of cardiac and noncardiac comorbidities. We studied the effect of cardiac and noncardiac comorbidities on the association of mid-life fitness and fitness change with HF risk. METHODS: Linking individual subject data from the Cooper Center Longitudinal Study (CCLS) with Medicare claims files, we studied 19,485 subjects (21.2% women) who survived to receive Medicare coverage from 1999 to 2009. Fitness estimated by Balke treadmill time at mean age of 49 years was analyzed as a continuous variable (in metabolic equivalents [METs]) and according to age- and sex-specific quintiles. Associations of mid-life fitness and fitness change with HF hospitalization after age of 65 years were assessed by applying a proportional hazards recurrent events model to the failure time data with each comorbidity entered as time-dependent covariates. RESULTS: After 127,110 person years of Medicare follow-up, we observed 1,038 HF hospitalizations. Higher mid-life fitness was associated with a lower risk for HF hospitalization (hazard ratio [HR] 0.82 [0.76-0.87] per MET) after adjustment for traditional risk factors. This remained unchanged after further adjustment for the burden of Medicare-identified cardiac and noncardiac comorbidities (HR 0.83 [0.78-0.89]). Each 1 MET improvement in mid-life fitness was associated with a 17% lower risk for HF hospitalization in later life (HR 0.83 [0.74-0.93] per MET). CONCLUSIONS: Mid-life fitness is an independent and modifiable risk factor for HF hospitalization at a later age.