Association Between Midlife Cardiorespiratory Fitness and Risk of Stroke: The Cooper Center Longitudinal Study

Background and purpose: Low cardiorespiratory fitness (CRF) is associated with an increased risk of stroke. However, the extent to which this association is explained by the development of stroke risk factors such as diabetes mellitus, hypertension, and atrial fibrillation is unknown. We evaluated the relationship between midlife CRF and risk of stroke after the age of 65 years, independent of the antecedent risk factor burden.

Methods: Linking participant data from the Cooper Center Longitudinal Study with Medicare claims files, we studied 19 815 individuals who survived to receive Medicare coverage from 1999 to 2009. CRF estimated at baseline by Balke treadmill time was analyzed as a continuous variable (in metabolic equivalents) and according to age- and sex-specific quintiles (Q1=low CRF). Associations between midlife CRF and stroke hospitalization after the age of 65 years were assessed by applying a proportional hazards recurrent events model to the failure time data with hypertension, diabetes mellitus, and atrial fibrillation as time-dependent covariates.

Results: After 129 436 person-years of Medicare follow-up, we observed 808 stroke hospitalizations. After adjustment for baseline risk factors, higher midlife CRF was associated with a lower risk of stroke hospitalization (hazard ratio [HR], 0.61; 95% confidence interval [CI], 0.49-0.76; quintiles 4-5 versus 1]. This association remained unchanged after additional adjustment for burden of Medicare-identified stroke risk factors (hypertension, diabetes mellitus, and atrial fibrillation; HR, 0.63; 95% CI, 0.51-0.79; quintiles 4-5 versus 1).

Conclusions: There is a strong, inverse association between midlife CRF and stroke risk in later life independent of baseline and antecedent burden of risk factors, such as hypertension, diabetes mellitus, and atrial fibrillation.