Cardiorespiratory fitness is not associated with risk of venous thromboembolism: a cohort study

Objectives. The inverse and independent association between cardiorespiratory fitness (CRF) and arterial thrombotic disease is well established. However, the potential association between CRF and venous thromboembolism (VTE) is not well known. We aimed to assess the prospective association of CRF with the risk of VTE. Design. Cardiorespiratory fitness, as measured by maximal oxygen uptake (VO_2max), was assessed using a respiratory gas exchange analyser in 2,249 men aged 42-61 years without a history of VTE at baseline in the Kuopio Ischemic Heart Disease prospective cohort. Cox-regression models were used to calculate hazard ratios (HR) with 95% confidence interval (CI) for VTE. We corrected for within-person variability in CRF levels using data from repeat measurements taken several years apart. Results. There were 144 (6.4%) incident VTE events recorded during a median follow-up of 25.2 years. The age-adjusted regression dilution ratio of CRF was 0.58 (95% CI: 0.53-0.64). The risk of VTE did not significantly decrease per 1 standard deviation increase in CRF in age-adjusted analysis (HR 0.90; 95% CI 0.75-1.08). The association remained consistent in analyses adjusted for several established and emerging risk factors (HR 0.90; 95% CI 0.73-1.12). The corresponding adjusted HRs were 0.80 (95% CI: 0.52-1.23) and 0.82 (95% CI: 0.51-1.32) respectively, when comparing the extreme tertiles of CRF levels. Conclusions. In a middle-aged Caucasian male population, CRF was not associated with future risk of VTE. Further studies are required to confirm and to generalize these findings, particulary in women and other age groups.