Cardiorespiratory fitness is not associated with reduced risk of prostate cancer: A cohort study and review of the literature

BACKGROUND: Cardiorespiratory fitness (CRF) has a strong inverse relationship with several chronic disease outcomes, including some cancers. The association between CRF and prostate cancer is controversial. We aimed to assess the prospective association of CRF with prostate cancer risk using a cohort study and review of the literature. MATERIAL AND METHODS: Cardiorespiratory fitness was assessed using a respiratory gas exchange analyser during exercise testing in 2204 cancer-free middle-aged men. Hazard ratios (HRs) with 95% confidence interval (CIs) were estimated. We corrected for within-person variability in CRF levels using repeat measurements. RESULTS: During a median follow-up of 24.9 years, 216 prostate cancer cases occurred. The age-adjusted regression dilution ratio of CRF was 0.58 (95% CI: 0.53-0.64). The HR (95% CI) of prostate cancer per 1 standard deviation increase in CRF in age-adjusted analysis was 1.10 (0.95-1.27). The association remained consistent after further adjustment for several risk factors (HR 1.13; 95% CI 0.96-1.33). The corresponding adjusted HRs were 1.24 (95% CI: 0.87-1.77) and 1.28 (95% CI: 0.87-1.88), respectively, when comparing the extreme tertiles of CRF levels. Previous studies mostly reported no evidence of an association or an increased risk of prostate cancer in relation to high CRF. Studies reporting positive associations had short-term follow-up durations (<10 years). CONCLUSIONS: Primary data and a review of previous studies suggest that elevated CRF is not associated with reduced prostate cancer risk. Previous findings of significant evidence of associations could be attributed to increased screening and detection as well as reverse causation bias.