Cardiorespiratory fitness and risk of prostate cancer: Findings from the Aerobics Center Longitudinal Study

Objective: To examine the association between cardiorespiratory fitness (CRF) and risk of incident prostate cancer (PrCA). Methods: Participants were 19,042 male subjects in the Aerobics Center Longitudinal Study (ACLS), ages 20–82 years, who received a baseline medical examination including a maximal treadmill exercise test between 1976 and 2003. CRF levels were defined as low (lowest 20%), moderate (middle 40%), and high (upper 40%) according to age-specific distribution of treadmill duration from the overall ACLS population. PrCA was assessed from responses to mail-back health surveys during 1982–2004. Cox proportional hazards regression models, adjusted for potential confounders, were used to compute hazard ratios (HRs), 95% confidence intervals (95% CIs), and incidence rates (per 10,000 person-years of follow-up). Results: A total of 634 men reported a diagnosis of incident PrCA during an average of 9.3 ± 7.1 years of follow-up. Adjusted HRs (95% CIs) in men with moderate and high CRF relative to low CRF were, 1.68 (1.13–2.48) and 1.74 (1.15–2.62), respectively. The positive association between CRF and PrCA was observed only in the strata of men who were not obese, had ≥1 follow-up examination, or who were diagnosed ≤1995. Conclusions: Rather than revealing a causal relationship, the unexpected positive association observed between CRF and incident PrCA is most likely due to a screening/detection bias in more fit men who also are more health-conscious. Results have important implications for understanding the health-related factors that predispose men to receive PrCA screening that may lead to over-detection of indolent disease.