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||Cardiorespiratory fitness and risk of prostate cancer: findings from the Aerobics Center Longitudinal Study.
||Byun W, Sui X, Hébert JR, Church TS, Lee IM, Matthews CE, Blair SN
||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 20-82years, 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.