Cardiorespiratory Fitness and Colorectal Cancer Incidence in US Veterans: A Cohort Study.

[OBJECTIVE] To evaluate the association between cardiorespiratory fitness (CRF), objectively measured by standardized exercise treadmill test (ETT), and colorectal cancer incidence.

[METHODS] The study involved 643,583 US veterans nationwide (41,968 women) from the Exercise Testing and Health Outcomes Study (ETHOS) cohort. None had cancer diagnosis before ETT or had cancer other than colorectal after ETT. Participants completed an ETT (Bruce) with no evidence of ischemia and were stratified into CRF categories (quintiles) based on peak metabolic equivalents (METs) achieved: least fit (n=119,673; METs: 4.8±1.5), low fit (n=157,059; METs: 7.3±1.4), moderate fit (n=122,194; METs: 8.6±1.4), fit (n=170,324; METs: 10.5±1.0), and high fit (n= 74,333; METs: 13.6±1.8).

[RESULTS] During a median follow-up period of 10.0 years, totaling 6,632,561 person-years, 8190 participants had colorectal cancer (12.4 events per 10,000 person-years). Cardiorespiratory fitness was inversely associated to colorectal cancer risk, independent of comorbidities, with a 9% risk reduction per 1-MET higher in CRF (hazard ratio [HR], 0.91; 95% CI, 0.90 to 0.92), for men and women and across all races. Compared with least fit, the risk of those in the next CRF category (low fit) was 14% lower (HR, 0.86; 95% CI, 0.81 to 0.91). The risk declined progressively with increased CRF and was 57% lower (HR, 0.43; 95% CI, 0.29 to 0.48) for those in the high-fit group.

[CONCLUSION] We observed an inverse and graded association between CRF and colorectal cancer incidence, across races and sexes, independent of comorbidities. The lower risk was evident in those with a peak CRF of approximately 8.5 to 10.5 METs, a relatively moderate CRF status attainable by most middle-aged and older individuals.