Abstract
Objective: To investigate the associations between non-exercise estimated cardiorespiratory fitness (eCRF) and the incidence of urinary tract cancer overall, along with the site-specific incidence of bladder and kidney cancers within a large prospective cohort of Norwegian adults.
Methods: This prospective cohort study used the second survey of the Nord-Trøndelag Health Study (HUNT2), conducted between 1995 and 1997. 46 968 cancer-free adults who had complete data on eCRF at baseline were included. eCRF was determined using two sex-specific prediction models based on age, waist circumference, resting heart rate, and self-reported physical activity. eCRF was further classified into age-specific quintiles (based on a 10-year interval) within each sex group and merged into 3 categories: 20% low, 40% medium, and 40% high. Information about cancer diagnosis was obtained from the Cancer Registry of Norway. We used the Cox proportional hazards models to estimate hazard ratios (HR) and 95% confidence intervals (CI) after adjusting for important confounders.
Results: Over a median follow-up of 22.2 years, there were 652, 381, and 255 incidents of urinary tract, bladder, and kidney cancers, respectively. Medium and high levels of eCRF were associated with lower incidence of urinary tract cancer in the total cohort (HR = 0.64, 95% CI: 0.51–0.79 and HR = 0.87, 95% CI: 0.71–1.05, P-value for trend <0.001), and especially among men (HR = 0.83, 95% CI: 0.66–1.04 and HR = 0.59, 95% CI: 0.46–0.76, P-value for trend <0.001). Only the high eCRF level was associated with a lower incidence of bladder cancer in men (HR = 0.66, 95% CI: 0.48–0.90), but no association was found in women (HR = 0.93, 95% CI: 0.52–1.66). The P-value of the Likelihood Ratio Test for effect modification by sex = 0.027. There was a clear and inverse dose-response association between eCRF and kidney cancer in the total cohort (P-value for trend <0.001) and specifically in men (P-value for trend <0.001). The high eCRF level was also associated with a reduced incidence of kidney cancer among women (HR = 0.52, 95% CI: 0.28–0.96).
Conclusion: Higher levels of eCRF were associated with a lower incidence of both urinary tract and kidney cancers in the total cohort and especially among men. Also, only the high eCRF level was associated with a lower incidence of bladder cancer in men. Future studies with larger sample sizes are needed to explore the potential roles of eCRF in preventing these cancers among women.
