Reduced risk of incident kidney cancer from walking and running.

PURPOSE: This study aimed to test whether incident kidney cancer risk is associated with exercise energy expenditure (i.e., metabolic equivalents, 1 MET) when calculated from distance walked or run.
METHODS: Hazard ratios (HR) and 95% confidence intervals (95% CI) from Cox proportional hazard analyses of self-reported physician-diagnosed incident kidney cancer versus MET-hours per week in 91,820 subjects recruited between 1991 and 1993 (7.7 yr follow-up of 42,833 subjects) and between 1998 and 1999 (6.4 yr follow-up of 33,053 subjects) as part of the National Runners' Health Study and between 1998 and 1999 as part of the National Walkers' Health Study (5.7 yr follow-up of 15,934 subjects).
RESULTS: Fifty-two incident cancers were reported. Age- and sex-adjusted risk declined 1.9% per MET-hour per week run or walked (HR = 0.981, 95% CI = 0.964-0.997, P = 0.02). Compared with walking or running below guidelines levels (<7.5 MET·h·wk(-1)), the risk for incident kidney cancer was 61% lower for meeting the guidelines (HR = 0.39, 95% CI = 0.11-1.08, P = 0.07 for 7.5-12.5 MET·h·wk(-1)), 67% lower for exercising one to two times the recommended level (HR = 0.33; 95% CI = 0.15-0.72, P = 0.005 for 12.6-25.1 MET·h·wk(-1)), and 76.3% lower for exercising two times or more the recommended level (HR = 0.24, 95% CI = 0.11-0.52, P = 0.0005 for ≥ 25.2 MET·h·wk(-1)). Incident kidney cancer risk also increased in association with baseline body mass index (P = 0.002), smoking (P = 0.02), and hypertensive (P = 0.007) and diabetes medication use (P = 0.01); however, exercise-associated reductions in kidney cancer risk persisted for 12.6-25.1 MET·h·wk(-1) (HR = 0.35, P = 0.01) and ≥ 25.2 MET·h·wk(-1) (HR = 0.29, P = 0.004) vis-à-vis <7.5 MET·h·wk(-1) when also adjusted for body mass index, hypertension, diabetes, and pack-years smoked.
CONCLUSION: Running and walking may reduce incident kidney cancer risk independent of its other known risk factors.