Abstract
Based on self-reported physical activity, there is epidemiologic evidence for a beneficial relation between physical activity and colon cancer in men, but findings for other cancers are inconclusive. Measured cardiorespiratory fitness (CRF) can provide knowledge about the cancer-preventive value of physical activity. We aimed to assess relationships between CRF and risk of site-specific cancers. A cohort of 1997 healthy Norwegian men, aged 40-59 years at inclusion in 1972-1975, was followed for cancer throughout 2012 using data from the Cancer Registry of Norway. CRF was measured by a maximal exercise bicycle test at inclusion. Relationships between CRF and site-specific cancers were estimated using Cox regression, adjusted for age, body mass index, and smoking. During follow-up, 898 cancer cases were diagnosed in 758 men. When comparing men in CRF tertile 1 with men in tertiles 2 and 3, respectively, we found decreased risk of proximal colon cancer in tertile 2 (HR: 0.30, 95% CI: 0.13-0.73) and decreased risk of cancers of lung (0.39 95% CI: 0.22-0.66), pancreas (0.32 95% CI: 0.10-1.00), and bladder (HR: 0.40 95% CI: 0.21-0.74) in tertile 3. Furthermore, a significant trend for lower risk by increasing CRF tertile was found for cancers of proximal colon, lung, and bladder (P-value for trend <0.05). For other cancer sites, no significant association was found. Our results indicate that high midlife CRF may have cancer-preventive value.