Main and interactive effects of physical activity, fitness and body mass in the prevention of cancer from the Copenhagen Male Study.

Little knowledge exists about the role of cardiorespiratory fitness (CRF) or its interaction with excess adiposity determined by body mass index (BMI) in cancer prevention. A total of 5,128 middle-aged men, without a history of cancer at baseline in 1970-71, were examined for subsequent incidence and mortality of several cancer types. Participants' data were linked with cancer registration and mortality data to March 2017. During 47 years of follow-up, a total of 1,920 incident cases and 1,638 cancer-related deaths were ascertained. BMI, particularly obesity, was associated with (i) incidence and (ii) mortality from respiratory/thoracic cancers; and (iii) all cancer-cause mortality. The respective adjusted hazard ratios (HRs) were: (i) 0.51 (95%CI:0.32-0.79), (ii) 0.48 (95%CI:0.30-0.75) and (iii) 0.73 (95%CI:0.59-0.89) when compared obese men (BMI ≥30 kg/m) to men with healthy-BMI (<25 kg/m). Increasing CRF was inversely associated with incidence and mortality of respiratory/thoracic cancers, HRs 0.78 (95%CI:0.67-0.90) and 0.73 (95%CI:0.63-0.84) respectively; and all cancer-cause incidence 0.92 (95%CI:0.86-0.98) and mortality 0.85 (95%CI:0.79-0.91). Physical activity (PA) was not associated with most outcomes. We found no evidence of interactions between CRF or PA and BMI on cancer risk. This evidence suggests that midlife CRF is associated with lowered risk of cancer incidence and mortality with no evidence of cancer risk modification by BMI.