Background: The aim of this study is to investigate the independent and joint effects of cardiorespiratory fitnes (CRF) and body mass index (BMI) on cancer mortality in a low body mass index population Methods: We evaluated CRF and BMI in relation to cancer mortality in 8760 Japanese men. The median BMI wa 22.6 kg/m2 (IQR: 21.0-24.3). The mean follow-up period was more than 20 years. Hazard ratios and 95% CI wer obtained using a Cox proportional hazards model while adjusting for several confounding factors Results: Using the 2nd tertile of BMI (21.6-23.6 kg/m2) as reference, hazard ratios and 95% CI for the lowest tertil of BMI (18.5-21.5) were 1.26 (0.87-1.81), and 0.92 (0.64-1.34) for the highest tertile (23.7-37.4). Using the lowes tertile of CRF as reference, hazard ratios and 95% CIs for 2nd and highest tertiles of CRF were 0.78 (0.55-1.10) an 0.59 (0.40-0.88). We further calculated hazard ratios according to groups of men cross-Tabulated by tertiles of CR and BMI. Among men in the second tertile of BMI, those belonging to the lowest CRF tertile had a 53% lower ris of cancer mortality compared to those in the lowest CRF tertile (hazard ratio: 0.47, 95% CI: 0.23-0.97). Among thos in the highest BMI tertile, the corresponding hazard ratio was 0.54 (0.25-1.17) Conclusion: These results suggest that high CRF is associated with lower cancer mortality in a Japanese populatio of men with low average BMI.
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