Background: In "Physical Activity Reference for Health Promotion 2013" the Japan Ministry of Health, Labour and Welfare publication gives reference values for cardiorespiratory fitness (CRF) required for good health. We examined the associations between the CRF reference values and incidence of type 2 diabetes. Methods: This prospective cohort study enrolled 4633 nondiabetic Japanese men aged 20 to 39 years at baseline. CRF was measured using the cycle ergometer test, and maximal oxygen uptake was estimated. On the basis of the CRF reference value, participants were classified into 2 groups: those with values less than the reference value (under-RV) and those with values equal to or greater than reference value (over-RV). Hazard ratios (HRs) and 95% CIs for incident type 2 diabetes were estimated using a Cox proportional hazards model. Results: A total of 266 participants developed type 2 diabetes during the 14 years of follow-up. As compared with the under-RV group, the over-RV group had a significantly lower multivariable-adjusted HR for type 2 diabetes (HR 0.67; 95% CI, 0.51-0.89). In receiver operating characteristic analysis, the optimal CRF cut-off value for predicting incident type 2 diabetes was 10.8 metabolic equivalents (sensitivity, 0.64; specificity, 0.64), which was close to the CRF reference value of 11.0 metabolic equivalents. Conclusions: The reference CRF value appears to be reasonably valid for prevention of type 2 diabetes, especially among Japanese men younger than 40 years. Development of type 2 diabetes can be prevented by maintaining a CRF level above the reference value.
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