Importance of Achieving a "Fit" Cardiorespiratory Fitness Level for Several Years on the Incidence of Type 2 Diabetes Mellitus: A Japanese Cohort Study.

Background: The "Physical Activity Reference for Health Promotion 2013" provides "fit" reference values for cardiorespiratory fitness (CRF) for good health. The importance of achieving a fit CRF level for several years on the subsequent prevention of type 2 diabetes mellitus (T2DM) remains to be clarified. Methods: This cohort study was conducted in 2,235 nondiabetic males aged 21 to 59 years, enrolled in April 1986 through March 1987. We calculated the ratio of the area under the curve (AUC(ratio)) for actual measured values and the AUC for the reference values of CRF in each individual during an 8-year measurement period before the baseline. According to whether they met a fit CRF level or not, participants were categorized into groups based on the AUCratio (Fit(AUC) or Unfit(AUC)) and initial CRF (Fit(initial) or Unfit(initial)), respectively. T2DM was evaluated on health checkups until March 2010. Results: During the follow-up period, 400 men developed T2DM. After adjustment for confounders, as compared with those in the Fit(AUC) group, the hazard ratio (HR) for those in the Unfit(AUC) group was 1.33 (95% confidence interval [CI], 1.06-1.65). A combined analysis with the categories of initial value and AUC(ratio) showed that, compared with the Fit(initial) and Fit(AUC) group, the HRs of Fit(initial) and Unfit(AUC), Unfit(initial) and Fit(AUC), and Unfit(initial) and Unfit(AUC) groups were 1.41 (95% CI, 0.99-2.00), 1.18 (95% CI, 0.81-1.70), and 1.40 (95% CI, 1.08-1.83), respectively. Conclusion: Achievement of a fit CRF level established in the Japan physical activity guideline for several years was associated with lower subsequent risk of T2DM.