Purpose Although the benefit of high cardiorespiratory fitness (CRF) for the prevention of type 2 diabetes mellitus (T2DM) is widely accepted, whether consistently high CRF is necessary or transiently high CRF is sufficient is unclear. The present study was conducted to examine the hypothesis that consistently high level of CRF is more beneficial than transiently high CRF for the prevention of T2DM. Methods This cohort study was conducted in nondiabetic 7158 men age 20 to 60 yr, enrolled from 1986 to 1987. The area under the curve with respect to ground (AUCG) for CRF measurements during an 8-yr measurement period (1979-1987) was calculated as an index of integrated CRF level during the period. The differences (ΔAUCP) between AUCG and peak AUC (peak CRF-measurement period) was also calculated as an index of the presence and the size of a "spike" in CRF. T2DM was defined by fasting blood glucose and a self-reported diagnosis of diabetes for participants with blood tests. For participants without blood tests, T2DM was defined by the result of oral glucose test after a nonfasting urinary test and a self-reported diagnosis of diabetes. T2DM was determined on health checkups until 2009. Results During the follow-up period, 1495 men developed T2DM. After adjustment for confounders, as compared with the first quartile of AUCG for CRF, the hazard ratio (95% confidence interval) for the second, third, and fourth quartiles were 0.87 (0.76 to 1.00), 0.80 (0.68 to 0.95), and 0.72 (0.58 to 0.89), respectively. For CRF spike, there was no association between ΔAUCP in CRF and the incidence of T2DM. Conclusions Consistently higher level of CRF over time was associated with lower risk of T2DM.
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