Independent and joint associations of non-exercise cardiorespiratory fitness and obesity with risk of type 2 diabetes mellitus in the Rural Chinese Cohort Study

An association between cardiorespiratory fitness (CRF) and type 2 diabetes mellitus (T2DM) has not been established in the Chinese population. This study aimed to estimate the independent and joint associations of CRF and obesity with T2DM incidence in the rural Chinese population.We conducted a prospective study of 11,825 non-T2DM subjects among rural Chinese adults. Cox regression models were used to estimate the independent and joint associations between CRF and obesity exposure on T2DM. Restricted cubic splines were used to model the dose-response association. During a median follow-up of 6.01 years, 835 participants developed T2DM. In comparison to quartile 1 of CRF, the multivariate hazard ratios (HRs) and 95% confidence intervals (CIs) of quartiles 2, 3, 4 were 0.75 (0.61-0.91), 0.54 (0.43-0.68), and 0.42 (0.32-0.55), respectively. When stratified by sex, the results were similar. Joint analyses showed that overweight/obesity-unfit individuals had a 2.28 times higher risk of developing T2DM than the normal weight-fit referent (HR 2.28, 95% CI 1.84-2.83; Pinteraction <0.001). The risk for the overweight/obesity-fit category (HR 1.61, 95% CI 1.21-2.15) was larger than for the normal weight-unfit category (HR 1.38, 95% CI 0.97-1.95) versus the normal weight-fit referent. Similar joint associations for waist circumference and CRF with T2DM were also observed.A negative association was observed between CRF and risk of T2DM. Overweight/obese or abdominal obesity and unfit participants showed the highest risks of T2DM. It is therefore strongly recommended that fitness-enhancing be encouraged for the prevention of T2DM, especially among obesity participants.