Abstract

Objective To examine the associations of cardiorespiratory fitness (hereafter fitness) and various obesity measures with risks of incident impaired fasting glucose (IFG) and type 2 diabetes.

Research design and methods Prospective cohort study of 14,006 men (7,795 for the analyses of IFG) free of an abnormal electrocardiogram, heart attack, stroke, cancer, and diabetes.

Results 3,612 (39,610 man-years) and 477 (101,419 man-years) men developed IFG and type 2 diabetes, respectively. Compared with the least fit 20% in multivariate analyses, IFG and type 2 diabetes risks in the most fit 20% were 14% and 52% lower, respectively (both P<0.001). Men with body mass index (BMI) ≥30.0, waist girth >102.0 cm, or % body fat ≥25 had 2.7-, 1.9-, and 1.3-fold higher risks for type 2 diabetes, respectively, compared with non-obese men (all P<0.01), and the results for IFG were similar. In the combined analyses, obese unfit (least fit 20%) men had 5.7-fold higher risk for type 2 diabetes compared with normal weight fit (most fit 80%) men. We observed similar trends for the joint associations of BMI and fitness with IFG, and those of waist girth or % body fat and fitness with both IFG and type 2 diabetes.

Conclusions Low fitness and obesity increased risks of IFG and type 2 diabetes by approximately similar magnitudes. When considered simultaneously, fitness attenuated but did not eliminate the increased risks of IFG and type 2 diabetes associated with obesity, and the highest risk was found in obese and unfit men.