Abstract

Objective: To determine the independent and joint associations of cardiorespiratory fitness (CRF) and body mass index (BMI) with the incidence of type 2 diabetes in women.

Research Design and Methods: An observational cohort of 6,249 women aged 20 to 79 years was free of baseline cardiovascular disease, cancer, and diabetes. CRF was measured using a maximal treadmill exercise test. BMI (kg/m²) was computed from measured height and weight. Incidence of type 2 diabetes was identified primarily by 1997 American Diabetes Association criteria.

Results: During a 17-year follow-up, 143 cases of type 2 diabetes occurred. Compared with the least fit third, the multivariate (including BMI)-adjusted hazard ratio (HR) (95% confidence interval [CI]) was 0.86 (0.59-1.25) for the middle third, and 0.61 (0.38-0.96) for the upper third of CRF. For BMI, compared with normal weight patients, the multivariate (including CRF)-adjusted HR (95% CI) was 2.34 (1.55-3.54) for overweight individuals and 3.70 (2.12-6.44) for obese individuals. In the combined analyses, overweight/obese unfit (the lowest third of CRF) women had significantly higher risks, compared with normal weight fit (the upper two thirds of CRF) women.

Conclusions: Low CRF and higher BMI were independently associated with incident type 2 diabetes. The protective effect of CRF was observed in individuals who were overweight or obese, but CRF did not eliminate the increased risk in these groups. These findings underscore the critical importance of promoting regular physical activity and maintaining normal weight for diabetes prevention.