Body mass index, diabetes, and mortality in French women: explaining away a “paradox”

Background: Obesity is associated with increased mortality in the general population but, paradoxically, with decreased mortality in persons with diabetes. Methods: Among 88,373 French women participating in the E3N-EPIC study who were free of diabetes in 1990, we estimated the hazard ratios (HRs) and 95% confidence intervals (CIs) of mortality for body mass index (BMI) levels by diabetes status. Results: During an average 16.7 years of follow-up, 2421 cases of diabetes were identified and 3750 deaths occurred. For overweight/obese versus normal-weight women, the HR of mortality was 1.42 (95% CI = 1.32―1.53) in women without diabetes and 0.69 (0.40―1.18) in women with incident diabetes. As BMI increased, mortality among women without diabetes increased and that among women with diabetes decreased. Conclusions: We found the obesity "paradox" among women with and without incident diabetes in the same population. Selection bias may be a simple explanation for this "paradox."