The Obesity Paradox in Type 2 Diabetes Mellitus: Relationship of Body Mass Index to Prognosis

BACKGROUND: Whether obesity is associated with a better prognosis in patients with type 2 diabetes mellitus is controversial. OBJECTIVE: To investigate the association between body weight and prognosis in a large cohort of patients with type 2 diabetes followed for a prolonged period. DESIGN: Prospective cohort. SETTING: National Health Service, England. PATIENTS: Patients with diabetes. MEASUREMENTS: The relationship between body mass index (BMI) and prognosis in patients with type 2 diabetes without known cardiovascular disease at baseline was investigated. Information on all-cause mortality and cardiovascular morbidity (such as the acute coronary syndrome, cerebrovascular accidents, and heart failure) was collected. Cox regression survival analysis, corrected for potential modifiers, including cardiovascular risk factors and comorbid conditions (such as cancer, chronic kidney disease, and lung disease), was done. RESULTS: 10,568 patients were followed for a median of 10.6 years (interquartile range, 7.8 to 13.4). Median age was 63 years (interquartile range, 55 to 71), and 54% of patients were men. Overweight or obese patients (BMI >25 kg/m²) had a higher rate of cardiac events (such as the acute coronary syndrome and heart failure) than those of normal weight (BMI, 18.5 to 24.9 kg/m²). However, being overweight (BMI, 25 to 29.9 kg/m²) was associated with a lower mortality risk, whereas obese patients (BMI >30 kg/m²) had a mortality risk similar to that of normal-weight persons. Patients with low body weight had the worst prognosis. LIMITATION: Data about cause of death were not available. CONCLUSION: In this cohort, patients with type 2 diabetes who were overweight or obese were more likely to be hospitalized for cardiovascular reasons. Being overweight was associated with a lower mortality risk, but being obese was not. PRIMARY FUNDING SOURCE: National Institute for Health Research and University of Hull.