Association of body mass index with all-cause mortality in patients with diabetes: a systemic review and meta-analysis.

Abstract

The obesity paradox phenomenon has been found in different populations, such as heart failure and coronary heart disease, which suggest that patients with established cardiovascular disease (CVD) and with normal weight had higher risk of mortality than those with overweight or obesity. However, the obesity paradox is controversial among patients with diabetes which has been considered as the coronary heart disease equivalent. The aim of our study was to summarize current findings on the relationship between body mass index (BMI) and all-cause mortality in patients with diabetes and make a meta-analysis. We searched previous studies from MEDLINE, EMBASE, and the Cochrane databases using the keywords: BMI, mortality, diabetes, and obesity paradox or reverse epidemiology. Finally, sixteen studies were identified and 385,925 patients were included. Patients were divided into five groups based on BMI (kg/m(2)) levels: underweight (<18.5), normal weight (18.5-24.9), overweight (25-29.9), mild obesity (30-34.9), and morbid obesity (>35). A random effect meta-analysis was performed by the inverse variance method. As compared with the normal weight, the underweight had higher risk of mortality [hazard ratio (HR): 1.59, 95% confidence interval (CI): 1.32-1.91]. In contrast, the overweight and the mild obesity had lower risk of mortality than the normal weight (HR: 0.86, 95% CI: 0.78-0.96, and 0.88, 95% CI: 0.78-1.00, respectively), but the morbid obesity did not (HR: 0.99, 95% CI: 0.84-1.16). In addition, the subgroup analysis by sex showed that the overweight had the lowest mortality as compared with the normal weight (HR: 0.82, 95% CI: 0.74-0.90) and the obesity in males, but the risk of mortality did not differ among groups in females. Notably, the heterogeneity was significant in most of group comparisons. Our meta-analysis showed a U-shaped relationship between BMI and all-cause mortality in patients with diabetes. The significant heterogeneity among studies suggested that many confounders such as sex difference may affect the association.