Cardiovascular disease and mortality in patients with type 2 diabetes after bariatric surgery in Sweden: a nationwide, matched, observational cohort study

Background In patients with diabetes and obesity specifically, no studies have examined mortality after bariatric surgery. We did a nationwide study in Sweden to examine risks of cardiovascular disease and mortality in patients with obesity and diabetes who had undergone bariatric surgery (Roux-en-Y gastric bypass [RYGB]). Methods In this nationwide, matched, observational cohort study, we merged data for patients who had undergone RYGB registered in the Scandinavian Obesity Surgery Registry with other national databases, and identified matched controls (on the basis of sex, age, BMI, and calendar time [year]) who had not undergone bariatric surgery from the National Diabetes Registry. We assessed risks of cardiovascular disease and death using a Cox proportional-hazards regression model and other methods to examine the treatment effect while accounting for residual confounding. Primary outcomes were total mortality, cardiovascular death, and fatal or non-fatal myocardial infarction. Findings Between Jan 1, 2007, and Dec 31, 2014, we obtained data for 6132 patients who had undergone RYGB and 6132 control patients who had not. Median follow-up was 3.5 years (IQR 2.1-4.7). We noted a 58% relative risk reduction (hazard ratio [HR] 0.42, 95% CI 0.30-0.57; p< 0.0001) in overall mortality in the RYGB group compared with the controls. The risk of fatal or non-fatal myocardial infarction was 49% lower (HR 0.51, 0.29-0.91; p= 0.021) and that of cardiovascular death was 59% lower (0.41, 0.19-0.90; p= 0.026) in the RYGB group than in the control group. 5 year absolute risks of death were 1.8% (95% CI 1.5-2.2) in the RYGB group and 5.8% (5.0-6.8) in the control group. Interpretation Our findings provide support for the benefits of RYGB surgery for patients with obesity and type 2 diabetes. The causes of these beneficial effects may be the weight reduction per se, changes in physiology and metabolism, improved care and treatment, improvements in lifestyle and risk factors, or combinations of these factors.