Risk of mortality and complications in patients with schizophrenia and diabetes mellitus: population-based cohort study

Background Schizophrenia patients have markedly elevated prevalence of diabetes compared with the general population. However, risk of mortality and diabetes-related complications among schizophrenia patients with co-occurring diabetes is understudied. Aims We investigated whether schizophrenia increased the risk of overall mortality, complications and post-complication mortality in people with diabetes. Method This population-based, propensity-score matched (1:10) cohort study identified 6991 patients with incident diabetes and pre-existing schizophrenia and 68 682 patients with incident diabetes only between 2001 and 2016 in Hong Kong using a medical record database of public healthcare services. Association between schizophrenia and all-cause mortality was examined with a Cox proportional hazards model. Effect of schizophrenia on first-year complication occurrence following diabetes diagnosis and post-complication mortality rates were evaluated. Results Schizophrenia was associated with increased all-cause mortality (adjusted hazards ratio [aHR] 1.11, 95% CI 1.05-1.18), particularly among men and older age groups. Schizophrenia patients with diabetes had higher metabolic complication rate (aHR 1.99, 95% CI 1.63-2.42), lower microvascular complication rate (aHR 0.75, 95% CI 0.65-0.86) and comparable macrovascular complication rate (aHR 0.93, 95% CI 0.85-1.03), relative to patients with diabetes only. Among patients with diabetes complications, schizophrenia was associated with elevated all-cause mortality after macrovascular (aHR 1.19, 95% CI 1.04-1.37) and microvascular (aHR 1.33, 95% CI 1.08-1.64) complications. Gender-stratified analyses revealed that a significant effect of schizophrenia on heightened post-complication mortality was observed in men only. Conclusions Schizophrenia patients with co-occurring diabetes are at increased risk of excess mortality, including post-complication mortality. Further research identifying effective interventions is warranted to optimise diabetes-related outcomes in this vulnerable population.