Type-2 diabetes mellitus in schizophrenia: Increased prevalence and major risk factor of excess mortality in a naturalistic 7-year follow-up

Abstract

Objective Physical co-morbidity including type 2 diabetes mellitus is more prevalent in patients with schizophrenia compared to the general population. However, there is little consistent evidence that co-morbidity with diabetes mellitus and/or other diseases leads to excess mortality in schizophrenia. Thus, we investigated whether co-morbidity with diabetes and other somatic diseases is increased in schizophrenics, and if these are equally or more relevant predictors of mortality in schizophrenia than in age- and gender-matched hospitalised controls. Methods During 2000–2007, 679 patients with schizophrenia were admitted to University Hospital Birmingham NHS Trust. Co-morbidities were compared with 88,778 age- and gender group-matched hospital controls. Predictors of mortality were identified using forward Cox regression models. Results The prevalence of type 2 diabetes mellitus was increased in schizophrenia compared to hospitalised controls (11.3% versus 6.3%). The initial prevalence of type 2 diabetes mellitus was significantly higher in the 100 later deceased schizophrenic patients (24.0%) than in those 579 surviving over 7 years (9.2%). Predictors of mortality in schizophrenia were found to be age (relative risk [RR] = 1.1/year), type 2 diabetes mellitus (RR = 2.2), pneumonia (RR = 2.7), heart failure (RR = 2.9) and chronic renal failure (RR = 3.2). The impact of diabetes mellitus on mortality was significantly higher in schizophrenia than in hospital controls (RR = 2.2 versus RR = 1.1). In agreement, deceased schizophrenics had significantly suffered more diabetes mellitus than deceased controls (24.0 versus 10.5%). The relative risks of mortality for other disorders and their prevalence in later deceased subjects did not significantly differ between schizophrenia and controls. Conclusion Schizophrenics have more and additionally suffer more from diabetes: co-morbidity with diabetes mellitus is increased in schizophrenia in comparison with hospital controls; type 2 diabetes mellitus causes significant excess mortality in schizophrenia. Thus, monitoring for and prevention of type 2 diabetes mellitus is of utmost relevance in hospitalised patients with schizophrenia.