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

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 7years (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.