Population-based register study results published in Schizophrenia Research failed to find that the increase in diabetes associated with schizophrenia accounts for excess mortality in individuals with schizophrenia. Compared with the general population, patients with schizophrenia have a greater risk of developing diabetes and individuals with both diabetes and schizophrenia have a 3- to 4-fold higher mortality rate than individuals with diabetes alone.
Anita Toender, MS, of the National Centre for Register-based Research, Aarhus University, Denmark, and colleagues used nationwide registers to conduct a cohort study of 239,118 Danish patients with diabetes between 1997 and 2017. They estimated incidence rate ratios (IRR) of diabetic complications and all-cause and cause-specific mortality rate ratios (MRR) using Cox regression models and data on schizophrenia and diabetes diagnoses.
Women with schizophrenia and diabetes and those with diabetes alone had similar rates of diabetic complications (IRR, 0.93; 95% CI, 0.84-1.02); however this rate was significantly lower in men with schizophrenia and diabetes (IRR, 0.85; 95% CI, 0.78-0.92). All-cause mortality in individuals with a diabetic complication was significantly higher in patients with schizophrenia (MRR, 1.92 in females; MRR, 1.69 in males). Among those without diabetic complications, patients with schizophrenia also had a higher mortality rate (MRR, 2.01 in females; MRR, 1.71 in males).
The study had a number of limitations, including the inability to distinguish between type 1 and type 2 diabetes based on the information in the registers, the lack of data on blood glucose measurements, and the exclusion of individuals who were not diabetic from the study, which may have underestimated effect sizes.
The researchers noted, “Surprisingly, individuals with schizophrenia and diabetes did not have a higher incidence of diabetic complications compared to those with diabetes only.” They theorized that the study could have missed the real occurrence of diabetic complications by focusing on registered hospital diagnoses. They added that many patients with both schizophrenia and diabetes may not live long enough to develop the longer-term complications of the disease.
Toender A, Vestergaard M, Munk-Olsen T, Larsen JT, Kristensen JK, Laursen TM. Risk of diabetic complications and subsequent mortality among individuals with schizophrenia and diabetes—a population-based register study [published online February 3, 2020]. Schizophrenia Res. doi:10.1016/j.schres.2020.01.024