The development of type 2 diabetes management in people with severe mental illness in the Capital Region of Denmark from 2001 to 2015

Background Type 2 diabetes (T2D) treatment has changed markedly within the last decades. We aimed to explore whether people with severe mental illness (SMI) have followed the same changes in T2D treatment as those without SMI, as multiple studies suggest that people with SMI receive suboptimal care for somatic disorders. Methods In this registry‐based annual cohort study, we explored the T2D treatment from 2001 to 2015 provided in general practices of the Greater Copenhagen area. We stratified the T2D cohorts by their pre‐existing SMI status. T2D was defined based on elevated glycated hemoglobin (≥48 mmol/mol) or glucose (≥11 mmol/L) using data from the Copenhagen Primary Care Laboratory Database. Individuals with schizophrenia spectrum disorders (ICD‐10 F20–29) or affective disorders (bipolar disorder or unipolar depression, ICD‐10 F30–33) were identified based on hospital‐acquired diagnoses made within 5 years before January 1 each year for people with prevalent T2D or 5 years before meeting our T2D definition for incident patients. For comparison, we defined a non‐SMI group, including people who did not have a hospital‐acquired diagnosis of schizophrenia spectrum disorders, affective disorders, or personality disorders. For each calendar year, we assembled cohorts of people with T2D with or without SMI. We used Poisson regression to calculate the rates per 100 person‐years of having at least one biochemical test (glycated hemoglobin, low‐density lipoprotein cholesterol, estimated glomerular filtration rate, and urine albumin‐creatinine ratio), having poor control of these biochemical results, taking glucose‐lowering or cardiovascular medications, or experiencing a clinical outcome, including all‐cause mortality and cardiovascular mortality. Three outcomes (cardiovascular events, cardiovascular mortality, and all‐cause mortality) were additionally examined and adjusted for age and sex in a post hoc analysis. Results From 2001 to 2015, 66,914 individuals were identified as having T2D. In 2015, 1.5% of the study population had schizophrenia spectrum disorder and 1.4% had an affective disorder. The number of people who used biochemical tests or had poor biochemical risk factor control was essentially unrelated to SMI status. One exception was that fewer LDL cholesterol tests were done on people with affective disorders and schizophrenia spectrum disorders at the beginning of the study period compared to people in the non‐SMI group. This difference gradually