Severe Mental Illness and Type 2 Diabetes Outcomes and Complications: A Nationwide Cohort Study

OBJECTIVE To compare cardiovascular and mortality outcomes in people with severe mental illness (SMI) versus no mental illness in a national cohort study of people with type 2 diabetes. RESEARCH DESIGN AND METHODS We included adults diagnosed with type 2 diabetes between 2004 and 2018 from the national Scottish diabetes register, ascertaining history of mental illness from linked psychiatric and general hospital admission records. We identified major cardiovascular disease (CVD) events, all-cause mortality, and CVD-specific mortality through record linkage. Using Cox regression, we estimated hazard ratios (HRs) for associations between SMI and outcomes, adjusting for baseline sociodemographic and clinical characteristics, including history of CVD, comorbidity, hypertension, high cholesterol, HbA1c, BMI, alcohol use disorder, and smoking. RESULTS Among 259,875 people with type 2 diabetes, 1.0%, 0.5%, and 3.0% had schizophrenia, bipolar disorder, and major depression, respectively. After adjusting for sociodemographic characteristics, the risk of major CVD events was higher in people with schizophrenia (HR 1.22, 95% CI 1.06–1.41), bipolar disorder (HR 1.58, 95% CI 1.33–1.87), and major depression (HR 1.59, 95% CI 1.49–1.70) compared with people without a history of mental illness. SMI was also associated with an approximately twofold increased risk of CVD-specific and all-cause mortality. All associations attenuated following further adjustment for clinical characteristics. CONCLUSIONS Among people with diabetes, people with a history of SMI have poorer cardiovascular and mortality outcomes compared with those without mental illness. While the underlying mechanisms are further investigated, effective prevention and management of cardiovascular risk factors is needed in this high-risk group.