Exploring severe mental illness and diabetes:protocol for a longitudinal observational and qualitative mixed methods study

Background: The average life expectancy for people with a severe mental illness (SMI) such as schizophrenia or bipolar disorder is 15-20 years less than for the population as a whole. Diabetes contributes significantly to this inequality, being 2-3 times more prevalent in people with SMI. Various risk factors have been implicated, including side effects of antipsychotic medication and unhealthy lifestyles, which often occur in the context of socio-economic disadvantage and healthcare inequality. However, little is known about how these factors interact to influence the risk of developing diabetes and poor diabetic outcomes, or how the organisation and provision of healthcare may contribute. Objective: The study aims to identify the determinants of diabetes and to explore variation in diabetes outcomes for people with SMI. Methods: This study will employ a concurrent mixed methods design combining the interrogation of electronic primary care health records from the Clinical Practice Research Datalink (CPRD GOLD) with qualitative interviews with adults with SMI and diabetes, their relatives/friends, and healthcare staff. The study has been funded for two years, from September 2017 to September 2019 and data collection has recently ended. Results: CPRD and linked health data will be used to explore the association of socio-demographic, illness and healthcarerelated factors with both the development and outcomes of Type 2 diabetes in people with SMI. Experiences of managing the comorbidity and accessing healthcare will be explored through qualitative interviews using topic guides informed by evidence synthesis and expert consultation. Findings from both datasets will be merged to develop a more comprehensive understanding of diabetes risks, interventions and outcomes for people with SMI. Findings will be translated into recommendations for interventions and services using co-design workshops. Conclusions: Improving diabetes outcomes for people with SMI is a high priority area nationally and globally. Understanding how risk factors combine to generate high prevalence of diabetes and poor diabetic outcomes for this population is a necessary first step in developing healthcare interventions to improve outcomes for people with diabetes and SMI.