Diabetes complication burden and patterns and risk of mortality in people with schizophrenia and diabetes: A population-based cohort study with 16-year follow-up

Abstract

Schizophrenia is associated with increased prevalence of diabetes. However, risk of diabetes complications as well as the impact of complication burden and patterns on subsequent mortality risk in schizophrenia patients with co-existing diabetes is understudied. This population-based, propensity-score matched (1:10) cohort study identified 6991 patients with incident diabetes and pre-existing schizophrenia and 68,682 patients with incident diabetes only (comparison group) between 2001 and 2016 in Hong Kong, using territory-wide medical-record database of public healthcare services. Complications were measured by Diabetes Complications Severity Index (DCSI), which stratified complication burden into 6 levels (DCSI score=0, 1, 2, 3, 4, or ≥5). Associations of diabetes complications, in terms of DCSI scores (complication burden), specific types and two-way combinations of complications (complication patterns), with all-cause mortality rate in schizophrenia were evaluated using Cox proportional-hazards models. Schizophrenia group had comparable macrovascular (adjusted OR 0.99 [95% CI 0.92–1.06]) and lower microvascular (0.79 [0.73–0.86]) complication rates relative to comparison group. Mortality risk ratio for schizophrenia was elevated at all complication burden levels, which conferred incremental impact on excess mortality in both groups. Cardiovascular diseases (1.60 [1.45–1.77]) and cerebrovascular-metabolic diseases (2.74 [1.25–5.99]) were associated with the highest differential mortality in schizophrenia among various specific complications and complication combinations, respectively. Our results indicate that schizophrenia patients with co-existing diabetes are at increased risk of excess mortality relative to those with diabetes alone, regardless of complication burden levels. Implementation of multilevel, targeted interventions is needed to improve diabetes-related outcomes and reduce mortality gap in this vulnerable population.