Physical health disparities and severe mental illness: a longitudinal comparative cohort study using hospital data in Northern Ireland

Background: People with severe mental illness (SMI) die prematurely, mostly due to preventable causes.
Objective: To examine multimorbidity and mortality in people living with severe mental illness using linked administrative datasets.
Method: Analysis of linked electronically captured routine hospital administrative data from Northern Ireland (2010-2021). We derived sex-specific age-standardised rates for seven chronic, lifelimiting physical conditions (chronic kidney disease; malignant neoplasms; diabetes mellitus; chronic obstructive pulmonary disease; chronic heart failure; myocardial infarction; and stroke) and used logistic regression to examine the relationship between SMI, sociodemographic indicators, and comorbid conditions; survival models quantified the relationship between all-cause mortality and SMI.
Results: analysis was based on 929,412 hospital patients aged 20 years and over, of whom 10,965 (1.3%) recorded a diagnosis of SMI. Higher likelihoods of an SMI diagnosis were associated with living in socially deprived circumstances, urbanicity. SMI patients were more likely to have more comorbid physical conditions than non-SMI patients, and younger at referral to hospital for each condition, than non-SMI patients. Finally, in fully adjusted models, SMI patients had a two-fold excess all-cause mortality.
Conclusion: Multiple morbidities associated with SMI can drive excess mortality. While SMI patients are younger at referral to treatment for these life-limiting conditions, their relatively premature death suggests that these conditions are also quite advanced. There is a need for a more aggressive approach to improving the physical health of this population.