Background Major mental illness has previously been identified as a risk factor for ischaemic heart disease (IHD) and stroke. It is not clear whether these associations differ by age, sex, socio-economic status or time period.
Methods Dynamic cohorts of people with no history of hospital admission for IHD or stroke and either a record of hospital admission for schizophrenia or bipolar disorder or no history of hospital admission for severe mental illness were created using Scottish population-based national records. Absolute incidence rates were calculated for all three cohorts and Poisson regression models were used to estimate relative risks (RR) for IHD and stroke events identified using hospital admission and mortality records), stratified by or adjusted for age, sex, time period and area-based deprivation index.
Results Between 1991 and 2015, the absolute risk of IHD and stroke decreased in people with schizophrenia and bipolar disorder and in those without mental illness, but there was little change in the relative risk, comparing those with and without mental illness. IHD risk was about two-fold and 60% higher in people with schizophrenia and bipolar disorder, respectively, compared to those without mental illness (age, sex and deprivation-adjusted RR for schizophrenia in 1991: RR 1.90, 95% CI 1.38, 2.58; and in 2015: RR 2.11, 1.63, 2.74); adjusted RR for bipolar disorder in 1991: RR 1.58, 95% CI 1.48, 1.69; and in 2015: RR 1.64, 1.52, 1.78). Similar results were observed for stroke incidence. RRs were similar across age groups. However, there was an interaction with sex (higher RRs for women than men) and with deprivation (higher RRs in more deprived groups in people with schizophrenia and bipolar disorder than in those without mental illness).
Conclusion History of hospital admissions with schizophrenia or bipolar disorder is associated with higher incidence of IHD and stroke, with stronger associations: in women than men; and in more than less deprived populations, but no evidence of interaction with age and no change in RRs over time.
Better prevention of IHD and stroke is needed in people with major mental illness. Strengths lie in the use of national routine datasets, which provide sufficient power for the study of relatively rare mental health disorders and allow analysis of time trends. The work is however limited use of hospital admission data to define mental illness and the absence of risk factor data.
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