Trends in standardized mortality among individuals with schizophrenia, 1993-2012: a population-based, repeated cross-sectional study

Abstract

Background: We examined mortality time trends and premature mortality among individuals with and without schizophrenia over a 20-year period.

Methods: In this population-based, repeated cross-sectional study, we identified all individual deaths that occurred in Ontario between 1993 and 2012 in persons aged 15 and over. We plotted overall and cause-specific age- and sex-standardized mortality rates (ASMRs), stratified all-cause ASMR trends by sociodemographic characteristics, and analyzed premature mortality using years of potential life lost. Additionally, we calculated mortality rate ratios (MRRs) using negative binomial regression with adjustment for age, sex, income, rurality and year of death.

Results: We identified 31 349 deaths among persons with schizophrenia, and 1 589 902 deaths among those without schizophrenia. Mortality rates among people with schizophrenia were 3 times higher than among those without schizophrenia (adjusted MRR 3.12, 95% confidence interval 3.06-3.17). All-cause ASMRs in both groups declined in parallel over the study period, by about 35%, and were higher for men, for those with low income and for rural dwellers. The absolute ASMR difference also declined throughout the study period (from 16.15 to 10.49 deaths per 1000 persons). Cause-specific ASMRs were greater among those with schizophrenia, with circulatory conditions accounting for most deaths between 1993 and 2012, whereas neoplasms became the leading cause of death for those without schizophrenia after 2005. Individuals with schizophrenia also died, on average, 8 years younger than those without schizophrenia, losing more potential years of life.

Interpretation: Although mortality rates among people with schizophrenia have declined over the past 2 decades, specialized approaches may be required to close the persistent 3-fold relative mortality gap with the general population.

Conflict of interest statement

Competing interests: None declared.

© 2017 Canadian Medical Association or its licensors.

Figures

Figure 1:

Temporal trends in all-cause age- and sex-standardized mortality rates in individuals with and without schizophrenia (SCZ) overall, by sex, by income quintile (where Q1 = lowest and Q5 = highest) and by rural or urban residence. Trends were examined using unadjusted linear regression models, and significant (p < 0.05) trends between 1993 and 2012 are indicated by an asterisk. Delta (δ) values indicate the relative differences between 1993 and 2012 rates, expressed as a percentage of the 1993 rate; for absolute differences, see Appendix 2, available at www.cmaj.ca/lookup/suppl/doi:10.1503/cmaj.161351/-/DC1). Mortality rates were age- and sex-standardized to the 2006 Ontario population using the direct method. For each trend line, the 1993 and 2012 data points are noted explicitly within the graph.

Figure 2:

Temporal trends in cause-specific (natural and unnatural) age- and sex-standardized mortality rates in individuals with and without schizophrenia. Trends were examined using unadjusted linear regression models, and significant (p < 0.05) trends between 1993 and 2012 are indicated by an asterisk. Delta (δ) values indicate the relative differences between 1993 and 2012 rates, expressed as a percentage of the 1993 rate; for annual rates and absolute differences, see Tables 3 and 4. Accidental causes of death include motor vehicle crashes, inadvertent poisoning, falls, fire, and drugs or adverse events in therapeutic use. Metabolic causes include metabolic, nutritional, immunity and endocrine conditions, as well as diseases of the digestive system. Mortality rates were age-and sex-standardized to the 2006 Ontario population using the direct method.