The prevalence of mental disorders is high, with estimates indicating that one in three individuals experiences a mental disorder during their lifetime.1, 2, 3 Additionally, there is robust evidence indicating that mental disorders are associated with premature mortality.3 Many studies on mental disorders report risk ratios such as standardised mortality ratios and mortality rate ratios (MRRs), which are useful for comparing how different types of disorders affect premature mortality and to identify specific causes of death.3 Health metrics can also provide information on the age of death or differential life expectancy associated with mental disorders.4 While previous literature has provided a range of health metrics for people with mental disorders,4, 5, 6 there is a need for a harmonised panel of mortality-related health metrics that includes a comprehensive range of mental disorders.
Life expectancy is a widely used health metric, which is readily understood by experts and non-experts alike, and comparing the difference in average lifespan between people with mental disorders and the general population is an intuitive way to measure premature mortality. The best known metric for premature mortality is years of life lost (YLLs), which is used by the Global Burden of Diseases, Injuries, and Risk Factors Study (GBD).7 When considering deaths attributable to specific causes, YLLs estimate the expected remaining life expectancy from age at death on the basis of an ideal standard life expectancy derived from the lowest age-specific mortality rates in any population in the world greater than 5 million. Other studies have used methods based on remaining life expectancy by applying assumptions related to age of onset of the disorder or age of the cohort for follow-up. For example, an Australian study found the life expectancy gap for all mental disorders to be 15·9 years for men and 12·0 years for women.8 A Danish study found similarly large estimates of reduced life expectancy for people with schizophrenia (18·7 years for men and 16·3 years for women).9 However, these studies assumed that all cases of mental disorders had onset at age 15 years.
Research in context
Evidence before this study
Systematic reviews have consistently shown that people with mental disorders have an increased risk of premature mortality. Traditionally, this evidence has been based on relative risks (eg, mortality rate ratios [MRRs]) or crude estimates of life expectancy that do not incorporate variation in the age of onset of the disorder. Recently, a new method has been introduced to estimate life-years lost (LYLs), a measure that incorporates the precise age of onset of the disorder. A literature review indicates that this method has not been applied to a comprehensive range of mental disorders, nor contextualised with traditional mortality-related measures such as MRRs.
Added value of this study
In this register-based cohort study, we use a variety of mortality-related metrics, presented by age, sex, and cause of death, to investigate mortality associated with different types of mental disorders. Besides MRRs, we report premature mortality based on LYLs. We found that people with mental disorders had higher mortality rates than those without, with the largest difference observed at age 33 years (MRR 7·25, 95% CI 7·06–7·44). When looking at specific types of disorders, being diagnosed with all types was associated with higher mortality rates and shorter life expectancies, both in males and females. The largest reduction in remaining life expectancy after diagnosis was observed for substance use disorders. When examining specific causes of death, we found that men with all types of mental disorder had fewer LYLs associated with neoplasm-related deaths compared with the general population, which indicates that the general population loses more years of life due to neoplasms than do those with mental disorders. This finding relates to the ability of the LYL to accommodate competing causes of death. While those with mental disorders had higher rates of dying from neoplasms, they had even higher rates of mortality from other causes, thus reducing their risk of dying from neoplasms. Finally, through an interactive data visualisation website, we allow fine-grained interrogation of our results.
Implications of all the available evidence
Mental disorders are associated with both increased mortality rates and reduced life expectancy when assessed with LYLs. Our new methods provide more accurate estimates of premature mortality and reveal previously underappreciated features related to competing risks and specific causes of death. Our findings reinforce the need to optimise the coordinated care of general medical conditions in those with mental disorders.
Recent advances in health metrics can now take into account the observed age of onset (or age of first administrative onset) of the disorder of interest.4, 10 The life-years lost (LYLs) method focuses on the observed age at diagnosis, differing in this way from GBD's YLLs, which focus on age at death. By using the age at diagnosis, the LYL method allows quantification of the reduction in life expectancy for any type of disease, and not only those defined as potential causes of death, as in the GBD estimations. With LYLs, it has been estimated that the average life expectancy for people with any mental disorder is 10·2 years shorter for men and 7·3 years shorter for women.4 These findings, and a recent study applying these methods to schizophrenia,11 indicate that past estimates might have overestimated the actual contribution of mental disorders to premature mortality. Another advantage of using the LYL metric is that it allows investigation of the association between particular disorders and premature mortality, regardless of the main underlying cause of death. It also allows the decomposition of the total reduction in life expectancy into specific causes of death. Given that differential life expectancy in people with mental disorders is used as a proxy indicator of the effectiveness of health care, which can influence resource allocation,12 it is essential that valid metrics related to differential life expectancy be available.
The aim of this study was to investigate mortality associated with different types of mental disorders. We used high-quality Danish registers to provide an integrated atlas of different estimates related to premature mortality, which can be interrogated by age, sex, type of mental disorder, and specific cause of death.