Strengths and limitations
A major strength of this study was the ability to examine the link
between mental disorders and accidental death in the largest
cohort to date using registry data for an entire national
population. Mental disorders were ascertained using out-patient
as well as in-patient diagnoses from all healthcare settings
nationwide, enabling more reliable risk estimates than studies
limited to hospitalised cases or selected samples. The results were
adjusted for broadly measured confounders, and we assessed the
mediating effect of comorbid substance use.
Limitations included the inability to examine mental disorders
that were undiagnosed, thus mental disorders in this study likely
underestimated the true prevalence in the population. This has
an uncertain effect on risk estimates but may cause attenuation
towards the null hypothesis by making the two groups (those with
and without mental disorders) spuriously more similar with
respect to the outcome. Regardless, because we used nationwide
out-patient and in-patient data in Sweden, which has universal
healthcare access, ascertainment was much more complete than
in previous studies. Substance use disorders also were ascertained
using nationwide out-patient and in-patient diagnoses, which
likely underestimated their true prevalence and influence as
mediators. Some suicides may have been misclassified as
accidental deaths,30,31 despite the exclusion of ‘deaths of
undetermined intent’ from the study outcomes. Suicide is a
stigmatising and distressing verdict for families and there can be
pressure to attribute deaths to accidents rather than suicides.
However, the increasing accidental death risk by increasing age
was in contrast to the absence of an age-effect for suicide risk
that we previously noted in this population,23 suggesting that
misclassification was unlikely to be a major influence. Information
on non-fatal accidents was unavailable and would be useful to
examine in future studies when feasible. Finally, some analyses
of specific types of accidents had limited precision because of
small numbers of deaths. Additional large cohort studies will be
needed to further elucidate the risks and mechanisms for different
types of accidents.
Implications
This large national cohort study found that all mental disorders
were strong risk factors for accidental death, which appeared to
be substantially more common than suicide. Mental disorders
were strongly associated with accidental death among adults of
all ages and socioeconomic status, and this was not fully
explained by comorbid substance use. These findings suggest that
interventions to reduce premature mortality among people with
mental disorders should address common underlying
determinants of accidental death in addition to suicide. Improved
awareness of accidental death risks is needed for more effective
overall risk assessment and management.