Mental health conditions are associated with increased risk of subsequent self-harm, assault and unintentional injuries in two nations

Abstract

Mental health conditions are associated with an increased risk of chronic physical diseases, but their implications for other physical health outcomes, including injuries, are less established. In this prospective cohort study, we tested whether mental health conditions antedate unintentional as well as self-harm and assault injuries, using administrative data from Norway (N = 2,753,646) and New Zealand (N = 2,238,813). In Norway, after accounting for pre-existing injuries, individuals with a primary care encounter for a mental health condition had an elevated risk of subsequent primary care-recorded injury. In New Zealand, as expected, individuals with a mental health-related inpatient hospital admission had an elevated risk of subsequent inpatient hospital-recorded self-harm injury, as well as assault injury. However, they also had an elevated risk of unintentional injuries. Associations extended to injury insurance claims. Associations were evident across mental health conditions, sex, age and after accounting for indicators of socioeconomic status. Risk was particularly increased for brain and head injuries. Patients with mental health conditions are an important group for injury prevention.

Keywords: Epidemiology; Psychiatric disorders; Public health; Risk factors.

Fig. 1. Monthly risk of primary care-recorded injuries among individuals subsequent to presenting to primary care for a mental health condition.

The data are from the Norwegian study population, N = 2,753,646. a, The absolute injury risk for individuals with a mental health condition compared to individuals without a mental health condition. Estimates in a indicate monthly risk of injury. Inverse probability weights were used to balance mental health groups according to age at baseline, sex, county of residence and educational attainment. b, Differences in observed risk of injury events between the groups in a. The 95% CIs for risk differences in b are not shown as they are very narrow; the intervals are presented in Supplementary Table 1. NOS, not otherwise specified.

Fig. 2. Associations of mental health conditions with risk of subsequent injuries in primary care records.

The data are from the Norwegian study population, N = 2,753,646. a, HRs for associations of any mental health condition, and specific types of mental health conditions, with risk of any subsequent injury. b, HRs for associations of any mental health condition, and specific types of mental health conditions, with risk of subsequent injury in specific body systems. Each body system is denoted in a different color. Inverse probability weights were used to balance mental health groups according to age at baseline, sex, county of residence and educational attainment. Models controlled for whether individuals had an injury encounter before their encounter for a mental health condition. Bars indicate 95% CIs.

Fig. 3. Heat map for associations of mental health conditions with subsequent injuries to different body regions in inpatient hospital records.

The data are from the NZIDI study population, N = 2,238,813. We classified injuries according to body region using the Barell matrix^,. Injuries from self-harm were excluded. Models controlled for birth year, sex and whether individuals had an injury admission before their first admission for a mental health condition. Estimates are risk ratios (RR); 95% CIs are reported in the main text.

Extended Data Fig. 1. Study population selection process.

This figure shows the selection processes for the Norwegian (A) and New Zealand (B) study populations.