The burden of mental ill health associated with childhood maltreatment in the UK, using The Health Improvement Network database: a population-based retrospective cohort study

Background
Childhood maltreatment is a global public health, human rights, and moral issue that is associated with a substantial mental health burden. We aimed to assess the association between childhood maltreatment and the development of mental ill health and the initiation of new prescriptions for mental ill health.

Methods
In this population-based, retrospective, open cohort study, we used a dataset from individuals in The Health Improvement Network (THIN) database. THIN database comprises UK electronic medical records taken from 787 general practices throughout the UK. We used read codes in these records to identify exposed patients (those with a read code identifying officially confirmed childhood maltreatment or a maltreatment-related concern) and up to two unexposed patients (those without such read codes) from the same general practice, who were matched by age and sex. We evaluated the risk of developing depression, anxiety, or serious mental illness (a composite mental ill health outcome) or initiation of a prescription drug used to treat mental ill health, and the odds ratio of these events at baseline, in the exposed versus unexposed patients.

Findings
The first possible date for cohort entry (the study start date) was Jan 1, 1995, and patients could enter the cohort until the study end date, Dec 31, 2018. During the study period, 11 831 850 patients were eligible to participate. Of these patients, we identified 217 758 (1·8%) patients with any recorded childhood maltreatment. These patients were matched to 423 410 unexposed control patients with no recorded exposure to childhood maltreatment. The exposed group were followed up for a median of 1·8 years (IQR 0·6–4·3) versus 3·2 years (1·3–6·1) in the unexposed group. During the study period, 11 665 (5·9%) new diagnoses of mental ill health were made in the exposed group, giving an incidence rate of 16·8 events per 1000 person-years versus 15 301 (3·7%) new recorded diagnoses at an incidence rate of 8·3 events per 1000 person-years in the unexposed cohort, giving an adjusted IRR of 2·14 (95% CI 2·08–2·19). 30 911 (14·8%) patients in the exposed group received a new prescription for any type of mental ill health (incidence rate 46·5 events per 1000 person-years) versus 36 390 (8·9%) patients in the unexposed group (20·5 per 1000 person-years) resulting in an adjusted IRR of 2·44 (95% CI 2·40–2·48).

Interpretation
Childhood maltreatment is thought to affect one in three children globally; therefore, a doubled risk of developing mental ill health among these individuals represents a substantial contribution to the mental ill health burden in the UK. It is imperative that public health approaches, including those aimed at preventing and detecting childhood maltreatment and its associated negative consequences, are implemented to prevent mental ill health.