The influence of personality disorder on the future mental health and social adjustment of young adults: a population-based, longitudinal cohort study.

BACKGROUND

Existing knowledge about the consequences of personality disorders is substantially derived from the study of clinical populations. To gain a fuller understanding of the disease burden associated with personality disorders, we report their long-term mental health and social consequences in a large population-based sample of young adults.

METHODS

We used data from a population-based, ten-wave cohort study of a stratified random sample of non-treatment-seeking young adults recruited from Victoria, Australia, between Aug 20, 1992, and March 3, 2014. The population sample was originally recruited in adolescence: here we report the analysis of data collected from wave 8 (participants aged 24-25 years) and wave 10 (participants aged 34-35 years). Presence and severity of personality disorder were assessed at age 24 years with a semi-structured, informant-based interview (the Standardised Assessment of Personality). At age 35 years, participants were assessed on the occurrence of the following outcomes: major depressive disorder, anxiety disorder, smoking and alcohol consumption, illicit substance use, ever having separated from a long-term partner or been divorced, not currently in a relationship, not currently in paid employment, and in receipt of government welfare. We used multiple imputation to address potentially biased estimates resulting from the reduction of the analysis sample to participants who had completed both survey waves. The imputation dataset contained 1635 individuals.

FINDINGS

For the 1520 participants in wave 8, 1145 (75%) informant interviews for personality disorder in these participants took place. At age 24 years, 305 (27%) of the observed sample had either personality difficulties or personality disorder. At age 24 years, in the imputed analysis sample, the severity of personality disorder was associated with the absence of a degree or vocational qualification (adjusted odds ratio [aOR] for the effect of complex and severe personality disorder vs no personality disorder 1·76, 95% CI 1·11-2·76), receipt of welfare (2·52, 1·33-4·78), the presence of common mental disorders (1·77, 1·08-2·90), and cigarette smoking (2·01, 1·29-3·14). At age 35 years, severity of personality disorder was independently associated with not being in a relationship (aOR for the effect of complex and severe personality disorder vs no personality disorder or personality difficulty 2·05, 95% CI 1·21-3·45), increased odds of an anxiety disorder (2·27, 1·2-4·28), and major depression (2·23, 1·24-4·01).

INTERPRETATION

The presence of personality disorder predicts the occurrence of later anxiety and depression, as well as the absence of long-term relationships, effects that are not attributable to pre-existing mental health, substance use or social problems. Our study provides strong support for including personality disorder in global studies of the burden of mental disorders to improve the understanding of population mental health.

FUNDING

Australia's National Health and Medical Research Council (NHMRC) and Victoria's Operational Infrastructure Support Program.