Comorbid alcohol and mental health disorders: a longitudinal analysis of development to young adulthood

Abstract

Background: Alcohol is the most widely consumed of the psychoactive substances and was responsible in 2012 for nearly 6% of all global deaths. Disorders of alcohol use are highly comorbid with mental health disorders and create a significant health burden: the two are responsible for 183.9 million DALYs annually. The majority of this burden of disease falls on young adults, and despite the poorer prognosis and more frequent relapse that characterise this condition, information on early life factors associated with its development is limited. Data provided by large scale population studies and reports on clinical samples are valuable but are limited by the lack of prospective measures or cannot be generalised due to sample specificity. Although predictors of alcohol use disorders and mental health disorders have separately been widely studied, their application to comorbidity is not straightforward. Aims: This study has three main aims: 1. To describe the prevalence, types and onset of comorbidities of mental health and alcohol use disorders in young Australians; 2. To understand factors from different phases of the life span which may predict the onset of comorbidity or be affected by it, and which may present targets for intervention; and 3. To consider the role of alcohol in the context of illicit substance and mental health comorbidities. In this context, this research program aims to explore factors which may distinguish comorbidity from its constituent disorders. Methods: Data from this study were drawn predominantly from the Mater-University of Queensland Study of Pregnancy (MUSP), a pre-birth linked cohort of mothers and children begun in 1981. The baseline sample of 7223 pregnancies comprising the original cohort was followed for twenty-one years, providing prospective measures of health and related factors for both mother and child. At twenty one years, structured psychiatric interviews of the offspring provided lifetime DSM-IV diagnoses of mental health, alcohol and other substance use disorders. The condition of interest, alcohol and mental health disorders which co-occurred within a 12-month period, was examined in light of important developmental factors ranging from pre-birth to late adolescence, using primarily multinomial logistic regression analyses. Additional data from the Healthy Neighbourhoods Study were analysed to examine potential markers of early-emerging co-occurring conditions in pre-adolescent students. Key findings: Comorbid alcohol and mental health disorders are highly prevalent at young adulthood, occurring in 12% of this representative sample. Indicators of this comorbidity may be detected in children as young as 10-14 years old. A number of factors distinguish the risk of comorbidity from that of single disorders. Socio-economic disadvantage derived from the family of origin contributes significantly to the risk of comorbidity, with risk increasing in a dose-response manner for multiple dimensions of disadvantage. Maternal smoking during pregnancy is also implicated, independent of its socio-economic aspect, as is low mother-child warmth. In pre-adolescent years, co-occurring depressive symptoms and drinking were associated with low school commitment and family substance problems, while good adaptive coping skills were linked to a lower risk of this co-occurrence. During adolescence, child smoking, drinking and attention and/or thought disorders may be seen as early indicators of developing comorbidity. During adulthood, individuals with comorbid disorders are more likely to exhibit behavioural problems, particularly aggression and delinquency, but are also more vulnerable to experiencing psychological or physical forms of interpersonal violence. We also confirm that the antecedents of alcohol/mental health comorbidity differ from illicit substance/mental health comorbidity, and that common mental health disorders are strongly associated with poly-substance use disorders in young adults. Conclusions: This study extends our knowledge of comorbid alcohol use and mental health disorders by characterising the prevalence and the predictors of comorbidity for young adults in the general population. In addition to the health burdens, individuals with comorbid disorders are more likely to exhibit problematic behaviours at youth and adulthood which may leave them vulnerable to engagement with the judicial system. Features of the family environment, starting pre-birth, distinguish comorbid alcohol use and mental health disorders from single disorders and several predictors distinguish this comorbidity from that with illicit substance use disorders. Early identification is possible, and intervention with this group may help reduce the burden on both health and justice systems, but such interventions must also take into consideration the multiple socio-economic disadvantages experienced by this group.