Impact of air pollution on mental illness in early adulthood: Feasibility study combining UK twin cohort data with modelled air pollution exposure

Air pollution is a worldwide environmental health issue. Exposure to high levels of pollution has been linked to a range of physical health problems, including cardiovascular and respiratory illnesses. Recent research suggests that air pollution may also have an effect on mental health. However, these studies suffer from a number of methodological problems which make it difficult to draw any firm conclusions about the relationship between exposure to air pollution and mental health problems. This is important to ascertain as psychiatric disorders, such as depression, place a massive burden on individuals, families and society. If we understand what causes them to develop then we can design effective interventions and introduce policies (such as reducing pollution levels) to prevent them from occurring. Moreover, as the vast majority of all psychiatric disorders have started by early adulthood, it is essential to focus on exposure prior to this period to maximise prevention opportunities. Therefore, this project will capitalise on a unique cohort of over 2000 UK twins from the Environmental Risk (E-Risk) Longitudinal Twin study and link the in-depth clinical assessments completed on them at age 18 with high-resolution estimates of their exposure to air pollution in the previous year to investigate more comprehensively the potential impact of air pollution exposure on mental health problems. Specifically, outdoor concentrations for a range of pollutants will be estimated around the E-Risk participants' residential addresses together with two other locations they report spending the majority of their time at during a one-year period (2012) and these will be averaged to produce an annual estimate across the three locations. These estimates will be securely combined with data on past-year psychiatric diagnoses (anxiety, attention-deficit hyperactivity disorder [ADHD], depression, and conduct disorder) obtained on the participants during clinical interviews at age 18. Associations between the estimated level of pollution exposure and each psychiatric disorder will then be examined. This study builds on a smaller-scale pilot conducted by the project team focused just on twins who lived in the London area, which demonstrated that it was feasible to link such datasets and suggested that estimated levels of air pollution exposure were associated with depression, conduct disorder and ADHD at age 18. Given that pollution levels vary widely across the UK it is important to extend this initial work to the full UK sample. The proposed study will substantially improve upon existing studies in several ways. Firstly, we will use a cutting-edge estimation model that can predict air pollution exposure down to address level, which increases the accuracy of estimated exposure. Secondly, we will use a large well-characterised sample of twin children from across the UK who have been extensively assessed since birth thus enabling us to check that air pollution and psychiatric disorders are not spuriously associated due to other factors (e.g., socio-economic status, smoking, victimisation, physical illnesses). We will also compare the rates of psychiatric disorders in twins where one twin has been exposed to high levels of pollution and the other has been exposed to lower levels (due to living in different areas), which allows us to rule out genetic and environmental factors that we cannot measure directly thus increasing confidence in our findings. Overall, the quality of our densely-phenotyped cohort data, the high resolution of the pollution estimates, and powerful twin design, will guarantee the results of this project substantially advance our understanding of the role of air pollution exposure in the development of psychiatric disorders, thus moving us closer to prevention. We anticipate that this project will pave the way for additional innovative integrations of environmental data with the extensive cohort data available in the UK.