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.

This collaborative, interdisciplinary and innovative project aims to investigate the potential impact of air pollution exposure on clinically diagnosable mental health problems by pioneering a novel linkage of high-resolution multi-location ambient air pollution exposure estimates with a densely phenotyped longitudinal cohort of twins. Expanding on pilot work in London produced as part of an existing collaboration, this project will explore associations between modelled air pollution exposure estimates for a one-year period across multiple locations and several psychiatric disorders at age 18 in a cohort of over 2000 twins spread across the UK.

The quality of our extensive cohort data, the high resolution of the pollution estimates, and the twin design, which enables us to ensure our findings are robust to unmeasured confounders, will guarantee the results of this project substantially improve upon existing research and advance our understanding of the role of air pollution exposure in the aetiology of psychiatric disorders. This will move the field closer to prevention and encourage clinicians and policymakers to develop ways to manage such risks to health.

This project is intended to provide an important exemplar of how environmental data can be successfully combined with large-scale cohort data to improve understanding of the impact of our environment on health and wellbeing. Therefore, we hope this will pave the way for additional innovative integrations of environmental data with the extensive cohort study data available in the UK by demonstrating the feasibility and effectiveness of such interdisciplinary undertakings and draw the attention of different disciplines to such opportunities. To highlight these, the PI and Co-I will write an opinion paper on the importance of combining environmental and health data and discussing the feasibility of implementing this using the experience gained during the proposed study as well as recommending how this approach could be extended and capitalised upon in the future. It is intended that this would be published in Environmental Health Perspectives. We will also write a letter or opinion piece for a medical or psychiatric journal to raise awareness of the usefulness of combining environmental data with cohort and other data (e.g., electronic health records) to increase understanding of mental and physical health outcomes and improve health care. Additionally, the findings of the project will be disseminated via oral presentation at the London Air Quality Network Conference, which attracts academics and policymakers from across the UK and Europe. This will provide an important platform for reaching a wider audience. We will also seek out other opportunities via online and offline media to promote the findings of this project and ignite discussion around the role of air pollution in mental health problems and draw attention to the opportunities that exist to investigate such issues further.

In terms of future impact, the findings obtained from this study would provide an invaluable foundation for a larger grant application to model air (and noise) pollution exposure estimates for a longer period (e.g., 2003-2012) and integrate these with the extensive longitudinal data available for the E-Risk cohort. This has the potential to further increase understanding of the impact of pollution on health, as it would enable us to explore associations between trajectories of pollution exposure with changes in mental health problems over time and ascertain whether the timing of exposure to high concentrations of pollutants (e.g., in childhood vs. adolescence) has an impact on the likelihood of developing a psychiatric disorder. A wider range of health and functional outcomes at age 18 and earlier ages could also be explored, along with the mechanisms underlying such associations, due to the wealth of phenotypic and biobanked data available across development for E-Risk participants.