Mental health consequences of exposure to air pollution over the life course

The World Health Organisation (WHO) and Organization for Economic Co-operation and Development (OECD) rank air pollution as the main environmental cause of premature death globally and concluded that by reducing air pollution levels countries can alleviate the burden of disease by a net benefit of 108.22 million GB£ annually. These estimates are based on the established associations between long and short-term air pollution exposures and adverse cardiopulmonary morbidity and mortality. Studies conducted globally have now linked traffic-derived air pollution exposures with increased risk of neurodevelopmental disorders in children (Raz et al 2015), depression and anxiety (Braithwaite et al 2019), psychosis (Newbury et al 2019) and neurodegenerative conditions (Chen et al 2017), and potential causal pathways have been suggested (Block et al 2009). These neurological impacts imply significant additional economic and societal costs not currently represented in the WHO and OECD assessments. Yet, despite considerable efforts to improve air quality, the majority of the world's urban populations still breathe air failing to meet the health-based WHO Air Quality Guidelines.

A rigorous methodology to improve the current evidence base is needed: The strength of the findings from these population-based studies are often limited by i) the simplicity of brief mental health and psychiatric screening instruments or proxy measures (e.g. prescription of medication) of mental health and psychiatric disorders; ii) over-simplified exposure estimates and surrogates of air pollution measures (e.g. proximity to major roads); iii) not taking into account interactions of air pollution with area- or individual-level indicators (e.g. communities of low socioeconomic status tend to live close to heavy traffic); iv) failure to measure longitudinal exposures from a range of air pollutants from multiple sources; and v) failure to explore potential pathways and mechanisms that are implicated in the association between air pollution and mental health.

A better understanding is needed of sensitive periods, accumulation and very long-term impacts of air pollution on mental health: There is growing evidence of long-term and very long-term (25+) impacts of air pollution on mortality. However, only a single study has explored these associations with mental health outcomes beyond a 25-year time-period and this related only to schizophrenia (Antonsen et al 2021). Similarly, young people may be particularly susceptible to the harmful effects of air pollution, so it is important to capture early life exposures to pollution and explore longitudinally the associations with mental health across the life-course and examine whether timing and duration of exposure matters.

A better understanding is needed of the long-term socioeconomic inequalities in exposure to air pollution: There is a growing body of global evidence that vulnerable communities are more likely to be exposed to higher air pollution levels which could result in impaired health compared to their more affluent counterparts (Pinault et al 2016). Few studies to date have applied a life course perspective to understand the dynamics of air pollution inequalities and their impacts on health so that public health researchers and policymakers can understand the societal and economic implications in order to intervene.

AIM

To investigate the link between air pollution exposure and a broad range of mental health outcomes over the life-course in multiple UK-based longitudinal birth cohorts (National Survey of Health and Development (NSHD), Environmental Risk (E-Risk) longitudinal twin study) and the potential implications of adverse associations for policy and service provision.