Long-term exposure to PM air pollution and mental health: a retrospective cohort study in Ireland.

Background: Mental illness is the leading cause of years lived with disability, and the global disease burden of mental ill-health has increased substantially in the last number of decades. There is now increasing evidence that environmental conditions, and in particular poor air quality, may be associated with mental health and wellbeing.

Methods: This cross-sectional analysis uses data on mental health and wellbeing from The Irish Longitudinal Study on Ageing (TILDA), a nationally representative survey of the population aged 50+ in Ireland. Annual average PM concentrations at respondents' residential addresses over the period 1998-2014 are used to measure long-term exposure to ambient PM.

Results: We find evidence of associations between long-term exposure to ambient PM and depression and anxiety. The measured associations are strong, and are comparable with effect sizes for variables such as sex. Effects are also evident at relatively low concentrations by international standards. However, we find no evidence of associations between long-term ambient particulate pollution and other indicators of mental health and well-being such as stress, worry and quality of life.

Conclusions: The measured associations are strong, particularly considering the relatively low PM concentrations prevailing in Ireland compared to many other countries. While it is estimated that over 90 per cent of the world's population lives in areas with annual mean PM concentrations greater than 10 μg/m, these results contribute to the increasing evidence that suggests that harmful effects can be detected at even low levels of air pollution.