Increased prevalence of anxiety symptoms modestly associated with poor air quality

1. Greater and more recent exposure to fine particulate matter, was linked with a small increase in anxiety symptom risk.

2. No association was found between anxiety symptom risk and coarse particulate matter or proximity to major roadways.

Evidence Rating Level: 2 (Good)

Study Rundown: The risk of developing mental illness is highly dependent on genetic predispositions and adverse environments. While the presence of fine particulate matter (2.5 micrometers or less, PM_2.5) has already been linked with increased risk of cardiovascular disease, little is still known about the risk of particulate matter exposure and mental illness. This observational cohort study, using data from the Nurses’ Health Study, found an increased risk of anxiety with increased exposure to PM_2.5, but not PM_2.5-10, through a spatiotemporal prediction model. The relative contribution of PM_2.5 to increased anxiety symptom risk was observed at time windows of 1 month to 15 years and was roughly around 10-15% in increased risk. There no change in this correlation when considering age, previous anxiety levels before the study period, proximity to a major roadway, region of the country, presence of co-morbidities including pulmonary and cardiac disease, and high levels of coarse particulate matter.

The results of this study are intriguing and lend support to a growing body of evidence linking systemic inflammation with increased risk of mental illness. However, the small effect size in this study, spatiotemporal prediction as opposed to direct measurement of PM_2.5, and lack of clinical diagnosis of anxiety/depression should warrant a conservative interpretation of these findings, as a mechanistic understanding of this association is far from clear. A future prospective cohort study analyzing anxiety symptoms and PM_2.5 with timed blood draws to measure inflammatory markers in parallel may greatly increase our understanding of this process and help validate this study’s results.

Click to read the study in the BMJ

Click to read an accompanying editorial in the BMJ

Relevant Reading: Effect of long-term outdoor air pollution and noise on cognitive and psychological function in adults

In-Depth [retrospective cohort]: 71,271 women (age 57-85) originally participants of the Nurse’s Health Study in the United States were surveyed to elucidate the relationship between pollution and anxiety. Spatiotemporal predictions of particulate matter pollution were compiled using geographic, meteorological, and nationwide monitor data and prevalence of anxiety symptoms was measured by the Crown-Crisp phobic anxiety scale score (not an official diagnosis of anxiety). The adjusted odds ratios per 10 μg/m3 greater exposure to PM_2.5 and high levels of anxiety symptoms were 1.12 (CI₉₅ 1.06-1.19) for the 1 month time window post exposure, 1.13 (CI₉₅ 1.06-1.21) for 3 months, 1.14 (CI₉₅ 1.05-1.23) for 6 months, 1.15 (CI₉₅ 1.06-1.23) for 12 months, and 1.09 (CI₉₅ 1.01-1.18) for 15 years. There were no changes in these associations when considering age, previous anxiety levels before the study period, proximity to a major roadway, region of the country, presence of co-morbidities including pulmonary and cardiac disease, and high levels of coarse particulate matter, among a comprehensive list of potential confounders. There was no association found between exposure to PM_2.5-10 and high anxiety symptoms.

Image: PD

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