According to a prospective, population-based cohort study recently published in the Journal of the American Medical Association of Psychiatry, long-term exposure to multiple air pollutants, even at low concentrations, increases the risk of depression and anxiety.

Previous research indicated that air pollution is now recognized as an important environmental risk factor for developing mental health issues; however, epidemiologic evidence on long-term exposure to low levels of air pollutants with incident depression and anxiety is still minimal.

As a result, researchers aimed to examine the correlation between long-term joint exposure to multiple air pollutants and the prevalence of depression and anxiety.

The researchers employed data from the UK Biobank, a population-based prospective cohort study that recruited participants from March 2006 through September 2010 and included individuals who had never been diagnosed with depression or anxiety at baseline and had full information on exposure and covariates. Data were examined from May 1, 2022, to October 10, 2022.

The current analysis was comprised of 389,185 participants (average age, 56.7 ± 8.1 years; 52.9% women), of whom 13,131 developed depression and 15,835 developed anxiety during the average follow-up of 10.9 years (interquartile range [IQR] 10.1-11.6 years).

Exposures included annual mean air pollution concentrations of particulate matter (PM) with an aerodynamic diameter of 2.5 micrometers or less (PM2.5) and PM with an aerodynamic diameter between 2.5 micrometers and 10 micrometers (PM2.5-10).

For each participant’s residential address, estimates of nitrogen dioxide (NO2) and nitric oxide (NO) were ascertained employing a land-use regression model (31% of participants lived in the same residence <10 years; 59% of participants were actively employed).

The researchers used the primary air pollutants in the UK to generate an air pollution score to measure joint exposure to multiple air pollutants. They employed Cox proportional hazard models to estimate the hazard ratios (HRs) for the associations of individual air pollutants and air pollution scores in quartiles with the incidence of depression and anxiety. Using ICD-10 codes, the incidence of depression and anxiety was identified.

Among all participants (94.4% Caucasian), those with depression or anxiety diagnosed at baseline were excluded, along with participants with missing information of air pollution exposure in the primary analysis.

During a median (IQR) follow-up of 10.9 years, among 389,185 participants, a total of 13,131 and 15,835 patients were diagnosed with depression and anxiety, respectively. The exposure-response curves were nonlinear, with steeper slopes at lower concentrations and plateauing trends at greater exposure. Moreover, long-term estimated exposure to multiple air pollutants was correlated with heightened risk of depression and anxiety.

The hazard ratios (HRs) and 95% CIs for depression and anxiety were 1.16 (95% CI; 1.09-1.23, P <.001) and 1.11 (95% CI; 1.05-1.17, P <.001) in the highest quartile compared with the lowest quartile of air pollution score, respectively. Comparable trends were shown for PM2.5, NO2, and NO.

The researchers also noted that among men, there was a higher correlation between PM2.5 and anxiety when compared with women (HR men, 1.18; 95% CI, 1.08-1.29; HR women, 1.07; 95% CI, 1.00-1.14; P = .009) in a subgroup analysis.

They discovered that individuals in the highest quartile of exposure were 11% more likely to experience anxiety than those in the lowest quartile. Furthermore, those with higher exposure were approximately 16% more likely to experience depression than those with lower exposure.

The authors concluded that their findings imply that the assessments of long-term exposure to multiple air pollutants were correlated with heightened risk of depression and anxiety.

The authors wrote, “The nonlinear associations may have important implications for policymaking in air pollution control. Reductions in joint exposure to multiple air pollutants may alleviate the disease burden of depression and anxiety.”

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