Increased risk for depression and anxiety may stem from long-term exposure to multiple air pollutants at low concentrations, according to study findings published in the Journal of the American Medical Association Psychiatry.
Investigators sought to assess the association between long-term joint exposure to multiple air pollutants and incident depression and anxiety.
They conducted an analysis of data in the UK Biobank, a population-based prospective study that recruited participants from March 2006 through September 2010. The current analysis included 389,185 participants (mean age, 56.7±8.1 years; 52.9% women) of whom 13,131 developed depression and 15,835 developed anxiety during the median follow-up of 10.9 years (IQR, 10.1-11.6 years).
Incidence of depression and anxiety were identified by ICD-10 codes. Investigators used the main air pollutants in the UK to generate an air pollution score to assess joint exposure to multiple air pollutants. They used Cox proportional hazard models to estimate the hazard ratios (HRs) for the associations of individual air pollutants and air pollution score in quartiles with incidence of depression and anxiety. Among all participants (94.4% White), those with depression or anxiety diagnosed at baseline were excluded along with participants with missing information of air pollution exposure in the main analysis.
Exposures included annual mean air pollution concentrations of particulate matter (PM) with aerodynamic diameter of 2.5 μm or less (PM2.5) and PM with aerodynamic diameter between 2.5 μm and 10 μm (PM2.5-10). For each participant’s residential address, estimates of nitrogen dioxide (NO2) and nitric oxide (NO) were determined using a land use regression model (31% of participants lived in the same residence <10 years; 59% of participants were actively employed).
Investigators noted the median concentration of pollutants was PM2.5, 9.9 (IQR, 9.3-10.6) μg/m3; PM2.5-10, 6.1 (IQR, 5.8-6.6) μg/m3; NO2, 26.0 (IQR, 21.3-31.1)μg/m3; and NO, 15.9 (IQR, 11.6-20.6)μg/m3, (below annual values for PM2.5 and NO2 in UK air quality standards).
According to investigators, estimated long-term exposure to multiple air pollutants was associated with an increased risk for depression and anxiety. They noted the exposure-response curves were nonlinear (with plateauing trends at higher exposure and steeper slopes at lower concentrations). This suggests the risk of incident depression and anxiety tended to be steeper at lower air pollution levels and plateauing at higher exposures. They compared the highest quartile of air pollution score with the lowest quartile for depression (hazard ratio [HR], 1.16; 95% CI, 1.09-1.23; P <.001) and anxiety (HR, 1.11; 95% CI, 1.05-1.17; P <.001).
Quartiles 2 and 3 compared with the lowest quartile of the air pollution score for depression (HR, 1.08; 95% CI, 1.02-1.14; P =.004), and (HR, 1.17; 95% CI, 1.11-1.24; P <.001), respectively. Quartiles 2 and 3 compared with the lowest quartile of the air pollution score for anxiety (HR, 1.09; 95% CI, 1.04-1.14; P <.001), and (HR, 1.14; 95% CI, 1.08-1.19; P <.001), respectively. Similar trends were found for PM2.5, NO2, and NO.
Investigators noted men had a higher association between PM2.5 and anxiety than women (HRmen, 1.18; 95% CI, 1.08-1.29; HRwomen, 1.07; 95% CI, 1.00-1.14; P =.009) in a subgroup analysis.
Significant study limitations include unaccounted-for additional air pollutants (ozone, sulfur dioxide, carbon monoxide), air pollution at baseline may not reflect air pollution trends during follow-up, possible selection bias in the UK Biobank due to nonresponse of potential participants, residual confounding, participants with depression or anxiety not diagnosed during follow-up, preponderance of White participants limiting generalizability, and the possible existence of reverse causality.
“Study results suggest that estimates of long-term exposure to multiple air pollutants was associated with increased risk of depression and anxiety,” investigators concluded. They wrote, “Reductions in joint exposure to multiple air pollutants may alleviate the disease burden of depression and anxiety.” With air quality in many countries well above World Health Organization global air quality guidelines 2021, investigators urge stricter standards for air pollution control.
Yang T, Wang J, Huang J, Kelly FJ, Li G. Long-term exposure to multiple ambient air pollutants and association with incident depression and anxiety. JAMA Psychiatry. Published online February 1, 2023. doi:10.1001/jamapsychiatry.2022.4812