Air pollution ups depression and anxiety risks

Long-term exposure to low levels of multiple air pollutants is associated with increased risks of depression and anxiety, a population-based study has shown.

Air pollution has been increasingly recognized as an important environmental risk factor for mental disorders, but all previous studies were conducted in highly polluted countries (ie, Korea and China). “Epidemiologic evidence on long-term exposure to low levels of air pollutants [and its association] with incident depression and anxiety is still very limited,” wrote the researchers. [JAMA Psychiatry 2023;doi:10.1001/jamapsychiatry.2022.4812; www.iqair.com/world-most-polluted-countries]

Using data from the UK biobank, 389,185 individuals who had not been diagnosed with depression or anxiety (mean age, 56.7 years, female, 52.9 percent) were recruited from 13 March 2006 to 1 October 2010. Data were analyzed between 1 May 2022 and 10 October 2022.

Annual concentrations of air pollutants were estimated for each participant’s residential address using the land use regression model, with median concentrations as follows: particulate matter with aerodynamic diameter ≤2.5 µm (PM_2.5), 9.9 µg/m³; PM_2.5-10, 6.1 µg/m³; nitrogen dioxides (NO₂), 26.0 µg/m³; nitrogen oxide (NO), 15.9 µg/m³. Joint exposure to these air pollutants was used to construct an air pollution score.

During a median follow-up of 10.9 years, 13,131 and 15,835 individuals were diagnosed with depression and anxiety, respectively, translating into an incidence of 0.32 cases per 100 person-years and 0.39 cases per 100 person-years, respectively.

Long-term exposure to low levels of multiple air pollutants was found to be associated with increased risks of depression and anxiety, even at concentrations below the UK air quality standards. “Air pollution exposure may affect the central nervous system by inflammatory and oxidative stress pathways through olfactory receptor neurons, the trigeminal nerve, or the systemic circulation, [which] may contribute to the onset of depression and anxiety,” explained the researchers.

“The exposure-response curves were nonlinear, with steeper slopes at lower levels and plateauing trends at higher exposure,” reported the authors. Compared with the lowest quartile of the air pollution score, higher quartiles were associated with elevated risks of depression (quartile 2: hazard ratio [HR], 1.08; quartile 3: HR, 1.17; quartile 4: HR, 1.16) and anxiety (quartile 2: HR, 1.09; quartile 3: HR, 1.14; quartile 4: HR, 1.11). Similar trends were shown for PM_2.5, NO₂, and NO.

Subgroup analysis showed a tendency for stronger association between anxiety and PM_2.5 in male vs female individuals (quartile 4: male individuals, HR, 1.18; female individuals, HR, 1.07; p=0.009), indicating that gender may play a role in modulating susceptibility to anxiety and PM_2.5 exposure. “Oestrogen fluctuation in female individuals and differences in the hypothalamic-pituitary-adrenal [HPA] axis between male and female individuals may play a role in the associations,” added the researchers.