Air pollution and depression symptoms in middle-aged and older adults in Los Angeles County

Long-term exposure to air pollutants may be harmful to the brain, potentially through inducing oxidative stress or inflammation. Few studies of air pollution and depression have been conducted in the United States where this mental health disorder is prevalent among adults. We investigated associations between ambient air pollutants (O₃, PM_2.5 and NO₂) and depression symptoms in middle-aged and older adults (n = 1496) without cardiovascular disease or cognitive impairment in Los Angeles, California.

Air pollution exposures were assigned to residential addresses using a geographic information system with air quality monitoring data. The Center for Epidemiological Studies-Depression scale (CES-D) assessed depression symptoms at study entry. Carotid artery intima-media thickness (CIMT) was obtained as a measure of subclinical atherosclerosis. Linear and Poisson regression models estimated cross-sectional associations between air pollutants and total CES-D score and suspected clinical depression (CES-D score ≥ 16) adjusting for potential confounders and examined effect modification by CIMT.

Higher exposure to O₃, PM_2.5 and NO₂ overall were not cross-sectionally associated with higher CES-D total scores or CES-D score ≥ 16. However, the interaction between CIMT and PM_2.5 was statistically significant (β-interaction term = 1.01, 95% CI = 0.05, 1.97; p-value = 0.03). Adults with CIMT levels ≥ 0.77 mm had higher depression symptom prevalence as PM_2.5 increased (β = 0.04 per 10 µg/m³, 95% CI = -0.22, 0.30) while those with CIMT < 0.77 mm had lower prevalence (β = -0.18, 95% CI = -0.41, 0.05).

Higher O₃, PM_2.5 and NO₂ exposures were generally unassociated with depressive symptoms. Additional studies are needed to investigate whether persons with higher subclinical atherosclerosis are more susceptible to possible PM_2.5 effects on mental health.