BACKGROUND: Artificial light at night (ALAN) may be an anthropogenic stressor for mental health disturbing humans' natural day-night cycle. However, the few existing studies used satellite-based measures of radiances for outdoor ALAN exposure assessments, which were possibly confounded by traffic-related air pollutants.
OBJECTIVES: To assess 1) whether living in areas with increased exposure to outdoor ALAN is associated with depressive symptoms; and 2) to assess the potential confounding effects of air pollution.
METHODS: We used cross-sectional data from people (N = 10,482) aged 18-65 years in the Netherlands. Depressive symptoms were assessed with the Patient Health Questionnaire (PHQ-9). Satellite-measured annual ALAN were taken from the Visible Infrared Imaging Radiometer Suite. ALAN exposures were assessed at people's home address within 100 and 600 m buffers. We used generalized (geo)additive models to quantify associations between PHQ-9 scores and quintiles of ALAN adjusting for several potential confounders including PMand NO. 2.5 2
RESULTS: Unadjusted estimates for the 100 m buffers showed that people in the 2to 5ALAN quintile showed significantly higher PHQ-9 scores than those in the lowest ALAN quintile (β = 0.503 [95% confidence intervals (CI): 0.207-0.798], β = 0.587 [95% CI: 0.291-0.884], β = 0.921 [95% CI: 0.623-1.218], β = 1.322 [95% CI: 1.023-1.620]). ALAN risk estimates adjusted for individual and area-level confounders (i.e., PM, urbanicity, noise, land-use diversity, greenness, deprivation, and social fragmentation) were attenuated but remained significant for the 100 m buffer (β = 0.420 [95% CI: 0.125-0.715], β = 0.383 [95% CI: 0.071-0.696], β = 0.513 [95% CI: 0.177-0.850], β = 0.541 [95% CI: 0.141-0.941]). When adjusting for NOper 100 m buffers, the air pollutant was associated with PHQ-9 scores, but ALAN did not display an exposure-response relationship. ALAN associations were insignificant for 600 m buffers. nd th Q2Q3Q4Q5 2.5Q2Q3Q4Q5 2
CONCLUSION: Accounting for NOexposure suggested that air pollution rather than outdoor ALAN correlated with depressive symptoms. Future evaluations of health effects from ALAN should consider potential confounding by traffic-related exposures (i.e., NO). 2 2
