Artificial outdoor light at night and depression in older adults in the USA, England, Northern Ireland, and Ireland

Background

Artificial Light at night (ALAN) is a potential environmental stressor for depression, but epidemiological evidence is limited. Cross-national surveys of aging were leveraged to examine LAN and depression.

Methods

We used longitudinal aging surveys from the US (HRS; n = 20,868), England (ELSA; n = 9848), Ireland (TILDA; n = 6407), and Northern Ireland (NICOLA; n = 2725). Depression was ascertained using Center for Epidemiologic Studies Depression Scale and dichotomized based on study-specific cutoffs. Annual mean outdoor ALAN exposure was estimated using satellite-derived nighttime light data (∼500 m resolution), then categorized using harmonized quartiles, based on cross-country population values (≤2.79, 2.79-11.69, 11.69-23.93 and >23.93 nW/cm2/s). Poisson regression models estimated the prevalence ratios (PRs) of depression, adjusting for individual- and area-level factors.

Results

The prevalence of depression was highest in ELSA and HRS (24%), followed by NICOLA (14%) and lowest in TILDA (8%). The mean (SD) ALAN levels were 18.9 (9.0) nW/cm2/s in HRS, 13.4 (12.7) in ELSA, 10.4 (13.4) in TILDA, and 11.6 (10.3) in NICOLA. In fully-adjusted models, the highest ALAN quartile was associated with higher PRs of depression (reference: lowest quartile), in all surveys, with PRs (95% Confidence interval) of 1.40 (1.20–1.63) in HRS, 1.16 (0.98–1.38) in ELSA, 1.51 (1.08–2.10) in TILDA, and 1.79 (1.13–2.84) in NICOLA. The directions of the association were robust to adjustment for NO2, though attenuated.

Conclusions

Findings from multiple countries suggest that outdoor ALAN exposure is associated with depression in older adults and highlight the value of international longitudinal aging cohorts for investigating the impact of environmental exposures on health.