Daily light-dark exposure patterns and depressive symptoms in U.S. adults: Findings from NHANES 2011–2014

To investigate the associations of objectively measured daytime and nighttime ambient light exposure with depressive symptoms in U.S. adults to explore whether selected liver-related biomarkers statistically accounted for part of these associations. We conducted a cross-sectional analysis of 7,556 adults from NHANES 2011–2014. Ambient illuminance was measured in lux using wrist-worn ActiGraph GT3X+ devices. Daytime (07:30–19:30) and nighttime (00:00–05:30) windows were defined from the population-level 24-h light profile. Depressive outcomes were assessed using the Patient Health Questionnaire-9 (PHQ-9) and analyzed as probable depression (PHQ-9≥10) and as a continuous score. Multivariable logistic and linear regression models were used to estimate associations, and interaction terms were examined for effect modification. Exploratory mediation analyses evaluated alkaline phosphatase (ALP), alanine aminotransferase (ALT), aspartate aminotransferase (AST), and gamma-glutamyl transferase (GGT). Compared with participants in the lowest quartile, those in the highest quartile of daytime light exposure were associated with lower odds of probable depression (OR = 0.67, 95%CI: 0.52–0.86) and lower PHQ-9 scores (β = -0.58, 95%CI = −0.86 −0.30). Conversely, the highest quartile of nighttime light exposure was associated with higher odds of probable depression (OR = 1.44, 95%CI: 1.14–1.83) and higher PHQ-9 scores (β = 0.60, 95%CI: 0.32–0.88). Age modified the association between daytime light exposure and probable depression, with a stronger inverse association among adults aged>50 y (nominal P interaction = 0.002; FDR-adjusted p = 0.016). Exploratory analyses identified small potential indirect pathways through ALP and GGT for daytime light exposure. Brighter daytime light exposure was associated with lower odds of probable depression and lower PHQ-9 scores, whereas brighter nighttime light exposure showed the opposite pattern. The daytime association was stronger among adults aged > 50 y. Exploratory analyses suggested small potential indirect pathways through ALP and GGT, but prospective studies are needed to establish temporality and underlying mechanisms.