BackgroundThe detrimental effects of exposure to light at night (LAN) have received increasing attention. However, the effects of LAN exposure on depressive symptoms and underlying mechanism are less explored. ObjectivesTo investigate the association between LAN exposure with new-onset and trajectories of depressive symptoms, and the potential mediating role of systemic inflammation. MethodsBaseline bedroom LAN exposure was monitored every minute for 2 consecutive nights using a portable illuminance meter. Fasting blood samples were collected at the 1-year follow-up to determine high sensitivity C-reactive protein (hs-CRP). Depressive symptoms were assessed at baseline, 1- and 2-year follow-up using the Mood and Feelings Questionnaire (MFQ). ResultsAt baseline, the mean age of the 347 participants was 18.7 ± 0.8 years, and 35.2 % were men. At 2-year follow-up, the new-onset depressive symptoms were 14.7 %. Compared with low-LANavg (average light intensity from bedtime to rising time) intensity group (LANavg < 3 lx), those with high-LANavg intensity (LANavg ≥ 3 lx) were associated with an 125 % increase in risk for depressive symptoms (HR = 2.25; 95 % CI: 1.27, 4.00); Compared with short-LAN5 (duration of nighttime light intensity ≥5 lx) duration group (LAN5 < 45 min), those with long-LAN5 duration (LAN5 ≥ 45 min) were associated with an 119 % increase in risk for depressive symptoms (HR = 2.19; 95 % CI: 1.18, 4.06). Participants were classified into 3 trajectory groups: consistently low, slow or rapid increase depressive symptoms; both intensity and duration of LAN exposure were associated with higher likelihood of slow or rapid increase depressive symptoms. Additionally, hs-CRP partially mediated the relationship between intensity (mediation proportion: 7.1 %) and duration (mediation proportion: 10.6 %) of LAN exposure with depressive symptoms. ConclusionExcessive bedroom LAN exposure is associated with increased risk of depressive symptoms among young adults, and systemic inflammation may be a partial mediator in the LAN-depressive symptoms association.
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