P016 Daytime light exposure predicts better mood-, sleep- and circadian-related outcomes in >8,000 UK Biobank participants

INTRODUCTION: Light has powerful effects on mood, sleep, and the circadian system. Humans evolved in an environment with a clear distinction between day and night, but our modern lighting environments have blurred this distinction. While the disruptive effects of night time light exposure are well described, the potential positive effects of daytime light exposure on these systems are less well studied. METHOD: Participants were a subset of the UK Biobank cohort who were invited to complete a seven day wrist-worn actimetry and light sensor study (n = 8,372, 61% female, age range: 39–70). Hierarchical linear models assessed the association between average daytime light exposure and mood-, sleep- and circadian-related outcomes, adjusted for age, sex, and season of assessment. RESULTS: Greater daytime light exposure was associated with earlier chronotype (p < .001), greater ease of getting up in the morning (p < .001), lower odds of using antidepressant medication (p < .001), less frequent low-mood (p = .002), less frequent anhedonia (p < .001), greater happiness (p < .001), less frequent insomnia symptoms (p = .01) and less frequent tiredness (p < .001). CONCLUSIONS: In the largest study to-date, we observe that greater daytime light predicts better outcomes across a range of mood-, sleep- and circadian-related measures. Our findings are consistent with the known effects of light on the circadian system, whereby greater daytime light enhances the strength of the rhythm allowing for greater distinction between sleep and wake states. These findings