Angus C Burns1, Richa Saxena2, Céline Vetter3, Andrew J K Phillips1, Jacqueline M Lane2, Sean W Cain4. 1. School of Psychological Sciences and Turner Institute for Brain and Mental Health, Monash University, Melbourne, VIC, Australia. 2. Department of Anesthesia, Critical Care, and Pain Medicine, Massachusetts General Hospital, Boston, MA USA; Medical and Population Genetics, Broad Institute, Cambridge, MA USA; The Division of Sleep and Circadian Disorders, Brigham and Women's Hospital, Boston, MA USA. 3. Department of Integrative Physiology, University of Colorado Boulder, Boulder, CO, USA. 4. School of Psychological Sciences and Turner Institute for Brain and Mental Health, Monash University, Melbourne, VIC, Australia. Electronic address: sean.cain@monash.edu.
Abstract
BACKGROUND: 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 environments have blurred this distinction. Negative effects of light exposure at night have been well characterized. The importance of daytime light exposure has been less well characterized. Here we examine the cross-sectional and longitudinal associations of time spent in daytime outdoor light with mood, sleep, and circadian-related outcomes. METHODS: Participants were drawn from the UK Biobank cohort, a large study of UK adults (n = 502,000; 37-73 years old; 54% women). RESULTS: UK Biobank participants reported spending a median of 2.5 daylight hours (IQR = 1.5-3.5 h) outdoors per day. Each additional hour spent outdoors during the day was associated with lower odds of lifetime major depressive disorder (95% CI OR:0.92-0.98), antidepressant usage (OR:0.92-0.98), less frequent anhedonia (OR:0.93-0.96) and low mood (OR:0.87-0.90), greater happiness (OR:1.41-1.48) and lower neuroticism (incident rate ratio, IRR:0.95-0.96), independent of demographic, lifestyle, and employment covariates. In addition, each hour of daytime light was associated with greater ease of getting up (OR:1.46-1.49), less frequent tiredness (OR:0.80-0.82), fewer insomnia symptoms (OR:0.94-0.97), and earlier chronotype (adjusted odds ratio; OR:0.75-0.77). Auto-Regressive Cross-Lagged (ARCL) models were used to examine the longitudinal association of time spent in outdoor light at baseline with later mood-, sleep- and circadian-related outcomes reported at time point 2. Overall, longitudinal associations support cross-sectional findings, though generally with smaller effect sizes. LIMITATIONS: Future studies that examine the intensity of daytime light exposure at the ocular level are needed. CONCLUSIONS: Our findings suggest that low daytime light exposure is an important environmental risk factor for mood, sleep, and circadian-related outcomes.
BACKGROUND: 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 environments have blurred this distinction. Negative effects of light exposure at night have been well characterized. The importance of daytime light exposure has been less well characterized. Here we examine the cross-sectional and longitudinal associations of time spent in daytime outdoor light with mood, sleep, and circadian-related outcomes. METHODS: Participants were drawn from the UK Biobank cohort, a large study of UK adults (n = 502,000; 37-73 years old; 54% women). RESULTS: UK Biobank participants reported spending a median of 2.5 daylight hours (IQR = 1.5-3.5 h) outdoors per day. Each additional hour spent outdoors during the day was associated with lower odds of lifetime major depressive disorder (95% CI OR:0.92-0.98), antidepressant usage (OR:0.92-0.98), less frequent anhedonia (OR:0.93-0.96) and low mood (OR:0.87-0.90), greater happiness (OR:1.41-1.48) and lower neuroticism (incident rate ratio, IRR:0.95-0.96), independent of demographic, lifestyle, and employment covariates. In addition, each hour of daytime light was associated with greater ease of getting up (OR:1.46-1.49), less frequent tiredness (OR:0.80-0.82), fewer insomnia symptoms (OR:0.94-0.97), and earlier chronotype (adjusted odds ratio; OR:0.75-0.77). Auto-Regressive Cross-Lagged (ARCL) models were used to examine the longitudinal association of time spent in outdoor light at baseline with later mood-, sleep- and circadian-related outcomes reported at time point 2. Overall, longitudinal associations support cross-sectional findings, though generally with smaller effect sizes. LIMITATIONS: Future studies that examine the intensity of daytime light exposure at the ocular level are needed. CONCLUSIONS: Our findings suggest that low daytime light exposure is an important environmental risk factor for mood, sleep, and circadian-related outcomes.
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