Time spent in outdoor light is associated with mood, sleep, and circadian rhythm-related outcomes: a cross-sectional and longitudinal study in over 400,000 UK Biobank participants

Angus C. Burns, Richa Saxena, Céline Vetter, Andrew J.K. Phillips, Jacqueline M. Lane, Sean Cain,
Time spent in outdoor light is associated with mood, sleep, and circadian rhythm-related outcomes: a cross-sectional and longitudinal study in over 400,000 UK Biobank participants, Journal of Affective Disorders, 2021, ISSN 0165-0327 https://doi.org/10.1016/j.jad.2021.08.056.
(https://www.sciencedirect.com/science/article/pii/S0165032721008612)

Highlights

  • Greater time in outdoor light was associated with lowered odds of lifetime major depressive disorder•
  • More daylight predicted better outcomes across a range of mood and sleep measures•
  • These relationships held in both cross-sectional and longitudinal analyses

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 hours) 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). 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 daytime light exposure is a relevant environmental risk factor for mood-, sleep-, and circadian-related outcomes. These findings support the increased daytime light exposure as beneficial for both mood and sleep disorders.

https://www.sciencedirect.com/science/article/abs/pii/S0165032721008612

© 2021 Elsevier B.V. All rights reserved.

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