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.
Level 3 - non-randomized controlled study
Large observational cohort study with cross-sectional and longitudinal analyses
PubMed 34488088 · doi:10.1016/j.jad.2021.08.056
What was done
Cross-sectional and longitudinal associations were analyzed between self-reported time spent in daytime outdoor light and mood, sleep, and circadian outcomes in UK Biobank participants (aged 37–73 years, 54% women). Models adjusted for demographic, lifestyle, and employment covariates. Auto-Regressive Cross-Lagged (ARCL) models evaluated longitudinal relationships between baseline outdoor light exposure and subsequent outcomes at follow-up.
What was found
Participants reported a median of 2.5 hours of daylight outdoors per day (IQR: 1.5–3.5 h). Each additional daily hour spent outdoors was associated with lower odds of lifetime major depressive disorder (OR: 0.92–0.98), antidepressant use (OR: 0.92–0.98), less frequent anhedonia (OR: 0.93–0.96), less frequent low mood (OR: 0.87–0.90), greater happiness (OR: 1.41–1.48), and lower neuroticism (IRR: 0.95–0.96). It was also linked to greater ease of getting up (OR: 1.46–1.49), less tiredness (OR: 0.80–0.82), fewer insomnia symptoms (OR: 0.94–0.97), and earlier chronotype (adjusted OR: 0.75–0.77). Longitudinal ARCL models supported the cross-sectional directions, though with smaller effect sizes (exact longitudinal numbers not reported in abstract).
Why it matters
While nighttime light exposure is a well-known disruptor, this study provides large-scale evidence that insufficient daytime light exposure is independently associated with worse mood, sleep disturbance, and circadian delay.
Limits
Time spent outdoors and clinical/sleep outcomes were based on self-report rather than objective ocular light dosimetry or actigraphy. The observational design cannot definitively establish causality or eliminate residual confounding from unmeasured outdoor behaviors. The UK Biobank cohort is restricted to adults aged 37–73 and subject to healthy volunteer selection bias.
Cited by
- supports Being in dim or dark environments during the early hours of the day increases the risk of developing mild or severe depression.