Takeaway
- A cross-sectional and longitudinal association was seen between daytime light exposure and mood, sleep, and circadian-related outcomes.
Why this matters
- Findings warrant further research to better understand the role of light in the pathophysiology of mood and sleep disorders by directly measuring circadian physiology and daytime light exposure in a well-controlled longitudinal design.
Study design
- A large scale cohort study of 502,000 participants (age, 37-73 years) from the UK Biobank who spent a median of 2.5 hours (interquartile range, 1.5-3.5 hours) daily in outdoor light during the daytime.
- Funding: None.
Key results
- In cross-sectional analysis, greater time spent in outdoor light during the day was associated with:
- lower risk of lifetime recurrent major depressive disorder (adjusted OR [aOR], 0.96; 95% CI, 0.92-0.98) and antidepressant use (aOR, 0.95; 95% CI, 0.92-0.98);
- greater self-reported happiness (aOR, 1.45; 95% CI, 1.41-1.48);
- lower neuroticism (incidence rate ratio, 0.96; 95% CI, 0.95-0.96); and
- less frequent low mood (aOR, 0.88; 95% CI, 0.87-0.89) and anhedonia (aOR, 0.95; 95% CI, 0.93-0.96).
- Furthermore, greater time spent in outdoor light during the day was associated with (aOR; 95% CI):
- earlier chronotype (0.76; 0.75-0.77);
- greater ease of getting up (1.47; 1.46-1.49);
- fewer insomnia symptoms (0.96; 0.94-0.97); and
- less frequent tiredness (0.81; 0.80-0.82).
- Overall, longitudinal associations between time spent in outdoor light and mood, sleep and circadian-related outcomes later were consistent with the cross-sectional findings, but with smaller effect sizes.
Limitations
- Observational design.
This clinical summary originally appeared on Univadis, part of the Medscape Professional Network.
