The role of sunlight in sleep regulation: analysis of morning, evening and late exposure

Oct 7, 2025BMC public health

How sunlight exposure at different times of day relates to sleep regulation

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Abstract

Every 30-minute increment of morning sun exposure is associated with a 23-minute reduction in the .

The midpoint of sleep is significantly affected by sunlight exposure, especially in the morning.
Sunlight exposure after 3 p.m. is associated with a lesser reduction in the midpoint of sleep (-19 minutes).
Increased morning sun exposure correlates with a lower score, indicating improved sleep quality.
No significant associations were found between sunlight exposure and total sleep time, sleep latency, or sleep efficiency.

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BACKGROUND: Recent lifestyle changes have reduced sunlight exposure, impacting circadian rhythms and sleep regulation. This study investigates how sunlight exposure at different times of the day affects sleep parameters.

METHODS: This cross-sectional study included 1,762 adults from the Iron Quadrilateral region, Brazil, and was conducted between October and December 2020. Sunlight exposure was self-reported for three periods: before 10 a.m., between 10 a.m. and 3 p.m., and after 3 p.m. Sleep quality was assessed using the (PSQI), which also provided information on total sleep time (total minutes slept), sleep latency (time to fall asleep), sleep efficiency (ratio of time spent asleep to time in bed), and the (the halfway point between sleep onset and wake-up time, indicative of circadian rhythm alignment). Associations between sunlight exposure and sleep outcomes were evaluated using linear regression models, adjusted for sociodemographic and behavioral variables.

RESULTS: The midpoint of sleep was the most affected sleep parameter, showing significant associations with sunlight exposure across all timeframes, particularly in the morning. Every 30-minute increment of morning sun exposure (before 10 a.m.) was associated with a 23-minute reduction in the midpoint of sleep (-0:23 hh: mm; 95%CI: -0:36, -0:10; beta: -0.387; 95%CI: -0.607, -0.166). Sunlight exposure after 3 p.m. also reduced the midpoint of sleep but to a lesser extent (-0:19 hh: mm; 95%CI: -0:36, -0:03; beta: -0.325; 95%CI: -0.600, -0.051). Furthermore, an increase in morning sun exposure was significantly associated with a lower PSQI total score, improving sleep quality (beta: -0.184; 95%CI: -0.362, -0.006). No significant associations were observed between sunlight exposure and total sleep time, latency, or efficiency.

CONCLUSION: Morning sunlight exposure influences the regulation of the sleep midpoint and overall sleep quality. These findings highlight the potential role of morning sun exposure in aligning circadian rhythms and improving sleep health.

Key numbers

23 minutes

Reduction in

For every 30-minute increase in morning sunlight exposure

19 minutes

Reduction in

For every 30-minute increase in sunlight exposure after 3 p.m.

0.184 points

score reduction

For every 30-minute increase in morning sunlight exposure

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The role of sunlight in sleep regulation: analysis of morning, evening and late exposure

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