Acute effects of bright light exposure on cortisol levels.
Level 2 - randomized trial
Individual within-subject controlled laboratory trial
PubMed 20484692 · doi:10.1177/0748730410368413
What was done
Twenty healthy men and women participated in a within-subject experimental protocol in a time-cue-free environment for 9 to 10 days. Subjects received a 6.7-hour exposure of bright light (approximately 10,000 lux) or dim light (approximately 3 lux) during the biological night and morning, targeting the rising and descending phases of the circadian rhythm of cortisol. Plasma cortisol levels were measured.
What was found
Bright light exposure significantly reduced plasma cortisol levels at both circadian phases studied, whereas dim light exposure had little effect. The abstract reports no numerical values or effect sizes.
Why it matters
It demonstrates that photic input acutely suppresses cortisol secretion in humans during high-secretion circadian phases, helping clarify prior inconsistent literature.
Limits
Sample size was small (n = 20) and restricted to healthy adults in an artificial time-isolated environment. The prolonged duration (6.7 hours) and high intensity (10,000 lux) may not reflect common real-world light exposures. Exact numerical values were not provided in the abstract.
Cited by
- supports A study showed that exposing humans to 10,000 lux bright light for seven hours a day lowered their cortisol response during the rising phase.