Journal
PSYCHONEUROENDOCRINOLOGY
Volume 108, Issue -, Pages 28-34Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.psyneuen.2019.05.016
Keywords
Non-visual light-effects; Cortisol; Melanopsin-expressing-Retinal-Ganglion-Cells; Cortisol-awakening-response
Categories
Funding
- Federal Ministry of Education and Research (BMBF), Germany
- subproject: Einfluss von Licht auf die hormonelle Stressverarbeitung [influence of light on hormonal stress management] as part of the joint project: Nicht-visuelle Lichtwirkungen [non -visual effects of light] [13N13397]
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Background: It is assumed that the expression of the cortisol awakening response (CAR) is modulated by light exposure during the peri-awakening period. While initial evidence supports this principal effect, the specific role of the spectral composition of light (brightness and wavelength) is still incompletely understood. Method: Two counterbalanced within-subject experiments were conducted in a standardized sleep laboratory setting to investigate the effect of light intensity (study I; two days: dim vs. bright light) and spectral composition (study II; three days: red vs. blue vs. green light) on the CAR. Across studies, light exposure was conducted for one-hour post-awakening and the accuracy of CAR assessments (based on eight saliva samples) was well-controlled in line with recent guidelines. Results: The two studies revealed consistent effects of light exposure on the CAR. Specifically, an increased CAR was found after exposure to bright (vs. dim) light (study I; (F-(3.7,F- 106.4) = 11.93, p < .001, eta(2)(p) = .29) and following blue and green (vs. red) light exposure (study II; F-(4.9,F- 194.6) = 2.49, p = .037, eta(2)(p) = .10). Conclusion: Our findings illustrate the crucial role of light intensity and wavelength for expression of the CAR, in line with current theoretical knowledge of underlying neurobiological mechanisms.
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