The effects of light exposure on the cortisol stress response in human males

It is assumed that the production of cortisol is modulated by light exposure. While initial evidence supports this principal effect, the specific effect of light (intensity and wavelength) onto the cortisol stress response is still not completely understood. One between-subject experiment was conducted in a standardized sleep laboratory setting to investigate the effect of light intensity (dim white vs. bright white light) and spectral composition (red vs. blue) on the cortisol response after the Maastricht Acute Stress Test (MAST). 112 healthy young males (24.83 ± 4.10 years of age) were randomly assigned to one of the four light conditions. Across conditions, light exposure was conducted for one-hour post-awakening and the light effect was measured based on eight saliva samples. The analysis indicates significant main effects for time and light condition as well as a significant interaction effect. Notably, bright light exposure evoked the highest cortisol levels when compared to dim white, red, and blue light. Our findings illustrate the crucial role of light intensity and wavelength for the cortisol stress response, in line with current theoretical knowledge of underlying neurobiological mechanisms. LAY SUMMARY Effects of different light sources were tested on healthy male adults in the morning after a stress test. Their stress responses showed that a bright light exposure increased the stress hormone level greatest compared to dim white, red or blue light sources. Findings point toward the crucial role of light intensity associated with the hormonal stress response.