Light affects morning salivary cortisol in humans.
The effect of light on the morning-cortisol peak in humans was investigated in fourteen healthy men by exposing them to darkness and to light of 800 lux during a 1-h period on two subsequent mornings. In the early morning, we demonstrated a temporary increase of salivary cortisol levels after awakening, while light exposure resulted in a +/- 35% further increase in cortisol levels. Cortisol levels 20 and 40 min after waking were significantly higher during 800 lux exposure than during darkness. In order to investigate the time-dependency, the experiment was repeated in the late evening. In the evening, light had no effect on cortisol levels. These results demonstrate that light conditions in the early morning have a strong impact on the morning-cortisol peak, but that evening cortisol levels are unaffected by light. The possible role of the circadian pacemaker as mediator of the light effect on cortisol level is discussed.
Scheer
F A
FA
Dept. Hypothalamic Integration Mechanisms, Netherlands Institute for Brain Research, Amsterdam.
Buijs
R M
RM
D000328:Adult; D002940:Circadian Rhythm; D006801:Humans; D006854:Hydrocortisone / Q000378:metabolism*; D008027:Light; D008297:Male; D012463:Saliva / Q000378:metabolism*
D006854:Hydrocortisone