The biological clock modulates the human cortisol response in a multiplicative fashion

Abstract

Human cortisol levels follow a clear circadian rhythm. We investigated the contribution of alternation of sleep and wakefulness and the circadian clock, using forced desynchrony. Cortisol levels were best described by a multiplication of a circadian and a wake-time component. The human cortisol response is modulated by circadian phase. Exposure to stress at an unnatural phase, as in shift work, is predicted to result in abnormal cortisol levels. Health of shift workers may therefore improve when stress is reduced at times when the clock produces high stress sensitivity.

• Circadian
• forced desynchrony
• HPA-axis
• melatonin
• stress

Acknowledgments

We thank the subject volunteers for their participation and Vibeke Bruinenberg for her practical assistance during the weeks of data collection and Leon Steijvers for programming support. Bühlmann laboratories provided the direct saliva melatonin radioimmunoassay tests as part of their collaboration in the EUCLOCK project.