Related Experiment Video
Updated: Jul 19, 2026

In Vitro Bioluminescence Assay to Characterize Circadian Rhythm in Mammary Epithelial Cells
Published on: September 28, 2017
Human circadian rhythms: physiological and therapeutic relevance of light and melatonin
Debra J Skene1, Josephine Arendt
1Centre for Chronobiology, School of Biomedical and Molecular Sciences, University of Surrey, Guildford GU2 7XH, UK. d.skene@surrey.ac.uk
Abstract:
Ocular light plays a key role in human physiology by transmitting time of day information. The production of the pineal gland hormone melatonin is under the control of the light-dark cycle. Its profile of secretion defines biological night and it has been called the 'darkness hormone'. Light mediates a number of non-visual responses, such as phase shifting the internal circadian clock, increasing alertness, heart rate and pupil constriction. Both exogenous melatonin and light, if appropriately timed, can phase shift the human circadian system. These 'chronobiotic' effects of light and melatonin have been used successfully to alleviate and correct circadian rhythm disorders, such as those experienced following travel across time zones, in night shift work and in circadian sleep disorders. The effectiveness of melatonin and light are currently being optimized in terms of time of administration, light intensity, duration and wavelength, and melatonin dose and formulation. The aim of this review is not to replicate information that has been reported in a number of reviews of the human circadian timing system and the role of melatonin and light, but rather to extract findings relevant to the field of clinical biochemistry.
Related Concept Videos
Circadian Rhythms and Gene Regulation
Circadian Rhythms and Gene Regulation
Management of Insomnia
Chronopharmacokinetics: Circadian Rhythms and Influence on Drug Response
The time of drug administration is an important factor to consider, as it can influence the toxic dose of a drug. For example, a study conducted by Prins et al. in 1997 examined the effects of the timing of...
Biological Clocks and Seasonal Responses
Understanding Sleep
The circadian rhythm, a nearly 24-hour cycle, is deeply influenced by environmental light cues. Light exposure directly affects the hypothalamus, which in turn regulates...