Stability, precision, and near-24-hour period of the human circadian pacemaker

Charles A. Czeisler, Jeanne F. Duffy, Theresa L. Shanahan, Emery N. Brown, Jude F. Mitchell, David W. Rimmer, Joseph M. Ronda, Edward J. Silva, James S. Allan, Jonathan S. Emens, Derk Jan Dijk, Richard E. Kronauer

Research output: Contribution to journalArticlepeer-review

1285 Scopus citations


Regulation of circadian period in humans was thought to differ from that of other species, with the period of the activity rhythm reported to range from 13 to 65 hours (median 25.2 hours) and the period of the body temperature rhythm reported to average 25 hours in adulthood, and to shorten with age. However, those observations were based on studies of humans exposed to light levels sufficient to confound circadian period estimation. Precise estimation of the periods of the endogenous circadian rhythms of melatonin, core body temperature, and cortisol in healthy young and older individuals living in carefully controlled lighting conditions has now revealed that the intrinsic period of the human Circadian pacemaker averages 24.18 hours in both age groups, with a tight distribution consistent with other species. These findings have important implications for understanding the pathophysiology of disrupted sleep in older people.

Original languageEnglish (US)
Pages (from-to)2177-2181
Number of pages5
Issue number5423
StatePublished - Jun 25 1999
Externally publishedYes

ASJC Scopus subject areas

  • General


Dive into the research topics of 'Stability, precision, and near-24-hour period of the human circadian pacemaker'. Together they form a unique fingerprint.

Cite this