title: Stability, precision, and near-24-hour period of the human circadian pacemaker.
abstract: 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.
authors.affiliation: Circadian, Neuroendocrine, and Sleep Disorders Section, Division of Endocrinology, Department of Medicine, Harvard Medical School, Brigham and Women's Hospital, 221 Longwood Avenue, Boston, MA 02115, USA.
authors.forename: C A
authors.initials: CA
authors.lastname: Czeisler
authors.forename: J F
authors.initials: JF
authors.lastname: Duffy
authors.forename: T L
authors.initials: TL
authors.lastname: Shanahan
authors.forename: E N
authors.initials: EN
authors.lastname: Brown
authors.forename: J F
authors.initials: JF
authors.lastname: Mitchell
authors.forename: D W
authors.initials: DW
authors.lastname: Rimmer
authors.forename: J M
authors.initials: JM
authors.lastname: Ronda
authors.forename: E J
authors.initials: EJ
authors.lastname: Silva
authors.forename: J S
authors.initials: JS
authors.lastname: Allan
authors.forename: J S
authors.initials: JS
authors.lastname: Emens
authors.forename: D J
authors.initials: DJ
authors.lastname: Dijk
authors.forename: R E
authors.initials: RE
authors.lastname: Kronauer
mesh_terms: D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology*; D001683:Biological Clocks / Q000235:genetics / Q000502:physiology*; D001831:Body Temperature; D002940:Circadian Rhythm / Q000235:genetics / Q000502:physiology*; D003624:Darkness; D005260:Female; D006801:Humans; D006854:Hydrocortisone / Q000097:blood; D008027:Light; D008297:Male; D008550:Melatonin / Q000097:blood; D008875:Middle Aged; D012890:Sleep
chemical_list: D008550:Melatonin; D006854:Hydrocortisone