Getting rhythm: how do babies do it?

Arch Dis Child Fetal Neonatal Ed. 2015 Jan;100(1):F50-4. doi: 10.1136/archdischild-2014-306104. Epub 2014 Sep 22.


Objectives: To investigate the emergence of biological rhythms in the first months of life in human infants, by measuring age-related changes in core body temperature during night-time sleep, hormones (cortisol and 6-sulfatoxymelatonin) and the expression of a clock-controlled gene H3f3b in oral epithelial cells.

Design: Observational longitudinal study.

Setting: We measured overnight core body temperature, actigraphy, day-night urinary cortisol and 6-sulfatoxymelatonin, as well as circadian gene expression, in infants at home from March 2007 to July 2008 in Leicester.

Participants: We recruited 35 healthy Caucasian infants who were born at term. They were monitored from 6 to 18 weeks of age.

Results: At 8 weeks of age the day-night rhythm of cortisol secretion was the first to appear followed by 6-sulfatoxymelatonin 1 week later; at the same time that night-time sleep was established. At 10 weeks, the maximum fall in deep body temperature occurred with the onset of night-time sleep, followed at 11 weeks by the rhythmical expression of the H3f3b gene.

Conclusions: In human infants, there is a clear sequential pattern for the emergence of diurnal biological rhythms between 6 and 18 weeks of postnatal age, led by the secretion of cortisol and linked with the establishment of consolidated night-time sleep. It is likely that this represents part of a maturation and adaption process as infants gain equilibrium with their external environment after birth.

Keywords: Fetal Medicine; SIDS; Sleep.

Publication types

  • Observational Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Actigraphy
  • Body Temperature / physiology*
  • Body Temperature Regulation / physiology
  • Circadian Rhythm / physiology*
  • Female
  • Gene Expression Regulation / physiology
  • Humans
  • Hydrocortisone / metabolism
  • Hydrocortisone / physiology*
  • Hydrocortisone / urine
  • Infant
  • Male
  • Melatonin / analogs & derivatives*
  • Melatonin / urine
  • Sleep / physiology*


  • 6-sulfatoxymelatonin
  • Melatonin
  • Hydrocortisone