The Development of Circadian Rhythms in Human Infants

There then fails to be consensus on the exact timing of the appearance of an adult
circadian pattern as reported by de Weerth et al (de Weerth et al., 2003).
Differences in the timing of maturity of hypothalamic- pituitary- adrenal axis, as
found by the individual research groups, may be due to the fact that each group used
different definitions as to what constituted a circadian rhythm. Also the frequency
samples were taken and methodologies in the studies were not comparable (see
discussion section 11.3). In some cases sample sizes were relatively small. There
have been a range of ages, quoted in the literature, at which infants have been thought
to obtain a mature circadian rhythm of cortisol production: from as early as 8 weeks
of age (Santiago et al., 1996); to as late as 9 months of age (de Weerth & van Geert,
2002). Clearly the occurrence of the event has not been pinpointed to an exact time
and the variability is wide. Use of a uniform and consistent definition of timing of
circadian rhythmicity will allow meaningful comparisons and measuring different
aspect of physiological maturation in the same babies at the same time has an obvious
advantage.
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