The Development of Circadian Rhythms in Human Infants

Melatonin secretion was higher on nights infants were well and lower on nights they
exhibited signs of illness (ratio of increase = 2.3 weeks; 95% CI 0.98 to 5.41 weeks;
p= 0.055). It was also lower in infants from poorer families (see section 9.1.4). Night
time melatonin secretion had a tendency to be higher in infants put to bed earlier and
who had shorter sleep latencies. This was not significant.
No factors were shown to have an effect on cortisol secretion. This contrasts with
previous work, which demonstrated a significant difference in cortisol secretion in
economically deprived infants when compared to infants from affluent families
(Wailoo et al., 2003). It may be that in this group of infants, measurements of cortisol
should have been commenced early enough in the first postnatal weeks to demonstrate
an appreciable change from low cortisol levels to high levels. To investigate what
factors affect cortisol production, it may be necessary to examine these during the
period levels are changing (earlier in the infants‟ developmental process and postnatal
life; or possibly even in the foetal stage) rather than when they have already possibly
plateaued and stabilised.
Sleep efficiency was directly related to infants‟ temperature related physiological
state. Infants with mature temperature rhythm were more sleep efficient (ß coefficient
- 9; 95% CI -16 to -1.8; p= 0.015). Sleeping in the same room as the carer also
improved sleep efficiency (-1.57; 95% CI -2.62 to 0.53; p=0.004).
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