The Development of Circadian Rhythms in Human Infants

separate methods were applied to the same data (Krieger et al., 1971, Santiago et al.,
1996, Price et al., 1983, de Weerth et al., 2003, Antonini et al., 2006).
Using a single definition for circadian rhythmicity (as applied to melatonin and
cortisol samples) within the same group of infants in the same study, in this research,
adds strength to the findings discussed in this section, as there is comparability and
consistency, which will be absent if different methods are compared from different
groups of infants.
Atkinson demonstrated (Atkinson, 1995) large variability in the daily cortisol
excretion with marked differences for individual infants. This may reflect normal
variation due environmental cues. It is possible that outlying infants with significantly
higher values were undergoing a response to inter current infection or stress (Jansen et
al., 2010). An inappropriate cortisol response to stress or illness may reflect
immaturity of physiological and immune systems, which expose the infant to a greater
degree of vulnerability (Wailoo et al., 2003, Westaway et al., 1995). This, together
with the observation that early development of cortisol rhythmicity appears to be
crucial, could prove an important and noteworthy finding for the fuller understanding
of infant physiological development and subsequent susceptibility to disease and
mortality should development be delayed.
This study has highlighted some interesting findings in light of previously published
work of other authors. The role of cortisol and development of its rhythmicity
warrants further study.
215