Longitudinal evaluation of the development of salivary cortisol circadian rhythm in infancy
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L B Santiago1, S M Jorge, A C Moreira
1Division of Neonatology, Department of Pediatrics, Faculty of Medicine, University of Sao Paulo, Ribeirao Preto, Brazil.
Insights
Infant cortisol daily rhythm, a marker of adrenal function, emerges earlier than expected. This study used noninvasive saliva samples to track cortisol patterns in healthy newborns, revealing early circadian maturation.
Area of Science:
- Endocrinology
- Pediatrics
- Chronobiology
Background:
- Adrenocortical function exhibits a circadian rhythm in children and adults.
- Limited data exists on the onset of this rhythm in infancy due to sampling challenges.
Purpose of the Study:
- To investigate the age of appearance of the cortisol daily rhythm in healthy infants.
- To utilize noninvasive salivary cortisol measurements for monitoring circadian rhythm development.
Main Methods:
- A longitudinal study involving 9 healthy infants.
- Collection of salivary samples at morning, afternoon, and night across 2 to 24 postnatal weeks.
- Radioimmunoassay (RIA) determination of cortisol levels in salivary samples.
Main Results:
- Cortisol rhythm was established by 2, 4, or 8 weeks in 55% of infants.
- The remaining infants showed rhythm emergence at 12 or 20 weeks.
- The overall mean age for cortisol rhythm emergence was 8 weeks.
Conclusions:
- The development of the hypothalamic-pituitary-adrenal axis circadian maturation in infants may occur earlier than previously thought.
- Noninvasive salivary cortisol monitoring is a viable method for studying infant circadian rhythms.
Objective:
Although an outstanding characteristic of the adrenocortical function of children and adults is its circadian rhythm, little information is available about the age of appearance of such rhythm in infancy. The main obstacle has been the ethical difficulty in obtaining serial blood samples from healthy infants. We monitored the development of cortisol daily rhythm using noninvasive salivary cortisol determination.
Design And Patients:
A longitudinal study of a group of 9 healthy infants was performed. Salivary samples were obtained in the morning, afternoon and night at 2, 4, 8, 12, 16, 20 and 24 post-natal weeks from all infants.
Measurements:
Cortisol was determined by RIA in 25-microl salivary samples. Two techniques based on assay coefficients of variation were employed to characterize a normal circadian pattern of cortisol.
Results:
Five infants (55%) established and maintained their cortisol rhythm as early as at 2, 4 and 8 weeks of age. In the remaining 4 infants the age of appearance was 12 and 20 weeks. This rhythm emerged in the group as a whole at a mean age of 8 weeks.
Conclusions:
Our data suggest that, in most normal infants, the development of hypothalamic-pituitary-adrenal axis circadian maturation may occur at a much earlier age than previously described.