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Abstract
Objective: To assess the age at which the circadian rhythm of melatonin begins.
Methods: 55 children, divided into groups from the neonatal period to 24 months of
life, were studied. Urine samples were taken from 28 newborn babies to measure 6-sulfatoxymelatonin
(aMT6s). Salivary samples were collected from infants (27 cases), to measure melatonin
(aMT). aMT was measured by RIA and aMT6s by ELISA using commercial kits. Changes in
the levels of aMT6s and aMT were evaluated using the Friedman test and Wilcoxon matched
pair test. Results: The group aged 27–41 days showed statistically significant differences
in daily aMT6s and aMT concentrations. The highest values were always found between
24.00 and 8.00 h. This day/night difference persisted from 2–3 to 13–24 months of
age. Conclusion: The data indicate that the circadian melatonin rhythm appears at
the end of the neonatal period and persists thereafter.