Age of appearance of circadian rhythm in salivary cortisol values in infancy.

Abstract

Samples of saliva (4 in 24 hours), collected at monthly intervals for the first 6 months of life in 8 term infants by their mothers, were analysed for cortisol by radioimmunoassay. Values in the first month were more variable, daily mean values were greater, and amplitudes of variation were greater than in subsequent months. The circadian rhythm appeared by the third month.