Cortisol excretion levels and daytime sleep in one-year-old infants

Urine was collected from 20 one-year-old infants from the time of awakening in the moring for 8 consecutive h. Free cortisol was measured by competitive protein-binding analysis in each urine sample. The mean cortisol excretion rate for the entire collection period was .228 +/- .019 mug/h/kg. The mean excretion rate of sleep related cortisol (1.86 +/- .28 mug/h) was significantly different from the mean rate for awake periods (2.61 +/- .28 mug/h). The difference could not be attributed to time of day. The results suggest a direct relationship between cortisol production and daytime sleep-wake states in the one-year-old.