MELATONIN RHYTHM IN HUMAN-MILK

The pineal hormone melatonin exhibits a circadian rhythm in body fluid s. No data are available on melatonin in human milk. The present study was undertaken to determine whether melatonin is detectable in human milk and, if so, whether it exhibits a daily rhythm. Blood and milk we re sampled between 1400-1700 h and again between 0200-0400 h from 10 m others 3-4 days after delivery. Melatonin in both fluids was beyond th e limit of detection during the day, whereas during the night, its con centration was 280 +/- 34 pmol/L in serum and 99 +/- 26 pmol/L in milk . Six mothers collected milk after each feeding throughout 1 24-h peri od within 3 months after delivery. Melatonin in the milk of all subjec ts exhibited a pronounced daily rhythm, with high levels during the ni ght and undetectable levels during the day. The presence of the rhythm in milk suggests that melatonin fluctuations in milk might communicat e time of day information to breast-fed infants.