title: The circadian rhythm of tryptophan in breast milk affects the rhythms of 6-sulfatoxymelatonin and sleep in newborn.
abstract: BACKGROUND
  The hormone melatonin regulates the sleep and this pineal hormone is synthesized in the organism from the amino acid tryptophan. It is known that breast-fed babies have better sleep patterns and a better entrained sleep/wake cycle than bottle-fed babies (adapted formula).
  
  
  OBJECTIVE
  To compare the circadian rhythm of 6-sulfatoxymelatonin (aMT6s)--the metabolite of melatonin excreted in the urine--in urine of bottle-fed and breast-fed children, and relate it to the circadian rhythm of tryptophan in breast milk, also evaluating the possible effects on the baby's night-time rest.
  
  
  METHODS
  16 infants of 12 weeks of age were studied, divided into two groups depending on their exclusively natural or artificial feeding. The circadian rhythm of 6-sulfatoxymelatonin in urine was measured for the two groups of infants and for the breast-feeding mothers. In the breast milk, the circadian rhythm of the amino acid tryptophan was measured. The rest of the infants was tested by wrist actimeters for a week and the sleep parameters of the infants were measured and evaluated.
  
  
  RESULTS
  The tryptophan in the breast milk presented a circadian rhythm with acrophase at around 03:00. This affected the 6-sulfatoxymelatonin circadian rhythm with acrophase at 06:00 in the breast-fed infants, and also promoted nocturnal sleep. Assumed sleep, actual sleep, and sleep efficiency were significantly increased in the breast fed infants with respect the formula fed infants.
  
  
  CONCLUSIONS
  A temporal relationship was observed between the circadian rhythm of 6-sulfatoxymelatonin of the exclusively breast-fed babies and that of tryptophan in the mother's milk. Acting this amino acid as a zeitgeber entrainment of the biological rhythms in the breast-fed infant.
authors.affiliation: Department of Physiology, Faculty of Science, Extremadura University, Avda de Elvas s/n, 06071 Badajoz, Spain.
authors.forename: J
authors.initials: J
authors.lastname: Cubero
authors.forename: V
authors.initials: V
authors.lastname: Valero
authors.forename: J
authors.initials: J
authors.lastname: Sánchez
authors.forename: M
authors.initials: M
authors.lastname: Rivero
authors.forename: H
authors.initials: H
authors.lastname: Parvez
authors.forename: A B
authors.initials: AB
authors.lastname: Rodríguez
authors.forename: C
authors.initials: C
authors.lastname: Barriga
mesh_terms: D001903:Bottle Feeding; D001942:Breast Feeding; D002940:Circadian Rhythm / Q000502:physiology*; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D008550:Melatonin / Q000031:analogs & derivatives* / Q000652:urine; D008895:Milk, Human / Q000378:metabolism*; D012016:Reference Values; D012890:Sleep / Q000502:physiology*; D018709:Statistics, Nonparametric; D014364:Tryptophan / Q000378:metabolism*
chemical_list: C054513:6-sulfatoxymelatonin; D014364:Tryptophan; D008550:Melatonin