title: Acute melatonin administration in humans impairs glucose tolerance in both the morning and evening.
abstract: OBJECTIVE
  To study the effect of melatonin administration on glucose metabolism in humans in the morning and evening.
  
  
  METHODS
  Placebo-controlled, single-blind design.
  
  
  METHODS
  Laboratory assessments.
  
  
  METHODS
  21 healthy women (24 ± 6 y; body mass index: 23.0 ± 3.3 kg/m(2)).
  
  
  METHODS
  Glucose tolerance was assessed by oral glucose tolerance tests (OGTT; 75 g glucose) on 4 occasions: in the morning (9 AM), and evening (9 PM); each occurring 15 minutes after melatonin (5 mg) and placebo administration on 4 non-consecutive days.
  
  
  RESULTS
  Melatonin administration impaired glucose tolerance. When administered in the morning, melatonin significantly increased the incremental area under the curve (AUC) and maximum concentration (Cmax) of plasma glucose following OGTT by 186% and 21%, respectively, as compared to placebo; while in the evening, melatonin significantly increased glucose AUC and Cmax by 54% and 27%, respectively. The effect of melatonin on the insulin response to the OGTT depended on the time of day (P < 0.05). In the morning, melatonin decreased glucose tolerance primarily by decreasing insulin release, while in the evening, by decreasing insulin sensitivity.
  
  
  CONCLUSIONS
  Acute melatonin administration in humans impairs glucose tolerance in both the morning and evening. When administering melatonin, the proximity to meal timing may need to be considered, particularly in those at risk for glucose intolerance.
authors.affiliation: Department of Physiology, University of Murcia, IMIB-Arrixaca, Murcia, Spain.
authors.forename: Patricia
authors.initials: P
authors.lastname: Rubio-Sastre
authors.affiliation: Division of Sleep and Circadian Disorders, Brigham and Women's Hospital, and Division of Sleep Medicine, Harvard Medical School, Boston, MA.
authors.forename: Frank A J L
authors.initials: FA
authors.lastname: Scheer
authors.affiliation: Department of Physiology, University of Murcia, IMIB-Arrixaca, Murcia, Spain.
authors.forename: Purificación
authors.initials: P
authors.lastname: Gómez-Abellán
authors.affiliation: Department of Physiology, University of Murcia, IMIB-Arrixaca, Murcia, Spain.
authors.forename: Juan A
authors.initials: JA
authors.lastname: Madrid
authors.affiliation: Department of Physiology, University of Murcia, IMIB-Arrixaca, Murcia, Spain.
authors.forename: Marta
authors.initials: M
authors.lastname: Garaulet
mesh_terms: D000328:Adult; D019540:Area Under Curve; D001786:Blood Glucose / Q000032:analysis; D015992:Body Mass Index; D005260:Female; D018149:Glucose Intolerance / Q000139:chemically induced; D005951:Glucose Tolerance Test; D006801:Humans; D007328:Insulin / Q000097:blood / Q000378:metabolism; D007333:Insulin Resistance; D000078790:Insulin Secretion; D008550:Melatonin / Q000008:administration & dosage / Q000494:pharmacology*; D016037:Single-Blind Method; D013997:Time Factors; D055815:Young Adult
chemical_list: D001786:Blood Glucose; D007328:Insulin; D008550:Melatonin
keywords: glucose tolerance; insulin resistance; melatonin; metabolic syndrome; oral glucose tolerance test