title: The effect of hormone therapy on serum melatonin concentrations in premenopausal and postmenopausal women: a randomized, double-blind, placebo-controlled study.
abstract: OBJECTIVE
  Melatonin levels decrease physiologically with age, and possibly with the transition to menopause. The plausible influence of hormone therapy (HT) on melatonin is poorly understood. The aim of this randomized, placebo-controlled, double-blind trial was to investigate the effect of HT administration on serum melatonin concentrations in late premenopausal and postmenopausal women.
  
  
  METHODS
  Analyses were carried out among 17 late premenopausal and 18 postmenopausal healthy women who participated in a prospective HT study in Finland. Serum melatonin was sampled at 20-min (21:00-24:00 h; 06:00-09:00 h) and 1-h (24:00-06:00 h) intervals at baseline and after 6 months with HT or placebo.
  
  
  METHODS
  Melatonin levels and secretion profile after 6 months of HT compared to placebo.
  
  
  RESULTS
  Mean melatonin levels, mean melatonin exposure level (area under curve, AUC) and mean duration of melatonin secretion did not differ after 6 months with HT vs. placebo, irrespectively of the reproductive state. However, in postmenopausal women the melatonin peak time (acrophase) was delayed by 2.4h (2 h 21 min) on average after 6 months with HT vs. placebo (p<0.05). No interaction between time and group was detected when melatonin level was modelled before or after treatment.
  
  
  CONCLUSIONS
  Administration of HT to postmenopausal women alters melatonin peak time, but not melatonin levels. Further research on larger clinical samples is needed to better understand the effects of HT on melatonin profile.
authors.affiliation: Department of Mental Health and Substance Abuse Services, National Institute for Health and Welfare (THL), Mannerheimintie 170, Helsinki, Finland. Electronic address: elena.toffol@thl.fi.
authors.forename: Elena
authors.initials: E
authors.lastname: Toffol
authors.affiliation: Sleep Research Unit, Department of Physiology, University of Turku, Lemminkäisenkatu 14-18A, 5th Floor, Turku, Finland; Heart Center, Turku University Hospital and University of Turku, PL 52, Turku, Finland.
authors.forename: Nea
authors.initials: N
authors.lastname: Kalleinen
authors.affiliation: Department of Mental Health and Substance Abuse Services, National Institute for Health and Welfare (THL), Mannerheimintie 170, Helsinki, Finland; Department of Public Health, Hjelt Institute, University of Helsinki, Mannerheimintie 172, Helsinki, Finland.
authors.forename: Jari
authors.initials: J
authors.lastname: Haukka
authors.affiliation: Department of Physiology, University of Oulu, Aapistie 7, Oulu, Finland.
authors.forename: Olli
authors.initials: O
authors.lastname: Vakkuri
authors.affiliation: Department of Mental Health and Substance Abuse Services, National Institute for Health and Welfare (THL), Mannerheimintie 170, Helsinki, Finland.
authors.forename: Timo
authors.initials: T
authors.lastname: Partonen
authors.affiliation: Sleep Research Unit, Department of Physiology, University of Turku, Lemminkäisenkatu 14-18A, 5th Floor, Turku, Finland; Department of Obstetrics and Gynaecology, Turku University Central Hospital and University of Turku, PL 52, Turku, Finland.
authors.forename: Päivi
authors.initials: P
authors.lastname: Polo-Kantola
mesh_terms: D000328:Adult; D000368:Aged; D019540:Area Under Curve; D004311:Double-Blind Method; D004958:Estradiol / Q000008:administration & dosage / Q000031:analogs & derivatives; D015914:Estrogen Replacement Therapy / Q000379:methods*; D005260:Female; D005387:Finland; D006801:Humans; D008550:Melatonin / Q000097:blood*; D008875:Middle Aged; D009640:Norethindrone / Q000008:administration & dosage; D017698:Postmenopause / Q000097:blood*; D017697:Premenopause / Q000097:blood*; D011446:Prospective Studies
chemical_list: D004958:Estradiol; D008550:Melatonin; D009640:Norethindrone
keywords: Acrophase; Hormone replacement; Late premenopause; Postmenopause; Reproduction