title: Sleep timing may modulate the effect of sleep loss on testosterone.
abstract: BACKGROUND
  Sleep loss has been shown to reduce secretory activity of the pituitary-gonadal axis in men, but the determinants of this effect are unknown.
  
  
  OBJECTIVE
  To discriminate the effects of sleep duration and sleep timing on serum concentrations of luteinizing hormone (LH), testosterone (T) and prolactin (PRL).
  
  
  METHODS
  Fifteen young, healthy men (27·1 ± 1·3 years; BMI, 22·9 ± 0·3 kg/m(2) ) were examined in a condition of sleep time restriction to 4 h (bedtime, 02:45 -07:00 h) for two consecutive nights and in a control condition of 8 h regular sleep (bedtime, 22:45-07:00 h). After the second night, serum concentrations of LH, T and PRL were monitored over a 15-h period. In addition, these hormones were measured in serum samples obtained in a further experiment in eight healthy men (24·5 ± 1·1 years; BMI, 23·7 ± 0·6 kg/m(2) ) in the morning after one night of total sleep deprivation, of 4·5 h sleep (bedtime, 22:30-03:30 h), and of regular 7 h sleep (bedtime, 22:30-06:00 h).
  
  
  RESULTS
  Serum LH, T and PRL concentrations showed characteristic diurnal variations across the 15-h period without any differences between the 4- and 8-h sleep conditions. However, total sleep deprivation and 4·5 h of sleep restricted to the first night-half markedly decreased morning T and PRL concentrations (both P ≤ 0·05).
  
  
  CONCLUSIONS
  Collectively, our data suggest that the effect of sleep restriction on pituitary-gonadal secretory activity may be modulated by sleep timing. While sleep loss in the early part of the night does not affect T and PRL, early awakening and wakefulness during the second part of the night reduces morning circulating T and PRL concentrations.
authors.affiliation: Department of Internal Medicine I, University of Luebeck, Luebeck, Germany. sebastian.schmid@uk-sh.de
authors.forename: Sebastian M
authors.initials: SM
authors.lastname: Schmid
authors.forename: Manfred
authors.initials: M
authors.lastname: Hallschmid
authors.forename: Kamila
authors.initials: K
authors.lastname: Jauch-Chara
authors.forename: Hendrik
authors.initials: H
authors.lastname: Lehnert
authors.forename: Bernd
authors.initials: B
authors.lastname: Schultes
mesh_terms: D000328:Adult; D006801:Humans; D007986:Luteinizing Hormone / Q000097:blood; D008297:Male; D011388:Prolactin / Q000097:blood; D012890:Sleep / Q000502:physiology*; D012892:Sleep Deprivation / Q000097:blood*; D007319:Sleep Initiation and Maintenance Disorders / Q000097:blood; D013739:Testosterone / Q000097:blood*; D014851:Wakefulness / Q000502:physiology
chemical_list: D013739:Testosterone; D011388:Prolactin; D007986:Luteinizing Hormone