title: Seasonal variation in serum concentrations of reproductive hormones and urinary excretion of 6-sulfatoxymelatonin in men living north and south of the Arctic Circle: a longitudinal study.
abstract: OBJECTIVE
  Seasonal variation in photoperiod or temperature may influence human reproductive biology. The present study evaluated whether seasonal changes occurred in the levels of reproductive hormones and the major melatonin metabolite, 6-sulfatoxymelatonin (aMT6s), in populations exposed to extreme variation in photoperiod and temperature.
  
  
  METHODS
  Two separate cohorts of Norwegian men were recruited from the general population in either of two locations: Tromsø (69.5 degrees N, n = 92) or Oslo (60 degrees N, n = 112), located north and south of the Arctic Circle (66.5 degrees N), respectively.
  
  
  METHODS
  Four blood and 12-h overnight urine samples were obtained on separate occasions over a 12-month period, including during the photoperiod maximum and minimum. Serum concentrations of FSH, LH, testosterone (T), oestradiol (E(2)), SHBG and the urinary excretion of aMT6s were assessed.
  
  
  RESULTS
  Statistical analysis using generalized estimating equations indicated that LH levels were lowest during early winter in both locations (both P = 0.01). In Tromsø, free T and E(2) concentrations peaked during early winter (P = 0.02 and 0.003, respectively). In Oslo, free T levels were lowest during early winter (P = 0.06) whereas E(2) levels were lowest during late summer (P < 0.001). Urinary aMT6s concentrations were lowest during early summer in Tromsø and Oslo. Concentrations peaked during early winter in Tromsø (P < 0.001) and during late winter in Oslo (P < 0.001).
  
  
  CONCLUSIONS
  LH levels exhibited similar changes in both locations, whereas the patterns of changes of the sex steroid concentrations differed, possibly indicating different underlying mechanisms. Excretion of aMT6s was lowest during early summer in both locations, indicating that the long natural photoperiod was sufficient to cause suppression of melatonin secretion. Whether these changes have any biological significance remains uncertain.
authors.affiliation: CRC, Department of Clinical Sciences, Lund University, Malmö University Hospital, Malmö, Sweden. yasir.ruhayel@med.lu.se
authors.forename: Yasir
authors.initials: Y
authors.lastname: Ruhayel
authors.forename: Gunilla
authors.initials: G
authors.lastname: Malm
authors.forename: Trine B
authors.initials: TB
authors.lastname: Haugen
authors.forename: Trine
authors.initials: T
authors.lastname: Henrichsen
authors.forename: Cathrine
authors.initials: C
authors.lastname: Bjørsvik
authors.forename: Tom
authors.initials: T
authors.lastname: Grotmol
authors.forename: Thomas
authors.initials: T
authors.lastname: Saether
authors.forename: Johan
authors.initials: J
authors.lastname: Malm
authors.forename: Yngve
authors.initials: Y
authors.lastname: Figenschau
authors.forename: Lars
authors.initials: L
authors.lastname: Rylander
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Levine
authors.forename: Aleksander
authors.initials: A
authors.lastname: Giwercman
mesh_terms: D000328:Adult; D001110:Arctic Regions; D015415:Biomarkers / Q000097:blood / Q000652:urine; D004958:Estradiol / Q000097:blood; D005640:Follicle Stimulating Hormone / Q000097:blood; D012739:Gonadal Steroid Hormones / Q000097:blood*; D006801:Humans; D007986:Luteinizing Hormone / Q000097:blood; D008297:Male; D008550:Melatonin / Q000031:analogs & derivatives* / Q000652:urine; D009664:Norway; D017440:Photoperiod; D011446:Prospective Studies; D012621:Seasons; D012738:Sex Hormone-Binding Globulin / Q000032:analysis; D013739:Testosterone / Q000097:blood
chemical_list: D015415:Biomarkers; D012739:Gonadal Steroid Hormones; D012738:Sex Hormone-Binding Globulin; C054513:6-sulfatoxymelatonin; D013739:Testosterone; D004958:Estradiol; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone; D008550:Melatonin