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.
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.
Ruhayel
Yasir
Y
CRC, Department of Clinical Sciences, Lund University, Malmö University Hospital, Malmö, Sweden. yasir.ruhayel@med.lu.se
Malm
Gunilla
G
Haugen
Trine B
TB
Henrichsen
Trine
T
Bjørsvik
Cathrine
C
Grotmol
Tom
T
Saether
Thomas
T
Malm
Johan
J
Figenschau
Yngve
Y
Rylander
Lars
L
Levine
Richard J
RJ
Giwercman
Aleksander
A
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
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