title: Spring snow lowers human melatonin.
abstract: OBJECTIVE
  We set out to find out in which way seasonal changes of environmental luminosity could affect melatonin secretion in humans.
  
  
  METHODS
  For an entire year we collected every two months nocturnal urine samples from 20 male outdoor workers who lived and worked in an area of the circumpolar region from which exact data solar irradiance and temperature were available.
  
  
  METHODS
  Melatonin secretion rates were assessed with our melatonin-specific radioimmunoassay.
  
  
  RESULTS
  Melatonin secretion was twice as high in December as in April, 0.88 +/- 16 nmol/12 h (mean +/- SE) vs. 0.43 +/- 9 nmol/12 h, p < 0.05. Regression analyses showed that melatonin values best correlated inversely with weeks before the urine samplings were collected was associated with a ca. 50% reduction in melatonin secretion. The association with global irradiance was weaker and none existed with temperature or other environmental variables.
  
  
  CONCLUSIONS
  Light reaching the eyes via the snow or other reflecting involved in certain biological phenomena that exhibit seasonal variations such as reproductive and self-destructive behaviours.
authors.affiliation: Department of Physiology, University of Oulu, Finland. juhani.leppaluoto@oulu.fi
authors.forename: Juhani
authors.initials: J
authors.lastname: Leppäluoto
authors.forename: Kirsti
authors.initials: K
authors.lastname: Sikkilä
authors.forename: Victor Benno
authors.initials: VB
authors.lastname: Meyer-Rochow
authors.forename: Juhani
authors.initials: J
authors.lastname: Hassi
mesh_terms: D001110:Arctic Regions / Q000453:epidemiology; D006801:Humans; D008027:Light; D008297:Male; D008550:Melatonin / Q000378:metabolism* / Q000652:urine; D010507:Periodicity; D011863:Radioimmunoassay; D012044:Regression Analysis; D012621:Seasons
chemical_list: D008550:Melatonin