title: A cross-sectional analysis of light at night, neighborhood sociodemographics and urinary 6-sulfatoxymelatonin concentrations: implications for the conduct of health studies.
abstract: BACKGROUND
  There is accumulating evidence that circadian disruption, mediated by alterations in melatonin levels, may play an etiologic role in a wide variety of diseases. The degree to which light-at-night (LAN) and other factors can alter melatonin levels is not well-documented. Our primary objective was to evaluate the degree to which estimates of outdoor environmental LAN predict 6-sulftoxymelatonin (aMT6s), the primary urinary metabolite of melatonin. We also evaluated other potential behavioral, sociodemographic, and anthropomorphic predictors of aMT6s.
  
  
  METHODS
  Study participants consisted of 303 members of the California Teachers Study who provided a 24-hour urine specimen and completed a self-administered questionnaire in 2000. Urinary aMT6s was measured using the Bühlmann ELISA. Outdoor LAN levels were estimated from satellite imagery data obtained from the U.S. Defense Meteorological Satellite Program's (DMSP) Operational Linescan System and assigned to study participants' geocoded residential address. Information on other potential predictors of aMT6s was derived from self-administered surveys. Neighborhood socioeconomic status (SES) was based on U.S. Census block group data.
  
  
  RESULTS
  Lower aMT6s levels were significantly associated with older age, shorter nights, and residential locations in lower SES neighborhoods. Outdoor sources of LAN estimated using low-dynamic range DMSP data had insufficient variability across urban neighborhoods to evaluate. While high-dynamic range DMSP offered much better variability, it was not significantly associated with urinary aMT6s.
  
  
  CONCLUSIONS
  Future health studies should utilize the high-dynamic range DMSP data and should consider other potential sources of circadian disruption associated with living in lower SES neighborhoods.
authors.forename: Susan
authors.initials: S
authors.lastname: Hurley
authors.forename: David O
authors.initials: DO
authors.lastname: Nelson
authors.forename: Erika
authors.initials: E
authors.lastname: Garcia
authors.forename: Robert
authors.initials: R
authors.lastname: Gunier
authors.forename: Andrew
authors.initials: A
authors.lastname: Hertz
authors.forename: Peggy
authors.initials: P
authors.lastname: Reynolds
mesh_terms: D000328:Adult; D000368:Aged; D015415:Biomarkers / Q000652:urine; D002140:California / Q000453:epidemiology; D002940:Circadian Rhythm / Q000502:physiology*; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008029:Lighting / Q000009:adverse effects* / Q000191:economics*; D008297:Male; D008550:Melatonin / Q000031:analogs & derivatives* / Q000652:urine; D008875:Middle Aged; D012111:Residence Characteristics; D012959:Socioeconomic Factors
chemical_list: D015415:Biomarkers; C054513:6-sulfatoxymelatonin; D008550:Melatonin