title: Urinary melatonin levels and postmenopausal breast cancer risk in the Nurses' Health Study cohort.
abstract: BACKGROUND
  Melatonin seems to play a role in breast cancer etiology, but data addressing the association between melatonin levels and breast cancer risk in postmenopausal women is sparse.
  
  
  METHODS
  We conducted a nested case-control study in the Nurses' Health Study cohort. First spot morning urine was collected from 18,643 cancer-free women from March 2000 through December 2002. The concentration of the major metabolite of melatonin, 6-sulfatoxymelatonin (aMT6s), was available for 357 postmenopausal women who developed incident breast cancer through May 31, 2006, along with 533 matched control subjects. We used multivariable conditional logistic regression models to investigate associations. All statistical tests were two sided.
  
  
  RESULTS
  An increased concentration of urinary aMT6s was statistically significantly associated with a lower risk of breast cancer (odds ratio for the highest versus lowest quartile of morning urinary aMT6s, 0.62; 95% confidence interval, 0.41-0.95; P(trend) = 0.004). There was no apparent modification of risk by hormone receptor status of breast tumors, age, body mass index, or smoking status.
  
  
  CONCLUSIONS
  Results from this prospective study add substantially to the growing literature that supports an inverse association between melatonin levels and breast cancer risk.
authors.affiliation: Channing Laboratory, 181 Longwood Avenue, Boston, MA 02115, USA. eva.schernhammer@channing.harvard.edu
authors.forename: Eva S
authors.initials: ES
authors.lastname: Schernhammer
authors.forename: Susan E
authors.initials: SE
authors.lastname: Hankinson
mesh_terms: D000328:Adult; D014408:Biomarkers, Tumor / Q000652:urine; D001943:Breast Neoplasms / Q000652:urine*; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D016015:Logistic Models; D008550:Melatonin / Q000652:urine*; D008875:Middle Aged; D017698:Postmenopause / Q000652:urine*; D011446:Prospective Studies; D012306:Risk; D012307:Risk Factors; D011795:Surveys and Questionnaires; D014481:United States
chemical_list: D014408:Biomarkers, Tumor; D008550:Melatonin