title: Urinary levels of melatonin and risk of postmenopausal breast cancer: women's health initiative observational cohort.
abstract: BACKGROUND
  Results from prospective studies on the association between urinary levels of melatonin and risk of postmenopausal breast cancer have been mixed. Several although not all studies have found lower urinary levels of melatonin in women who developed breast cancer compared with cancer-free women.
  
  
  METHODS
  We examined the association between urinary levels of melatonin and breast cancer risk in postmenopausal women in a case-control study nested in the Women's Health Initiative Observational Cohort. Levels of 6-sulfatoxymelatonin were measured in first morning voids from 258 women who later developed breast cancer and from 515 matched controls. Multivariable conditional logistic regression was used to calculate ORs and 95% confidence intervals (CI).
  
  
  RESULTS
  Fully adjusted risk estimates of breast cancer, relative to the lowest quartile level of creatinine-adjusted melatonin, were 1.07 (95% CI, 0.67-1.71), 1.26 (95% CI, 0.79-2.01), and 1.25 (95% CI, 0.78-2.02) for women in the second, third, and highest quartile (Ptrend = 0.27). Comparable results for cases diagnosed less than four years after urinary collection and matched controls were 1.0, 1.25 (95% CI, 0.51-3.06), 1.85 (95% CI, 0.75-4.57), and 1.94 (95% CI, 0.75-5.03; Ptrend = 0.11). Melatonin levels and breast cancer were not associated in cases diagnosed four or more years after urinary collection and matched controls (Ptrend = 0.89).
  
  
  CONCLUSIONS
  We found no evidence that higher urinary levels of melatonin are inversely associated with breast cancer risk in postmenopausal women.
  
  
  CONCLUSIONS
  Accumulating discrepancies in results across studies warrant further exploration.
authors: Authors' Affiliations: Division of Biostatistics and Epidemiology, University of Massachusetts Amherst, Amherst; Division of Preventive and Behavioral Medicine, University of Massachusetts Medical School, Worcester; Division of Preventive Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts; Department of Obstetrics and Gynecology, University of Southern California Keck School of Medicine, Los Angeles, California; Department of Epidemiology and Medicine, Brown University and Rhode Island Hospital, Division of Endocrinology, Department of Medicine, Providence, Rhode Island; and Division of Public Health Sciences, Fred Hutchinson Cancer Research Center, Seattle, Washington.
authors: Susan R
authors: SR
authors: Sturgeon
authors: Ashley
authors: A
authors: Doherty
authors: Katherine W
authors: KW
authors: Reeves
authors: Carol
authors: C
authors: Bigelow
authors: Frank Z
authors: FZ
authors: Stanczyk
authors: Judith K
authors: JK
authors: Ockene
authors: Simin
authors: S
authors: Liu
authors: JoAnn E
authors: JE
authors: Manson
authors: Marian L
authors: ML
authors: Neuhouser
mesh_terms: D000368:Aged; D001943:Breast Neoplasms / Q000652:urine*; D016022:Case-Control Studies; D015331:Cohort Studies; D005260:Female; D006801:Humans; D008550:Melatonin / Q000031:analogs & derivatives* / Q000652:urine; D008875:Middle Aged; D064887:Observational Studies as Topic; D011446:Prospective Studies; D012307:Risk Factors; D016387:Women's Health
chemical_list: C054513:6-sulfatoxymelatonin; D008550:Melatonin