title: The role of hormones in the differences in the incidence of breast cancer between Mongolia and the United Kingdom.
abstract: BACKGROUND
  There are striking differences in breast cancer incidence between Asian and western women. Rates vary substantially within Asia also, with Mongolia's even lower than China's. These profound differences have been speculated to be due in part to diet, mediated by circulating hormone concentrations.
  
  
  METHODS
  Sex steroid hormone concentrations were measured in women living in Ulaanbaatar, Mongolia and the United Kingdom (U.K.). Diet was obtained by interview and national survey data. Mean hormone differences were compared by country, and systematic variation by number of days since last menstrual period was modeled and adjusted for age and parity; difference in overall area under the curves was assessed.
  
  
  RESULTS
  The diet in Mongolia was higher in meat and dairy than in the U.K. Mean testosterone concentrations were 18.5% lower (p<0.0001) while estradiol concentrations were 19.1% higher (p = 0.02) in Mongolian than British women, adjusted for age and parity. Progesterone was almost 50% higher in Mongolian women (p = 0.04), particularly during the follicular phase and early luteal surge. Hormone concentrations generally were similar in Mongolian women born in Ulaanbaatar compared with those born in rural areas, although there was a decreasing progesterone trend by degree of westernization (rural Mongolia; urban Mongolia; U.K.). Mean hormone differences were similar when restricted to parous women, and with further adjustment for body mass index, height, and smoking status.
  
  
  CONCLUSIONS
  These data augment accumulating evidence that circulating estrogens are unlikely to explain reduced breast cancer rates in Asia compared with the west, and suggest casting a wider net with respect to biomarkers. Lower testosterone and higher progesterone in Mongolian women raise the possibility that these hormones may be important to consider. In addition, the almost exclusive dietary reliance of Mongolians on meat and dairy argues against beneficial effects of a low-fat diet on circulating hormones explaining international breast cancer differences.
authors.affiliation: Epidemiology and Biostatistics Program, Division of Cancer Epidemiology and Genetics, National Cancer Institute, National Institutes of Health, Department of Health and Human Services, Rockville, Maryland, 20850, United States of America.
authors.forename: Rebecca
authors.initials: R
authors.lastname: Troisi
authors.affiliation: Departments of Nutrition and Epidemiology, Harvard School of Public Health, Boston, Massachusetts, 02115, United States of America; Health Sciences University of Mongolia, Ulaanbaatar, Mongolia.
authors.forename: Daavasambuu
authors.initials: D
authors.lastname: Ganmaa
authors.affiliation: Department of Non-communicable Disease Epidemiology, London School of Hygiene and Tropical Medicine, London, WC1E 7HT, England, United Kingdom.
authors.forename: Isabel
authors.initials: I
authors.lastname: dos Santos Silva
authors.affiliation: Health Sciences University of Mongolia, Ulaanbaatar, Mongolia.
authors.forename: Dambadarjaa
authors.initials: D
authors.lastname: Davaalkham
authors.affiliation: Epidemiology and Biostatistics Program, Division of Cancer Epidemiology and Genetics, National Cancer Institute, National Institutes of Health, Department of Health and Human Services, Rockville, Maryland, 20850, United States of America.
authors.forename: Philip S
authors.initials: PS
authors.lastname: Rosenberg
authors.affiliation: Channing Laboratory, Department of Medicine, and Connors Center for Women's Health and Gender Biology, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts, 02115, United States of America.
authors.forename: Janet
authors.initials: J
authors.lastname: Rich-Edwards
authors.affiliation: Department of Pediatric Oncology, Dana Farber Cancer Institute, Boston, Massachusetts, 02115, United States of America.
authors.forename: Lindsay
authors.initials: L
authors.lastname: Frasier
authors.affiliation: Epidemiology and Biostatistics Program, Division of Cancer Epidemiology and Genetics, National Cancer Institute, National Institutes of Health, Department of Health and Human Services, Rockville, Maryland, 20850, United States of America.
authors.forename: Lauren
authors.initials: L
authors.lastname: Houghton
authors.affiliation: Faculty of Health Sciences, Simon Fraser University, Burnaby, BC V5A 1S6, Canada.
authors.forename: Craig
authors.initials: C
authors.lastname: Janes
authors.affiliation: Departments of Obstetrics and Gynecology, and Preventive Medicine, University of Southern California Los Angeles, Keck School of Medicine, Los Angeles, California, 90033, United States of America.
authors.forename: Frank
authors.initials: F
authors.lastname: Stanczyk
authors.affiliation: Epidemiology and Biostatistics Program, Division of Cancer Epidemiology and Genetics, National Cancer Institute, National Institutes of Health, Department of Health and Human Services, Rockville, Maryland, 20850, United States of America.
authors.forename: Robert N
authors.initials: RN
authors.lastname: Hoover
mesh_terms: D000328:Adult; D001943:Breast Neoplasms / Q000453:epidemiology* / Q000378:metabolism*; D004032:Diet; D005260:Female; D006728:Hormones / Q000378:metabolism*; D006801:Humans; D015994:Incidence; D008875:Middle Aged; D008986:Mongolia / Q000453:epidemiology; D010298:Parity; D011247:Pregnancy; D017697:Premenopause; D006113:United Kingdom / Q000453:epidemiology
chemical_list: D006728:Hormones