title: The relationship between physical activity and 2-hydroxyestrone, 16alpha-hydroxyestrone, and the 2/16 ratio in premenopausal women (United States).
abstract: OBJECTIVE
  Estrogen is metabolized in the body through two mutually exclusive pathways yielding metabolites with different biological activities: the low estrogenic 2-hydroxyestrone (2-OHE1) and the highly estrogenic 16alpha-hydroxyestrone (16alpha-OHE1). The ratio of these metabolites (2/16) may be predictive of risk for developing breast cancer. Early evidence has demonstrated that exercise may alter estrogen metabolism to favor the weak estrogen, 2-OHE1.
  
  
  METHODS
  Seventy-seven eumenorrheic females completed physical activity logs for two weeks prior to providing a luteal phase urine sample. Concentrations of 2-OHE1 and 16alpha-OHE1 were measured and the 2/16 ratio computed. Hierarchical regression, controlling for age and body mass index (BMI), was used to determine relationships between estrogen metabolites and daily physical activity.
  
  
  RESULTS
  Regression analyses indicated significant positive relationships between physical activity and 2-OHE1 and the 2/16 ratio (p < 0.05) that appears to be independent of BMI. 16alpha-OHE1 was not significantly related to physical activity.
  
  
  CONCLUSIONS
  These results indicate that physical activity may modulate estrogen metabolism to favor the weak estrogen, 2-OHE1, thus producing a higher 2/16 ratio. This alteration in estrogen metabolism may represent one of the mechanisms by which increased physical activity reduces breast cancer risk.
authors.affiliation: Sport and Exercise Science, BNCC Campus Box 6, University of Northern Colorado, Greeley, CO 80639, USA. ann.bentz@unco.edu
authors.forename: Ann T
authors.initials: AT
authors.lastname: Bentz
authors.forename: Carole M
authors.initials: CM
authors.lastname: Schneider
authors.forename: Kim C
authors.initials: KC
authors.lastname: Westerlind
mesh_terms: D000293:Adolescent; D000328:Adult; D015415:Biomarkers / Q000032:analysis / Q000378:metabolism; D015992:Body Mass Index; D001943:Breast Neoplasms / Q000517:prevention & control*; D015444:Exercise; D005260:Female; D006801:Humans; D006894:Hydroxyestrones / Q000378:metabolism* / Q000652:urine; D008875:Middle Aged; D010809:Physical Fitness / Q000502:physiology*; D011237:Predictive Value of Tests; D017697:Premenopause / Q000378:metabolism* / Q000502:physiology; D011446:Prospective Studies; D012044:Regression Analysis; D018570:Risk Assessment; D012494:Sampling Studies; D018709:Statistics, Nonparametric; D016482:Urinalysis
chemical_list: D015415:Biomarkers; D006894:Hydroxyestrones