title: Indicators for the total duration of premenopausal endogenous estrogen exposure in relation to BMD.
abstract: BACKGROUND
  Previous studies have shown that age at menopause is an important indicator of duration of endogenous estrogen exposure. The present study investigates whether combining more information on reproductive factors is useful in estimating individual total duration of exposure to endogenous estrogens.
  
  
  METHODS
  Bone mineral density (BMD) was used as operational outcome. The study population consisted of 3476 white women living in Eindhoven, The Netherlands, aged 46-57 years, either pre- (n = 2420) or postmenopausal (n = 1056). BMD of the lumbar spine was measured by dual X-ray absorptiometry. Information on reproductive factors was obtained with questionnaires.
  
  
  RESULTS
  The number of reproductive years explained 4.8% of the variance in BMD, while age at menopause alone accounted for 3.6%. Duration of lactation or oral contraceptive use did not add to the proportion of variance explained. The effect of reproductive years on BMD was stronger in older women. No significant associations with BMD were found for other reproductive variables. The number of miscarriages in premenopausal women (beta = 0.00760, SE = 0.00357, P = 0.03) explained only 0.16% of the variance in BMD.
  
  
  CONCLUSIONS
  We conclude that it is not necessary to use more reproductive factors besides age at menopause and menarche in determining total duration of endogenous estrogen exposure.
authors.affiliation: Julius Center for Health Sciences and Primary Care, University Medical Center Utrecht, Room D 01.335, PO Box 85500, 3508 GA Utrecht, The Netherlands.
authors.forename: Maria L C
authors.initials: ML
authors.lastname: Hagemans
authors.forename: Yvonne T
authors.initials: YT
authors.lastname: van der Schouw
authors.forename: Miriam J J
authors.initials: MJ
authors.lastname: de Kleijn
authors.forename: Wija A
authors.initials: WA
authors.lastname: van Staveren
authors.forename: Victor J M
authors.initials: VJ
authors.lastname: Pop
authors.forename: Geraline L
authors.initials: GL
authors.lastname: Leusink
authors.forename: Diederick E
authors.initials: DE
authors.lastname: Grobbee
mesh_terms: D000022:Abortion, Spontaneous / Q000453:epidemiology; D000375:Aging / Q000378:metabolism / Q000502:physiology; D015992:Body Mass Index; D015519:Bone Density; D004967:Estrogens / Q000378:metabolism*; D005260:Female; D006801:Humans; D015994:Incidence; D008572:Menarche; D008875:Middle Aged; D017698:Postmenopause / Q000378:metabolism; D017697:Premenopause / Q000378:metabolism*; D013997:Time Factors
chemical_list: D004967:Estrogens