title: Hysterectomy, oophorectomy and risk of dementia: a nationwide historical cohort study.
abstract: BACKGROUND
  This study aimed to determine whether there is an association between hysterectomy and dementia.
  
  
  METHODS
  All female Danish residents born before 1966, alive on their 40th birthday and without a dementia diagnosis prior to 1977 (n = 2,313,388) were followed from January 1, 1977, or the age of 40, whichever came later, until dementia diagnosis, death, emigration or December 31, 2006, whichever came first. The relative risks (RR) for developing dementia in women with hysterectomy/oophorectomy compared to referent women were calculated.
  
  
  RESULTS
  Overall, hysterectomy did not increase the risk of dementia. When stratified by age at dementia diagnosis, hysterectomy was associated with an increased risk for early-onset dementia before the age of 50: hysterectomy alone (RR = 1.38, 95% confidence interval (CI) = 1.07-1.78), with unilateral oophorectomy (RR = 2.10, 95% CI = 1.28-3.45), with bilateral oophorectomy (RR = 2.33, 95% CI = 1.44-3.77). The younger the age at hysterectomy/oophorectomy, the greater was the risk.
  
  
  CONCLUSIONS
  Although statistically significant, the association between premenopausal hysterectomy and early-onset dementia is uncertain due to study limitations. Premenopausal bilateral oophorectomy is associated with a higher risk, suggesting a dose effect of premature estrogen deficiency on dementia. The age-dependent effect suggests that the younger brain is probably more vulnerable to estrogen deficiency.
authors.affiliation: Department of Neurology, Neuroscience Center, Copenhagen University Hospital Rigshospitalet, Copenhagen, Denmark. thien.phung@mail.mcgill.ca
authors.forename: Thien Kieu Thi
authors.initials: TK
authors.lastname: Phung
authors.forename: Berit Lindum
authors.initials: BL
authors.lastname: Waltoft
authors.forename: Thomas Munk
authors.initials: TM
authors.lastname: Laursen
authors.forename: Annette
authors.initials: A
authors.lastname: Settnes
authors.forename: Lars Vedel
authors.initials: LV
authors.lastname: Kessing
authors.forename: Preben Bo
authors.initials: PB
authors.lastname: Mortensen
authors.forename: Gunhild
authors.initials: G
authors.lastname: Waldemar
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D015331:Cohort Studies; D003704:Dementia / Q000453:epidemiology*; D003718:Denmark / Q000453:epidemiology; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007044:Hysterectomy / Q000706:statistics & numerical data*; D008498:Medical Record Linkage; D008875:Middle Aged; D010052:Ovariectomy / Q000706:statistics & numerical data*; D017697:Premenopause; D012042:Registries; D012306:Risk; D012307:Risk Factors