title: Early menarche is associated with increased risk of asthma: Prospective population-based study of twins.
abstract: OBJECTIVE
  To examine the association between early menarche and risk of post-menarcheal asthma.
  
  
  METHODS
  Using data from two multidisciplinary questionnaire surveys, conducted eight years apart, we prospectively studied 10,648 female twins, 12-41 years of age, from the nationwide Danish Twin Registry. Early menarche was defined as menarche before 12 years of age. We performed a cohort analysis and a co-twin control analysis including twin pairs discordant for incident asthma.
  
  
  RESULTS
  Early menarche was observed in 9.3% of the individuals. The eight-year cumulative incidence of asthma was higher in girls with early menarche compared to girls without early menarche (7.4 vs. 4.5%), OR = 1.71 (1.31-2.22), p < 0.001; also after adjustment for BMI, current age, physical activity, education, and smoking, OR = 1.53 (1.15-2.04), p = 0.003. The unadjusted risk of asthma was increased by 8% (1-15%), p = 0.041 per year earlier menarche occurred. Among 167 twin pairs discordant for incident asthma, there was a non-significant tendency towards early menarche being more common in the asthmatic than the non-asthmatic co-twin (12.0 vs. 9.6%), OR = 1.57 (0.61-4.05), p = 0.350. The risk of asthma was not uniform in discordant monozygotic and dizygotic twins.
  
  
  CONCLUSIONS
  Early menarche is associated with increased risk of asthma among Danish female twins independently of BMI, age, physical activity, educational level and smoking. Results indicate a complex relationship possibly mediated through innate and non-genetic effects.
authors: Department of Respiratory Medicine, Bispebjerg Hospital, Bispebjerg Bakke 23, DK-2400 Copenhagen NV, Denmark.
authors: Sofie
authors: S
authors: Lieberoth
authors: Department of Respiratory Medicine, Bispebjerg Hospital, Bispebjerg Bakke 23, DK-2400 Copenhagen NV, Denmark.
authors: Elisabeth
authors: E
authors: Gade
authors: Institute of Regional Health Services Research, Odense Patient Data Explorative Network & The Danish Twin Registry, University of Southern Denmark, DK-5000 Odense C, Denmark.
authors: Kirsten Ohm
authors: KO
authors: Kyvik
authors: Department of Respiratory Medicine, Bispebjerg Hospital, Bispebjerg Bakke 23, DK-2400 Copenhagen NV, Denmark.
authors: Vibeke
authors: V
authors: Backer
authors: Department of Respiratory Medicine, Bispebjerg Hospital, Bispebjerg Bakke 23, DK-2400 Copenhagen NV, Denmark. Electronic address: simonfrancisthomsen@gmail.com.
authors: Simon Francis
authors: SF
authors: Thomsen
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D001249:Asthma / Q000453:epidemiology* / Q000235:genetics; D002648:Child; D003718:Denmark / Q000453:epidemiology; D004200:Diseases in Twins / Q000453:epidemiology*; D005260:Female; D006801:Humans; D016015:Logistic Models; D008572:Menarche / Q000235:genetics / Q000502:physiology*; D011446:Prospective Studies; D012042:Registries; D012307:Risk Factors; D012907:Smoking / Q000453:epidemiology; D014427:Twins / Q000706:statistics & numerical data*; D055815:Young Adult
keywords: Asthma; Epidemiology; Genetics; Menarche; Twin study