title: Age at menarche and risk of colorectal cancer: a meta-analysis.
abstract: BACKGROUND
  Various observational studies have focused on the relationship between menarcheal age and the risk of colorectal cancer (CRC). However, the association is still controversial because of inconsistent results. Therefore, we performed a meta-analysis to assess this issue from epidemiological studies.
  
  
  METHODS
  After a literature search in MEDLINE, EMBASE, and Web of Science for studies of menarcheal age and CRC risk published through the end of January 2013, we pooled the relative risks (RRs) from included studies using a fixed- or random-effects model and performed heterogeneity and publication bias analyses. All statistical tests were two-sided.
  
  
  RESULTS
  Eleven case-control and 11 cohort studies were eligible for inclusion in our analysis. The random-effects pooled RR for oldest versus youngest menarcheal age was 0.95 [95% confidence intervals (CIs) = 0.85-1.06], with significant heterogeneity (Q = 61.03, P<0.001, I (2) = 65.6%). When separately analyzed, case-control (RR = 0.95, 95% CI = 0.75-1.21) and cohort studies (RR = 0.97, 95% CI = 0.90-1.04) yielded similar results. Moreover, similar results were also observed among the subgroup analyses by study quality, population, exposure assessment, anatomic cancer site, subsite of colon cancer, and several potential important confounders and risk factors. There was no evidence of publication bias and significant heterogeneity between subgroups detected by meta-regression analyses.
  
  
  CONCLUSIONS
  Findings from this meta-analysis demonstrated that menarcheal age was not associated with the risk of CRC in humans. Further studies are warranted to stratify results by the subsite of colon cancer and menopause status in the future.
authors.affiliation: Department of Gastroenterology, the First Affiliated Hospital of Dalian Medical University, Dalian, China. Lichunyan_dl@163.com
authors.forename: Chun-Yan
authors.initials: CY
authors.lastname: Li
authors.forename: Bo
authors.initials: B
authors.lastname: Song
authors.forename: Ying-Yan
authors.initials: YY
authors.lastname: Wang
authors.forename: Hua
authors.initials: H
authors.lastname: Meng
authors.forename: Shi-Bin
authors.initials: SB
authors.lastname: Guo
authors.forename: Li-Na
authors.initials: LN
authors.lastname: Liu
authors.forename: Hai-Chen
authors.initials: HC
authors.lastname: Lv
authors.forename: Qi-Jun
authors.initials: QJ
authors.lastname: Wu
mesh_terms: D000367:Age Factors; D016022:Case-Control Studies; D015331:Cohort Studies; D015179:Colorectal Neoplasms / Q000175:diagnosis* / Q000473:pathology; D016206:Databases, Bibliographic; D005260:Female; D006801:Humans; D008572:Menarche / Q000502:physiology*; D018570:Risk Assessment; D012307:Risk Factors