title: Nonlinear reduction in risk for colorectal cancer by oral contraceptive use: a meta-analysis of epidemiological studies.
abstract: OBJECTIVE
  Although the relationship between oral contraceptive (OC) use and colorectal cancer (CRC) risk has been studied extensively, the results of epidemiological studies are controversial. Therefore, we carried out a meta-analysis of epidemiological studies to summarize the available evidence and to quantify the potential dose-response relation.
  
  
  METHODS
  We searched PubMed database for studies of OC use and CRC risk that were published until the end of March 2014. Random- and fixed-effects models were applied to estimate summary relative risks (RRs) and 95 % confidence intervals (CIs).
  
  
  RESULTS
  Twelve cohorts and seventeen case-control studies with a total of 15,790 CRC cases were included in the final analysis. The summary RR for the ever versus never category of OC use was 0.82 (95 % CI 0.76-0.88). Similar result was observed when we compared the longest duration of OC use with the shortest duration (RR = 0.86, 95 % CI 0.76-0.96). Furthermore, the results of stratified analysis were comparable to those of overall meta-analysis. In dose-response analysis, significant inverse associations emerged in nonlinear models for the duration of OC use and CRC (P nonlinearity = 0.001). The greatest risk reduction was observed when the duration of OC use was approximately 42 months. There was moderate heterogeneity in the analysis, and no evidence of small-study bias was observed.
  
  
  CONCLUSIONS
  Based on the findings of this meta-analysis, ever use of OC is associated with lower risk of CRC. Additionally, there is a statistically significant nonlinear inverse association between the duration of OC use and CRC risk.
authors.affiliation: Department of Obstetrics and Gynecology, Shengjing Hospital, China Medical University, Shenyang, People's Republic of China.
authors.forename: Nan-Nan
authors.initials: NN
authors.lastname: Luan
authors.forename: Lang
authors.initials: L
authors.lastname: Wu
authors.forename: Ting-Ting
authors.initials: TT
authors.lastname: Gong
authors.forename: Yong-Lai
authors.initials: YL
authors.lastname: Wang
authors.forename: Bei
authors.initials: B
authors.lastname: Lin
authors.forename: Qi-Jun
authors.initials: QJ
authors.lastname: Wu
mesh_terms: D016022:Case-Control Studies; D015331:Cohort Studies; D015179:Colorectal Neoplasms / Q000453:epidemiology* / Q000209:etiology / Q000517:prevention & control; D003276:Contraceptives, Oral / Q000008:administration & dosage*; D005260:Female; D006801:Humans; D012307:Risk Factors; D013997:Time Factors
chemical_list: D003276:Contraceptives, Oral