title: Breastfeeding and thyroid cancer risk in women: A dose-response meta-analysis of epidemiological studies.
abstract: The association between breastfeeding and thyroid cancer risk is not consistent from epidemiological studies. To better clarify the association including assessing a potential dose-response relationship, we conducted a comprehensive meta-analysis.
  
  
  
  We searched PubMed (MEDLINE) up to November 2015 for prospective studies or case-control studies that evaluated the association between breastfeeding and risk of thyroid cancer. Effect estimates were pooled using a fixed-effects model.
  
  
  
  Nine reports (2 prospective studies, 6 case-control studies and 1 pooled analysis of 14 case-control studies) involving 2423 cases and 350,081 non-cases were identified. After pooling relevant studies, there was a significant inverse association between ever breastfeeding and risk of thyroid cancer (RR = 0.91, 95% CI 0.83-0.99), with minor heterogeneity (I(2) = 10.1%). The dose-response analysis revealed a significant linear relationship between the duration of breastfeeding and risk of thyroid cancer. The summary RR for an increment of 1 month of breastfeeding with risk of thyroid cancer was 0.983 (95% CI 0.98-0.99). When focusing on cohort studies, a more prominent linear dose-response relationship was detected, with the combined RR for every increment of 1 month of breastfeeding to be 0.965 (95% CI 0.96-0.97).
  
  
  
  This meta-analysis suggests that breastfeeding is potentially inversely associated with thyroid cancer risk. Also longer duration of breastfeeding may further decreases thyroid cancer risk. If validated in large-scale prospective studies, our findings may have implications for impacting women's decision in breastfeeding.
authors.affiliation: Department of Neurology, The People's Hospital of Deyang City, Deyang 618000, Sichuan, China.
authors.forename: Xingyang
authors.initials: X
authors.lastname: Yi
authors.affiliation: Program of Quantitative Methods in Education, University of Minnesota, Minneapolis, MN, 55455, USA; Division of Epidemiology, Department of Medicine, Vanderbilt Epidemiology Center, Vanderbilt-Ingram Cancer Center, Vanderbilt University School of Medicine, Nashville, TN 37203, USA.
authors.forename: Jingjing
authors.initials: J
authors.lastname: Zhu
authors.affiliation: Guangdong Provincial Key Laboratory of Medical Molecular Diagnostics, Dongguan Scientific Research Center, Guangdong Medical University, Dongguan 523808, China.
authors.forename: Xiao
authors.initials: X
authors.lastname: Zhu
authors.affiliation: Department of Neurology, Taihe Hospital Affiliated to Hubei University of Medicine, Shiyan City, Hubei Province 442000, China. Electronic address: liuguangjian@aliyun.com.
authors.forename: Guang Jian
authors.initials: GJ
authors.lastname: Liu
authors.affiliation: Division of Epidemiology, Department of Medicine, Vanderbilt Epidemiology Center, Vanderbilt-Ingram Cancer Center, Vanderbilt University School of Medicine, Nashville, TN 37203, USA; Center for Clinical and Translational Science, Mayo Clinic, Rochester, MN, 55905, USA. Electronic address: lang.wu@vanderbilt.edu.
authors.forename: Lang
authors.initials: L
authors.lastname: Wu
mesh_terms: D001942:Breast Feeding; D016021:Epidemiologic Studies; D005260:Female; D006801:Humans; D012307:Risk Factors; D013964:Thyroid Neoplasms / Q000453:epidemiology* / Q000517:prevention & control*
keywords: Breastfeeding; Epidemiological studies; Meta-analysis; Risk; Thyroid cancer