title: Lactation reduces breast cancer risk in Shandong Province, China.
abstract: Results from studies of western populations investigating lactation and breast cancer risk have been inconsistent. To examine this issue, the authors conducted a hospital-based case-control study in Shandong Province, China, in 1997-1999. A total of 404 cases and an equal number of controls were included. Detailed information regarding lactation, menstruation, and reproduction was collected through in-person interview. The authors found a significant inverse association between duration of lactation and breast cancer risk. For women who breastfed for more than 24 months per child, the odds ratio was 0.46 (95% confidence interval (CI): 0.27, 0.78) when compared with those who breastfed for 1-6 months per child. A significantly reduced risk of breast cancer was also found for those whose lifetime duration of lactation totaled 73-108 months (odds ratio = 0.47, 95% CI: 0.23, 0.95) and for those who breastfed for > or =109 months (odds ratio = 0.24, 95% CI: 0.11, 0.53). The test for trend was statistically significant for both mean duration of lactation per child (p = 0.02) and lifetime duration of lactation (p = 0.00). Further stratification by menopausal status resulted in the same conclusion. These data suggest that prolonged lactation reduces breast cancer risk.
authors.affiliation: Department of Epidemiology and Public Health, Yale University School of Medicine and Yale Cancer Center, New Haven, CT, USA. tongzhang.zheng@yale.edu
authors.forename: T
authors.initials: T
authors.lastname: Zheng
authors.forename: L
authors.initials: L
authors.lastname: Duan
authors.forename: Y
authors.initials: Y
authors.lastname: Liu
authors.forename: B
authors.initials: B
authors.lastname: Zhang
authors.forename: Y
authors.initials: Y
authors.lastname: Wang
authors.forename: Y
authors.initials: Y
authors.lastname: Chen
authors.forename: Y
authors.initials: Y
authors.lastname: Zhang
authors.forename: P H
authors.initials: PH
authors.lastname: Owens
mesh_terms: D000293:Adolescent; D000328:Adult; D017677:Age Distribution; D001942:Breast Feeding; D001943:Breast Neoplasms / Q000175:diagnosis / Q000453:epidemiology*; D016022:Case-Control Studies; D002681:China / Q000453:epidemiology; D016001:Confidence Intervals; D005260:Female; D006801:Humans; D015994:Incidence; D016015:Logistic Models; D008875:Middle Aged; D016017:Odds Ratio; D018570:Risk Assessment; D012424:Rural Population; D012494:Sampling Studies; D013997:Time Factors