American Journal of Epidemiology Vol. 152, No. 12 : 1129-1135
Copyright © 2000 by The Johns Hopkins University School of Hygiene and Public Health
ORIGINAL CONTRIBUTIONS |
Lactation Reduces Breast Cancer Risk in Shandong Province, China
1 Department of Epidemiology and Public Health, Yale University School of Medicine and Yale Cancer Center, New Haven, CT.
2 Department of Toxicology and Epidemiology, Institute of Occupational Medicine, Shandong Academy of Medical Science, Jinan, China.
3 Department of Epidemiology and Biostatistics, McGill University, Montreal, Canada.
4 Department of Epidemiology and Disease Surveillance, Chinese Academy of Preventive Medicine, Beijing, China.
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 
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.
breast feeding; breast neoplasms; case-control studies; lactation; reproductive history
Abbreviations: CI, confidence interval
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