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QUESTION: Is breastfeeding associated with a decreased risk of breast cancer?
Data sources
{Studies were identified from review articles, computer aided literature searches, and discussions between the authors and their colleagues. The principal investigators of all the studies identified were invited to collaborate. Subsequently, a list of studies and references was sent to collaborators who were then asked if they knew of further studies that were not listed; the principal investigators of those studies were also invited to collaborate.}*
Study selection
Studies were selected if they were cohort or case control studies, had data on ≥100 women with incident invasive breast cancer, and had data on each woman with respect to reproductive factors, including childbearing and breastfeeding.
Data extraction
Data were extracted on total number of pregnancies; age at each pregnancy; outcome of each pregnancy; total number of children breastfed; total (lifetime) duration of breastfeeding; whether each individual live born child had been breastfed, and, …
Footnotes
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For correspondence: Professor V Beral, Radcliffe Infirmary, Oxford, UK. Fax +44 (0)186 531 0545.
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Sources of funding: Cancer Research UK and UNDP/UNFPA/ WHO/World Bank.
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