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Background:

Many epidemiologic studies have found an association between physical activity and breast cancer risk, although this has not been a consistent finding.

Methods:

Studies were identified through a systematic review of literature available on PubMed through February 2006. We included all cohort and case–control studies that assessed total or leisure time activities in relation to occurrence or mortality of breast cancer. The fully adjusted risk estimates and 95% confidence intervals for the highest versus lowest level of activity were documented for each study as well as evidence for a dose–response relationship. Methodologic quality was also assessed. Due to statistical and methodologic heterogeneity among studies, we did not carry out statistical pooling. To draw conclusions, we performed a best-evidence synthesis taking study quality into account.

Results:

Nineteen cohort studies and 29 case–control …