Objectives: Some epidemiologic studies suggest that adolescent physical activity reduces subsequent breast cancer risk. To examine this question further, we analyzed data on physical activity at age 12 that had been collected as part of the Carolina Breast Cancer Study (CBCS).
Methods: The CBCS is a population-based, case-control study of 527 white and 337 African-American cases and 790 controls, frequency-matched on age and race. Respondents were asked whether, and to what extent, they engaged in four specific activities at age 12 (walking to school, biking to school, competitive training, performing vigorous household chores).
Results: Women who reported participation in any of the four activities had a modest reduction in breast cancer risk (odds ratio (OR): 0.8, 95% confidence interval (CI): 0.6-1.0). Using an index measuring approximate number of activity episodes per week, analyses revealed modest inverse relationships for nearly all levels of activity relative to no reported activity; a weighting of the index by metabolic equivalent scores produced similar results.
Conclusions: Our findings support the hypothesis that adolescent physical activity may protect against adult breast cancer, even at moderate levels.