Childhood and teenage physical activity and breast cancer risk
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Adult physical activity is associated with reduced breast cancer risk, but few studies have evaluated activity before adulthood. Early life may be an important period because of rapid breast development and hormonal changes. This study contributes new information by examining childhood (ages 5–12) and teenage (ages 13–19) activity separately and overall.
The Sister Study is a cohort of 50,884 women aged 35–74. Women reported age 5–19 sports/exercise activities and age 10 and 16 unstructured activities. Both hours and MET-hours of activity were considered in association with breast cancer overall, by ER status, and by menopausal status. Hazard ratios (HRs) and 95% confidence intervals (CIs) were calculated with Cox proportional hazards models.
2416 cases were diagnosed during follow-up (mean = 6.4 years). Participation in 7+ hours (vs <1 h) per week of sports/exercise during ages 5–19 was associated with reduced breast cancer risk (HR = 0.75; 95% CI 0.57–0.99). 7+ hours (vs <1 h) per week of unstructured physical activity at age 16, but not age 10, was inversely associated with breast cancer (HR = 0.81; 95% CI 0.70–0.95). Associations were more pronounced for ER+ tumors, especially for activity during the childhood (ages 5–12) period. Due to low correlation between childhood/teenage and adulthood activity in this study (r = 0.1), it is unlikely that recent activity explains our results.
Findings from this large cohort indicate higher levels of physical activity during ages 5–19 are inversely associated with breast cancer risk, supporting early life as a window of susceptibility for breast cancer development.
KeywordsChildhood Early life Physical activity Breast cancer
The authors appreciate the helpful review by Drs. Hazel Nichols and Lawrence Engel.
This work was supported by the National Institute of Environmental Health Sciences training grant to the University of North Carolina (T32ES007018) and by the Intramural Research Program of the NIH, National Institute of Environmental Health Sciences (Z01-ES044005).
Compliance with ethical standards
Conflict of interest
The authors declare they have no conflict of interest.
All procedures performed in studies involving human participants were in accordance with the ethical standards of Institutional Review Boards of the National Institute of Environmental Health Sciences, National Institutes of Health, and the Copernicus Group and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. This article does not contain any studies with animals performed by any of the authors.
Informed consent was obtained from all individual participants included in the Sister Study.
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