title: The interaction between early-life body size and physical activity on risk of breast cancer.
abstract: While early-life body leanness is associated with increased breast cancer risk, early-life physical activity may protect against breast cancer. We examined whether the excess risk among lean girls is modified by their levels of prior, concurrent, or future physical activity. We conducted an analysis among 74,723 women in the Nurses' Health Study II (follow-up 1997-2011). Participants recalled their body size at ages 5, 10 and 20 years in 1989 using a 9-level pictogram (Level 1 most lean). In 1997, they reported adolescent levels of physical activity (ages 12-13 and 14-17 years). Cox proportional hazards models estimated the overall association of body size with breast cancer risk and assessed interactions of adolescent physical activity with body size at three different age periods (5-10, 10-20 and 20 years), adjusting for early-life and adult risk factors for breast cancer. Regardless of levels of adolescent physical activity, early-life body leanness (level 1-2 vs. 4.5+) was significantly associated with higher breast cancer risk. The association was slightly attenuated among those who were active (60+ MET-hr/wk) during adolescence compared to those who were inactive (<30 MET-hr/wk) (body size at ages 5-10 years: hazard ratio = 1.37, 95% confidence interval = 1.04-1.81 vs. 1.66, 1.29-2.12), but the interaction was not significant (p = 0.72). The results were similar for body size at three different age periods. Being lean during early life is a risk factor for breast cancer among both inactive and active girls. Adolescent physical activity did not significantly modify the association, although some interaction cannot be excluded.
authors.affiliation: Department of Epidemiology, Harvard School of Public Health, Boston, MA.|Channing Division of Network Medicine, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, MA.|Department of Nutrition, Harvard School of Public Health, Boston, MA.
authors.forename: Hannah
authors.initials: H
authors.lastname: Oh
authors.affiliation: Department of Epidemiology, Harvard School of Public Health, Boston, MA.|Channing Division of Network Medicine, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, MA.
authors.forename: Caroline E
authors.initials: CE
authors.lastname: Boeke
authors.affiliation: Department of Epidemiology, Harvard School of Public Health, Boston, MA.|Channing Division of Network Medicine, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, MA.
authors.forename: Rulla M
authors.initials: RM
authors.lastname: Tamimi
authors.affiliation: Department of Epidemiology, Harvard School of Public Health, Boston, MA.|Department of Nutrition, Harvard School of Public Health, Boston, MA.
authors.forename: Stephanie A
authors.initials: SA
authors.lastname: Smith-Warner
authors.affiliation: Department of Epidemiology, Harvard School of Public Health, Boston, MA.|Channing Division of Network Medicine, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, MA.|Department of Biostatistics, Harvard School of Public Health, Boston, MA.
authors.forename: Molin
authors.initials: M
authors.lastname: Wang
authors.affiliation: Department of Epidemiology, Harvard School of Public Health, Boston, MA.|Channing Division of Network Medicine, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, MA.|Department of Nutrition, Harvard School of Public Health, Boston, MA.
authors.forename: Walter C
authors.initials: WC
authors.lastname: Willett
authors.affiliation: Department of Epidemiology, Harvard School of Public Health, Boston, MA.|Channing Division of Network Medicine, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, MA.
authors.forename: A Heather
authors.initials: AH
authors.lastname: Eliassen
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D049628:Body Size; D001943:Breast Neoplasms / Q000453:epidemiology* / Q000209:etiology*; D002648:Child; D002675:Child, Preschool; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008875:Middle Aged; D009043:Motor Activity; D011446:Prospective Studies; D012307:Risk Factors; D057566:Self Report; D011795:Surveys and Questionnaires; D055815:Young Adult
keywords: body fatness; breast cancer; early life; overweight; physical activity