An epidemiologic investigation of physical activity and breast cancer risk in Africa.

BACKGROUND: Physical activity (PA) is modifiable and linked to decreased breast cancer risk but its impact has not been investigated among indigenous African populations.
METHODS: From 2011 to 2013, 558 cases and 1,014 controls were recruited into the African Breast Cancer Study in Nigeria, Cameroon, and Uganda, and completed a culturally tailored PA questionnaire that assesses habitual PA the year before diagnosis/interview. PA sub-scores (housework, occupational, and leisure PA) and a total PA score were calculated (metabolic equivalent of task, MET-hours/day). Multiple logistic regressions were performed, adjusting for age, body mass index (BMI), study sites, and menopausal status. The models were then stratified by BMI and study site, respectively.
RESULTS: The overall PA score among controls (17.8 MET-hours/day on average) was mainly composed by housework PA and occupational PA with little leisure PA (7.0, 10.3, and 0.5 MET-hours/day, respectively). Multivariable analyses showed that PA was significantly associated with reduced breast cancer risk in both pre- and postmenopausal women (up to 60% risk reduction), with a dose-responsive relationship (Ptrend < 0.001). The inverse association was strong among lean women, less strong but still significant among overweight women, but not existing among obese women. The inverse association held for all intensity-level and domains of PA.
CONCLUSIONS: PA of African women mainly consists of housework and work-related activities. The preliminary data show that PA may be significantly associated with reduced breast cancer risk. IMPACT: An inverse association between PA and breast cancer risk was observed among indigenous African women, a unique and understudied population. ©2014 American Association for Cancer Research.