A case–control study of lifetime light intensity physical activity and breast cancer risk
Menée au Canada auprès de 1 110 cas et de 1 172 témoins, cette étude analyse l'association entre une activité physique de faible intensité tout au long de la vie et le risque de cancer du sein
Purpose : Physical activity reduces breast cancer risk, although most evidence is for activity in the moderate-to-vigorous intensity range. The effect of light intensity physical activity (LIPA) is unknown. We aimed to determine the association between self-reported lifetime LIPA and pre- and post-menopausal breast cancer risk. Our secondary objective was to analyze risk stratified by estrogen and progesterone tumor receptor status. Methods : Data were from a case–control study of 1,110 incident breast cancer cases (388 pre-menopausal; 722 post-menopausal) and 1,172 controls (442 pre-menopausal; 730 post-menopausal) recruited at two Canadian sites. Lifetime leisure-time, household, and occupational physical activity and covariates were assessed by questionnaire. Mean minutes per day of LIPA for each of the age periods 12–17, 18–34, 35–49, ≥50, and the total lifetime were calculated. Odds ratios were calculated using unconditional logistic regression for overall breast cancer risk and using polytomous logistic regression for estrogen receptor (ER)/progesterone receptor (PR)-defined tumor subtypes and were adjusted for moderate-to-vigorous physical activity and other confounders. Results : LIPA was not associated with breast cancer risk at any age period across the life course: odds ratio (OR) = 0.81; 95 % CI 0.53–1.24 for pre-menopausal women and OR = 0.87; 95 % CI 0.64–1.19 for post-menopausal women in the highest vs. lowest categories of total lifetime LIPA. No heterogeneity in risk by ER/PR tumor status was observed. Conclusions : Our results suggest that light intensity physical activity is not associated with breast cancer risk reduction. This finding is important for physical activity recommendations for breast cancer prevention.