Sedentary behaviour and risk of breast cancer according to occupation and family size

Abstract

Abstract Background Nowadays there is a lack of consensus on the relationship between sedentary lifestyles and breast cancer (BC). In this study we aim to shed light by analysing the relationship between a sedentary lifestyle and breast cancer in women participating in the Breast Cancer Screening Programme of the Valencian Community (BCSP-VC) (Spain) according to occupation and Family Size (FS). Methods Cohort study with women aged between 45-70 years participating in the BCSP-VC. The sample consists of 506 cases and 120853 controls. Multivariate logistic regression models (M) were performed to study the relationship between sedentary lifestyle and BC. The explanatory variables were: M1: sedentary behaviour adjusted for age and family history; M2: M1 + reproductive variables (menopausal status, hormone replacement therapy, months breastfeeding); M3: M2 + lifestyles (Body Mass Index, smoking); M4: M3 + gender variables (child burden, FS) and M5: M4 + social variables (educational level, occupation). These M are implemented in the total sample and stratified by occupation (manual, non-manual, housewives and non-working) and FS (small, medium, large). Results are given in terms of Odds Ratio (OR) and 95% confidence interval (CI). Results M1 shows that sedentary women are more likely to have BC (OR = 1.25 CI=1.01-1.55). This association is maintained in M2 (OR = 1.25 CI=1.00-1.57) and M3 (OR = 1.25 CI=1.00-1.57) but not when adjusting for gender and social variables. When stratifying by occupation and FS, we observe that, regardless of the variables taken into account in the M, housewives and women with small FS who are sedentary are more likely to have BC (p < 0.05). No statistically significant results were observed in the rest of the occupational and FS strata. Conclusions Sedentary behaviour increases the risk of developing BC, with this relationship being observed in housewives and those with small FS. Further work is needed on how gender and social variables modulate this effect. Key messages Sedentary behaviour increase the risk of breast cancer, and this relationship is affected by gender and social characteristics. The positive relationship between breast cancer and sedentary behaviour is observed in housewives and those with small family size.