Breast cancer incidence in Nigeria has risen by > 120% since 2000. Its mortality rate (18.8 / 100 000 women / year) ranks highest in Africa. Studies have suggested that non-vigorous physical activity is associated with reduced risk of breast cancer. However, its role in breast cancer risk is yet to be established in sub-Saharan Africa. Increasing prevalence of behaviours associated with reduced non-vigorous physical activity has been reported across several countries in sub-Saharan Africa, including Nigeria. The purpose of this study was to investigate if there is an association between non-vigorous physical activity and breast cancer risk among Nigerian women.
The study was a multisite hospital based case-control design involving 379 histologically confirmed breast cancer cases and 403 controls. The participants were interviewed in-person between October 2016 and May 2017. Cases were selected from the oncology wards and controls from ophthalmology wards. Self-reported non vigorous physical activity (sum of occupational, household and transport physical activities) was summarised as both hours per week and metabolic equivalents hours per week (MET-hr / wk). Data were analyzed using multivariable logistic regression, adjusting for known confounders.
The result (in MET-hr/wk) showed a 40% [95 % confidence interval (CI): 0.40 - 0.89, p for trend = 0.032] reduction in breast cancer risk among women in the upper tertile of total non-vigorous physical activity compared to those in the lowest tertile of non-vigorous physical activity. This was stronger among younger [ odds ratio (OR) 0. 54, 95 % CI: 0.32 - 0.92], premenopausal (OR 0.46, 95% CI: 0.24 - 0.89) and lean women (OR 0.47; 95% CI: 0.25 - 0.88) compared to older, postmenopausal and overweight/obese women respectively.
Non-vigorous physical activity was associated with reduced risk of breast cancer among Nigerian women. This risk reduction was modified by age, menopausal status and body mass index. Conditions that promote increased participation in non-vigorous physical activity among women should therefore be encouraged with respect to breast cancer prevention in Nigeria.
Samuel Onyinyechukwu Azubuike.
National Open University of Nigeria.
All authors have declared no conflicts of interest.