METHODS: Using data from a cross-sectional study of 9,417 women living in urban or rural areas recruited through hospital- or community-based opportunistic mammography screening programs, we conducted regression and mediation analyses to identify factors contributing to the differences in MD between urban and rural populations across Asian ethnic subgroups.

RESULTS: Consistent with higher risk of breast cancer, age-and-BMI-adjusted percent and absolute MD measurements were significantly higher in women living in urban areas compared to those in rural areas. Mediation analyses showed that differences observed were partly explained by higher parity (7-9%) and breastfeeding (2-3%) among women living in rural areas. Notably, the effect of parity (number of children) was similar in Chinese and Malay women (16-17% and 7-8%, respectively), but not observed in Indian women. Hormonal use, smoking, and physical activity did not predict MD nor mediate the observed association.