In order to better understand the “environmental contributors to geographic variation in breast density in urban and rural areas,” this study evaluated the effect of breast density and air pollution.

BACKGROUND: There has been evidence to suggest that women in urban areas tend to have higher breast density than those living rurally. It has also been established that there are definite air pollution patterns between urban and rural areas, and “some air pollutants are known to have endocrine-disrupting properties.” These factors indicate the possible association between some air pollutants and breast density.

METHOD: Women (≥40 years old) who had screening mammograms within the Breast Cancer Surveillance Consortium and had a known postcode were included. The air pollutants investigated were fine particles <2.5 μm in diameter (PM2.5) and ozone (O3). A variety of compounds can make up PM2.5, including those with endocrine-disrupting and carcinogenic properties, which explains it’s importance in this study.

RESULTS: It was found that a “one-unit increase in PM2.5 concentration was associated with 4% increased chance of having heterogeneously dense breasts.” Whereas a “one-unit increase in O3 concentration was associated with 3% lower chance of having extremely dense breasts.”

CONCLUSION: This study was able to show “positive associations between breast density and PM2.5 and inverse associations between breast density and O3…These chemical constituents could potentially influence breast density by interfering with normal proliferation, thus increasing the relative amount of fibroglandular tissue in the breast, and subsequently, breast density.”