Background: Dairy foods are complex mixtures which include nutrients and non-nutrient substances that could potentially influence cancer etiology, including breast cancer. Objective: The purpose of this study was to examine associations between the types and quantity of dairy foods consumed and the risk of breast cancer among women participating in the Roswell Park Cancer Institute Data Bank and BioRepository (DBBR) between 2003 and 2014. Methods: Archived clinical and questionnaire data were obtained from the DBBR from 1941 women diagnosed with breast cancer between December 2003 and October 2014, and 1237 control participants. Intakes of dairy foods were queried with a self-administered food-frequency questionnaire and grouped into monthly intakes of total dairy, milk, yogurt, low-fat cheese, other cheese, and sweet dairy. ORs and 95% CIs were estimated with unconditional logistic regression adjusting for age, race, body mass index, menopausal status, energy intake, type of milk usually consumed, cigarette smoking status, and family history of breast cancer. Results: Total dairy intakes were associated with a non-significant 15% reduction in breast cancer risk (P = 0.11). Higher intakes of yogurt were associated with reduced risk of breast cancer (OR: 0.61; 95% CI: 0.46, 0.82) and higher intakes of American, cheddar, and cream cheeses were associated with a marginally significant increased risk (OR: 1.53; 95% CI: 0.99, 2.34; P = 0.05). Associations with dairy foods were mixed when stratified by estrogen receptor (ER) status, and in general reflected those of overall breast cancer. However, we observed positive associations between milk intake and risk of ER- breast cancer (OR: 1.58; 95% CI: 1.05, 2.37) and inverse associations between sweet dairy and ER+ breast cancer (OR: 0.52; 95% CI: 0.29, 0.95). Conclusions: Specific dairy foods may contribute to breast cancer risk in women, although the risk varies by source of dairy. Future studies are warranted to confirm the protective potential of yogurt in this type of cancer.
Keywords: breast cancer; cancer; cancer epidemiology; dairy; dietary intake; dietary patterns; estrogen receptor.