PurposeTo date, studies investigating the association between dairy consumption and breast cancer in women have produced conflicting results. As diet is an important, modifiable factor affecting cancer development, the aim of this study was to examine the association between dairy consumption and breast cancer risk.MethodsPubMed, Embase, and Cochrane Library databases were searched with a priority for prospective cohort studies. Case-control studies were also considered in case of the absence of a cohort study.ResultsWe analyzed 22 prospective cohort studies (1,566,940 participants) and five case-control studies (33,372 participants). High and modest dairy consumption (>600 and 400-600 g/day, respectively) significantly reduced the risk of breast cancer compared with low dairy consumption (<400 g/day; risk ratio [RR], 0.90, 95% confidence interval [CI], 0.83-0.98, and RR, 0.94, 95% CI, 0.91-0.98, respectively). A significant linear relationship between dairy consumption and breast cancer risk was found on dose-response analysis. Subgroup analysis found that yogurt (RR, 0.91; 95% CI, 0.83-0.99) and low-fat dairy (RR, 0.85; 95% CI, 0.75-0.96) reduced the risk of breast cancer, while other dairy product types did not. A reduced risk was observed for people in the United States (RR, 0.91; 95% CI, 0.83-0.99) and in those followed for ≥10 years (RR, 0.90; 95% CI, 0.81-0.99). Additionally, the highest level of dairy consumption among Asians was associated with a reduced risk of breast cancer (odds ratio, 0.74; 95% CI, 0.62-0.88).ConclusionDairy consumption was inversely associated with the risk of developing breast cancer and this effect was dependent on the dose, dairy-type, and time.
