The association between dairy intake and breast cancer risk has not been well investigated, especially in the Chinese population. This study aimed to examine the association between the weekly frequency of dairy intake and the risk of breast cancer among women in Northern and Eastern China, and to investigate whether the association varied by hormone receptor status. A total of 1,286 cases of breast cancer and 1,461 controls were enrolled in this study. Dairy intake was obtained using a food-frequency questionnaire (FFQ). Frequency of dairy intake per week was divided into four categories (<1 day/week, 1-2 days/week, 3-4 days/week and 5-7 days/week). Unconditional multivariate logistic regression analysis was used to estimate odds ratios (ORs) and 95% confidence intervals (95% CI). Stratified analyses were performed by residence, age, and education level. Separate analyses were also conducted for different estrogen receptor (ER) and progesterone receptor (PR) status. This analysis revealed that weekly frequency of dairy intake was strongly inversely associated with breast cancer risk, with an adjusted OR for intake 5-7 days/week of 0.53 (95% CI=0.39-0.72, P<0.001 for trend). In the stratified analyses, women who consumed dairy 5-7 days/week had a lower risk of breast cancer in urban areas (OR=0.45, 95% CI=0.30-0.66, P<0.001 for trend), in the group 45-59 years old (OR=0.39, 95% CI=0.26-0.60, P<0.001 for trend), and in the group educated to senior high school or above (OR=0.39, 95% CI=0.25-0.59, P<0.001 for trend). There was an inverse association between the weekly frequency of dairy intake and the risk of ER⁺, PR⁺, and ER⁺PR⁺ breast cancer (all P<0.001 for trend). These results indicated that the weekly frequency of dairy intake was inversely associated with the risk of breast cancer among women in Northern and Eastern China.

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