Dairy consumption and risk of breast cancer: a meta-analysis of prospective cohort studies.

Epidemiologic findings are inconsistent regarding risk for breast cancer related to dairy consumption. We performed a meta-analysis of prospective cohort studies to examine the association between diary product consumption and risk of breast cancer. A PubMed database search through January 2011 was performed for relevant studies. We included prospective cohort studies that reported relative risks with 95% confidence intervals for the association of dairy consumption and breast cancer risk. A random effects model was used to calculate the summary risk estimates. We identified 18 prospective cohort studies eligible for analysis, involving 24,187 cases and 1,063,471 participants. The summary relative risk of breast cancer for the highest intake of total dairy food compared with the lowest was 0.85 (95% confidence interval: 0.76-0.95), with evidence of heterogeneity (P = 0.01, I (2) = 54.5%). For milk consumption, the summary relative risk was 0.91 (95% confidence interval: 0.80-1.02), and substantial heterogeneity was observed (P = 0.003, I (2) = 59.7%). Subgroup analyses based on limited numbers of studies suggested that the associations were somewhat stronger for low-fat dairy intake than for high-fat dairy intake and for premenopausal women than for postmenopausal women. There was a significant dose-response relationship of total dairy food, but not milk, consumption with breast cancer risk. Little evidence of publication bias was observed. In conclusion, findings of the present meta-analysis indicate that increased consumption of total dairy food, but not milk, may be associated with a reduced risk of breast cancer.