Background: Epidemiologic studies examining the relations between dairy product and calcium intakes and breast cancer have been inconclusive, especially for tumor subtypes. Objective: To evaluate the associations between intakes of specific dairy products and calcium and risk of breast cancer overall and for subtypes defined by estrogen receptor (ER) status. Method: We pooled the individual-level data of over 1 million women who were followed for a maximum of 8-20 years across studies. Associations were evaluated for dairy product and calcium intakes and risk of incident invasive breast cancer overall (n = 37,861 cases) and by subtypes defined by ER status. Study-specific multivariable hazard ratios (HRs) were estimated and then combined using random-effects models. Results: Overall, no clear association was observed between the consumption of specific dairy foods, dietary (from foods only) calcium, and total (from foods and supplements) calcium, and risk of overall breast cancer. Although each dairy product showed a null or very weak inverse association with risk of overall breast cancer (P, test for trend >0.05 for all), differences by ER status were suggested for yogurt and cottage/ricotta cheese with associations observed for ER-negative tumors only (pooled HR = 0.90, 95% CI: 0.83, 0.98 comparing ≥60 g/d with <1 g/d of yogurt and 0.85, 95% CI: 0.76, 0.95 comparing ≥25 g/d with <1 g/d of cottage/ricotta cheese). Dietary calcium intake was only weakly associated with breast cancer risk (pooled HR = 0.98, 95% CI: 0.97, 0.99 per 350 mg/d). Conclusion: Our study shows that adult dairy or calcium consumption is unlikely to associate with a higher risk of breast cancer and that higher yogurt and cottage/ricotta cheese intakes were inversely associated with the risk of ER-negative breast cancer, a less hormonally dependent subtype with poor prognosis. Future studies on fermented dairy products, earlier life exposures, ER-negative breast cancer, and different racial/ethnic populations may further elucidate the relation.
Bibliographical noteFunding Information:
The centralization, checking, harmonization, and statistical analyses of the participant-level data from each of the cohorts were supported by NIH (grant CA55075 to WCW) and the Breast Cancer Research Foundation (to WCW). YW was supported by the China Scholarship Council, the Muriel K. and David R. Pokross and Joan P. and Ronald C. Curhan Doctoral Student Support Fund in Nutrition, and the Mayer Fund. For each cohort, funding, acknowledgements, and disclaimers are listed in Supplemental Table 10. The funders did not have any role in the design, implementation, analysis, or interpretation of the data. The Pooling Project of Prospective Studies of Diet and Cancer is a project within the National Cancer Institute Cohort Consortium.
© The Author(s) 2021. Published by Oxford University Press on behalf of the American Society for Nutrition.
- breast cancer
- dairy products
- pooled analysis