Association between calcium intake and risk of breast cancer: An updated systematic review and dose-response meta-analysis of cohort studies.

Background: Prospective cohort studies that dietary or total calcium intake was considered as the exposure variable and risk of BC as the main or second outcome were included in this systematic review.

Methods: We searched the online databases of PubMed, Web of science, Scopus and, Google scholar for relevant studies published up to November 2021, using relevant keywords. Seven cohort studies including 1,579,904 participants, were eligible for the current meta-analysis.

Results: Pooled effect size for the highest versus lowest category indicated that increasing dietary calcium intake was significantly associated with a reduced risk of BC (RR, 0.90; 95% CI: 0.81-1.00). However, total calcium intake revealed a non-significant inverse association (RR, 0.97; 95%CI, 0.91-1.03). Dose-response meta-analysis showed that every additional 350 mg per day dietary (RR, 0.94; 95% CI, 0.89-0.99) and total calcium intake (RR, 0.99; 95% CI, 0.97-1.00) was significantly associated with a lower risk of BC. Also, a significant decreasing trend for the risk of BC was observed after 500 mg/d of dietary calcium intake (P-nonlinearity = 0.05, n = 6.

Conclusion: Finally, our dose-response meta-analysis revealed a 6 and 1% lower risk of BC in each 350 mg per day increment in dietary and total calcium intake, respectively.