Dietary Intake of Calcium, Magnesium and Risk of Breast Cancer

Objective: Magnesium (Mg) is the second most abundant intracellular cation in the body, and is essential for DNA synthesis and repair, and associated with DNA mutations leading to carcinogenesis. Calcium (Ca) plays an important role in various cellular activities including cell proliferation, differentiation, and apoptosis. Magnesium and calcium antagonizes each other in (re)absorption, cell cycle regulation, inflammation and many other physiologic activities. However, results on the relationships between dietary intake of magnesium and calcium remain mixed, and few studies have evaluated the interaction between calcium and magnesium intake on breast cancer incidence. We aim to test whether the associations of breast cancer risk with intakes of calcium and magnesium differ by the dietary Ca to Mg intake ratio. Materials and Methods: The Swedish Women’s Lifestyle and Health Cohort Study included 49,259 women in Sweden who were aged 30-50 years between 1991 to 1992. Complete follow-up for breast cancer incidence was performed until December, 2012 through linkage to national registries. Cox proportional hazard regression models were used to estimate hazard ratios (HR) and 95% confidence intervals (95% CI) for breast cancer risk. Results: During follow-up, 1909 primary, incident breast cancer cases were diagnosed. After adjusting for known risk factors of breast cancer, intakes of energy, vitamin D, magnesium, higher dietary intake of calcium was associated with reduced breast cancer risk (HR: 0.98; 95%CI: 0.98-0.99 for highest versus lowest quartile; p trend = 0.01), and dietary intake of vitamin D was also associated with reduced breast cancer risk (HR: 0.46; 95%CI:0.25,0.86) for highest versus lowest quartile. Conclusions: In this preliminary analysis, we found that dietary calcium and vitamin D intake may be protective factors of breast cancer for women.