Dietary calcium, vitamin D, and breast cancer risk in women: findings from the SUN cohort

Epidemiological evidence concerning the relationship between calcium and vitamin D intake and breast cancer (BC) is inconclusive. Moreover, the association according to menopausal status remains unclear. We aimed to assess whether total intakes from dietary and supplemental sources of calcium and vitamin D were associated with the incidence of BC in a Mediterranean cohort. We prospectively evaluated the association between intakes of calcium and vitamin D and BC risk among 10,812 women in the Seguimiento Universidad de Navarra (SUN) Project, a Spanish cohort of university graduates. During a mean follow-up of 10.7 years, 101 incident BC cases were confirmed. Evidence of a non-linear association between total calcium intake and BC risk was found (Pnon-linearity = 0.011) with risk reductions associated with higher intake up to approximately 1400 mg/day. Moderate intake [Tertile 2 (T2)] of total calcium was associated with lower overall BC risk [HR for T2 vs. Tertile 1 (T1): 0.55; 95% CI 0.33–0.91] and also among postmenopausal women (HRT2 vs. T1 = 0.38; 95% CI 0.16–0.92). Intake of vitamin D was not associated with BC risk. Our findings suggest an L-shaped association between total calcium intake and BC incidence. Moderate calcium intake may be associated with lower BC risk among overall and postmenopausal women, but not among premenopausal women. No evidence for any association between vitamin D intake and BC was found. Adherence to current guidelines recommendations for calcium intake may help to reduce BC risk.