Abstract C046: Dietary calcium and vitamin D and sun exposure with the risk of breast cancer among African American women
Authors: Qin Bo , Xu Baichen , Ji Nan , Pawlish Karen , Yao Song , Ambrosone Christine , Demissie Kitaw , Hong Chi-Chen , Bandera Elisa V. 
Published: August 2020

Background: Compared to European American women, African American (AA) women have a higher incidence of breast cancer (BrCa) under age 45, and are more likely to develop estrogen receptor-negative (ER-) tumors, a more aggressive BrCa subtype. Experimental studies drew attention to the potential antitumorigenic properties of calcium and vitamin D. Darker skin color reduces the cutaneous synthesis of vitamin D upon sun exposure. This, together with the tendency of AAs to consume less vitamin D and calcium from food and supplement sources, places AAs at risk for vitamin D and calcium deficiency. However, data are limited regarding the impact of calcium and vitamin D on risk of BrCa and specific subtypes among AA women.

Objective: To evaluate calcium intake and vitamin D exposure (through food, supplements and sunlight) with the risk of BrCa and its subtypes among AA women.

Methods: We evaluated these associations among 1033 BrCa cases and 391 controls of AA descent recruited since March 2012 in the Women's Circle of Health Study. Cases were identified by rapid case ascertainment in 10 counties in New Jersey. Controls were identified by random-digit-dialing and community-based recruitment, and were frequency matched by age group and county of residence. Dietary information over the year prior to diagnosis (for cases) or the reference date (for controls) was assessed via a validated food frequency questionnaire through in-person interviews. Supplemental intakes including multivitamin sources and daily hours spent outdoors in daylight were also collected. Hormone receptor status was obtained from pathology reports. Multivariable logistic regression models were used to estimate odds ratios (ORs) and 95% confidence intervals (CIs) adjusting for relevant sociodemographic, reproductive, and lifestyle risk factors.

Results: Vitamin D intake from food was not associated with BrCa risk. However, for supplemental vitamin D intake, we observed a significant decreased overall BrCa risk for users of ≤800 IU/day vs. nonusers (OR=0.73, 95% CI: 0.54, 0.98), which was limited to estrogen receptor-positive (ER+) BrCa (OR=0.69, 95% CI: 0.50, 0.94), but not for ER- or triple-negative BrCa. More daylight hours spent outdoors in a year predicted a lower risk of pre- and postmenopausal BrCa [comparing the highest quartile (Q4) vs. lowest (Q1): OR=0.37, 95% CI: 0.20-0.68, p-trend: 0.002; OR=0.46, 95% CI: 0.30-0.71, p-trend: 0.001, respectively]. The significant inverse associations were observed for both ER+ and ER- BrCa, but not for triple-negative BrCa. Calcium intake was not associated with BrCa risk.

Conclusion: Our findings suggest that moderate intake of supplemental vitamin D may decrease the risk of ER+ BrCa. Sun exposure may decrease the risk of BrCa among AA women, which does not appear to differ by menopausal status and ER status.

Citation Format: Bo Qin, Baichen Xu, Nan Ji, Karen Pawlish, Song Yao, Christine Ambrosone, Kitaw Demissie, Chi-Chen Hong, Elisa V. Bandera. Dietary calcium and vitamin D and sun exposure with the risk of breast cancer among African American women [abstract]. In: Proceedings of the Eleventh AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2018 Nov 2-5; New Orleans, LA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2020;29(6 Suppl):Abstract nr C046.