ASPO Abstracts
Intakes of calcium and vitamin D, sun exposure, and breast cancer subtypes among African American women
Category: Cancer Health Disparities
Conference Year: 2019
Abstract Body:
Background: Darker skin complexion reduces cutaneous synthesis of vitamin D upon sun exposure. This, along with the tendency of African Americans (AAs) to consume less vitamin D and calcium, puts AAs at risk for vitamin D and calcium deficiency. However, data are limited on the associations of these factors with breast cancer (BrCa) subtypes among AA women, who have a disproportionately high incidence of estrogen receptor negative (ER-) BrCa. This study aimed to evaluate the impact of calcium intake and vitamin D exposure (through food, supplements and sunlight) on the risk of BrCa subtypes among AA women.Methods: We evaluated these associations among AA BrCa cases and controls (1,724 and 1,233, respectively) in the Women’s Circle of Health Study (WCHS) and the Women’s Circle of Health Follow-Up Study (WCHFS). Cases were identified via rapid case ascertainment in metropolitan New York City and New Jersey, and controls via random-digit-dialing and community-based recruitment. Multivariable polytomous logistic regressions were used to estimate odds ratios (ORs) and 95% confidence intervals (CIs) of ER+ and ER- BrCa vs. controls, and multivariable logistic regressions for triple negative (TN) BrCa. The ORs from each study were pooled to obtain a summary estimate using an inverse variance-weighted random-effects model. Results: Calcium or vitamin D intake from food was not associated with risk of BrCa subtypes in the pooled analysis. For supplemental vitamin D intake, which was collected in WCHFS only, intake of ≤800 IU/day (vs. non-users) was associated with decreased risk of ER+ BrCa (OR=0.68, 95% CI: 0.50-0.94) and TN BrCa (OR=0.54, 95% CI: 0.33-0.89); intake of >800 IU/day was not associated with risk of BrCa subtypes. More daylight hours spent outdoors in a year predicted lower risk of ER+, ER- and TN BrCa [comparing highest vs. lowest quartile: OR=0.43, 95% CI: 0.29-0.61, p-trend: <0.001; OR=0.43, 95% CI: 0.27-0.68, p-trend: <0.001; OR=0.52, 95% CI: 0.30-0.91, p-trend: 0.02, respectively]. Conclusions: Our findings suggest that a moderate intake of supplemental vitamin D may decrease ER+ and TN BrCa risk and more sun exposure may decrease BrCa risk among AA women, including more aggressive subtypes, ER- and TN BrCa.
Keywords: Breast cancer risk, vitamin D, sun exposure, African American