Vitamin D concentrations and breast cancer incidence among Black/African American and non‐Black Hispanic/Latina women

Background Vitamin D may protect against breast cancer. Although Black/African American women and Hispanic/Latina women have lower circulating vitamin D levels than non‐Hispanic White women, few studies have examined the association between vitamin D and breast cancer within these racial/ethnic groups. Methods The vitamin D–breast cancer association was evaluated using a case‐cohort sample of self‐identified Black/African American and non‐Black Hispanic/Latina women participating in the US‐wide Sister Study cohort. Circulating 25‐hydroxyvitamin D (25(OH)D) and 24,25‐dihydroxyvitamin D (24,25(OH)2D) were measured using liquid chromatography‐tandem mass spectrometry in blood samples collected at the baseline from 415 women (290 Black/African American women and 125 non‐Black Hispanic/Latina women) who developed breast cancer. These were compared to concentrations in 1545 women (1084 Black/African American women and 461 Hispanic/Latina women) randomly selected from the cohort. Multivariable‐adjusted Cox regression was used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs). Results Over a mean follow‐up of 9.2 years, women with circulating 25(OH)D concentrations above the clinical cut point for deficiency (20.0 ng/mL) had lower breast cancer rates than women with concentrations ≤ 20 ng/mL (HR, 0.79; 95% CI, 0.61‐1.02). The inverse association was strongest among Hispanic/Latina women (HR, 0.52; 95% CI, 0.29‐0.93), with a weaker association observed among Black/African American women (HR, 0.89; 95% CI, 0.68‐1.18; P for heterogeneity = 0.13). There were no clear differences by menopausal status, follow‐up time, estrogen receptor status, or invasiveness. Neither 24,25(OH) 2 D nor the 24,25(OH) 2 D to 25(OH)D ratio were independently associated with breast cancer risk. Conclusions This prospective study supports the hypothesis that vitamin D may be protective against breast cancer incidence in women, including non‐Black Hispanic/Latina and Black/African American women. LAY SUMMARY Vitamin D may protect against breast cancer. Although women of color have lower average vitamin D levels than non‐Hispanic White women, few studies have considered the role of race/ethnicity. In a sample of self‐identified Black/African American and Hispanic/Latina women, we observed that vitamin D concentrations measured in blood were inversely associated with breast cancer, particularly among Latinas. These findings indicate that vitamin D may protect women against breast cancer, including those in racial/ethnic groups with low average circulating levels.