SAT-536 Vitamin D Status in an Ambulatory Cohort of Women undergoing Screening Mammography

Abstract

INTRODUCTION: Controversy exists over possible ethnic differences in 25-OH-vitamin D (25OHD) levels among healthy individuals, such as blacks having lower levels than whites. The extent to which these possible differences reflect physiologic deficiency is unclear. We utilized data from women undergoing routine mammography and measures of mineral metabolism to examine 25OHD levels and its relationship to parathyroid hormone (PTH) levels by race/ethnicity. METHODS: Data were obtained from an observational cohort study examining breast arterial calcification in women aged 60-79 years where laboratory measures also included calcium, PTH, 25OHD, and creatinine to estimate glomerular filtration rate (eGFR). For this study, we identified women without hypercalcemia (Ca >10.3) and free of chronic kidney disease (eGFR<60). Analyses included the distribution of 25OHD level and whether low 25OHD was associated with higher PTH. Sensitivity analyses were conducted excluding those with use of calcium (>3x/week) or vitamin D (>1x/week) supplements because of the potential impact of supplement use on 25OHD level. RESULTS: Among 3544 women (62.2% white, 11.0% black, 10.0% Hispanic, 15.4% Asian, 1.4% other/unknown), 25OHD varied by race/ethnicity, with mean ± SD and median (interquartile range, IQR) values as follows: white 37.5 ± 12.7 and 36 (IQR 30-44); black 29.8 ± 12.7 and 30 (IQR 20-38); Hispanic 32.1 ± 11.5 and 30 (24-39); and Asian 35.0 ± 12.0 and 34 (27-42) ng/mL. The proportion of women with 25OHD <20 ng/mL also varied by race/ethnicity: white (5.4%), black (24.0%), Hispanic (11.6%) and Asian (7.9%). The median PTH level for these same subgroups with low 25OHD level were: white 46 (IQR 34-63), black 62 (46-79), Hispanic 43 (30-61), and Asian 41 (36-59) pg/mL (p<0.01 for black vs each of the other race/ethnicities). When restricted to the 1277 women without regular use of calcium or vitamin D supplements, (57.7% white, 15.1% black, 11.9% Hispanic, 13.5% Asian, 1.8% other/unknown), 25OHD mean ± SD and median (IQR) values were somewhat lower: white 30.5 ± 10.1 and 30 (IQR 24-36); black 24.0 ± 10.8; 23 (IQR 15-31), Hispanic 25.8 ± 9.3 and 25 (19-31); and Asian 27.0 ± 9.5 and 26 (20-33) ng/mL. Among these 1277 women, the proportions with 25OHD <20 ng/mL were: white (13.4%), black (39.4%), Hispanic (25.7%) and Asian (22.7%). The median PTH level for these subgroups with low 25OHD level were: white 45 (IQR 33-61), black 61 (45-81), Hispanic 43 (30-61) and Asian 41 (38-60) pg/mL (p<0.01 for black vs each of the other race/ethnicities). CONCLUSIONS: Compared to white women, black and Hispanic women have about 20% lower 25OHD levels. Compared to white, black women also have significantly higher PTH (about one-third higher) when 25OHD is low. We hypothesize that in black women (with lower 25OHD level), PTH elevation maintains adequate mineral balance and may contribute to their greater skeletal mass.