Racial differences in the relationship between vitamin D, bone mineral density, and parathyroid hormone in the National Health and Nutrition Examination Survey.

UNLABELLED: It is unclear whether optimal levels of 25-hydroxyvitamin D (25(OH)D) in whites are the same as in minorities. In adult participants of NHANES, the relationships between 25(OH)D, bone mineral density (BMD), and parathyroid hormone (PTH) differed in blacks as compared to whites and Mexican-Americans, suggesting that optimal 25(OH)D levels for bone and mineral metabolism may differ by race. INTRODUCTION: Blacks and Hispanics have lower 25-hydroxyvitamin D concentrations than whites. However, it is unclear whether 25(OH)D levels considered "optimal" for bone and mineral metabolism in whites are the same as those in minority populations. METHODS: We examined the relationships between 25(OH)D and parathyroid hormone in 8,415 adult participants (25% black and 24% Mexican-American) in the National Health and Nutrition Examination Surveys 2003-2004 and 2005-2006; and between 25(OH)D and bone mineral density in 4,206 adult participants (24% black and 24% Mexican-American) in the 2003-2004 sample. RESULTS: Blacks and Mexican-Americans had significantly lower 25(OH)D and higher PTH concentrations than whites (P < 0.01 for both). BMD significantly decreased (P < 0.01) as serum 25(OH)D and calcium intake declined among whites and Mexican-Americans, but not among blacks (P = 0.2). The impact of vitamin D deficiency (25(OH)D ≤ 20 ng/ml) on PTH levels was modified by race/ethnicity (P for interaction, 0.001). Whereas inverse relationships between 25(OH)D and PTH were observed above and below a 25(OH)D level of 20 ng/ml in whites and Mexican-Americans, an inverse association between 25(OH)D and PTH was only observed below this threshold in blacks, with the slope of the relationship being essentially flat (P = 0.7) above this cut-point, suggesting that PTH may be maximally suppressed at lower 25(OH)D levels in blacks than in whites or Mexican-Americans. CONCLUSIONS: The relationships between 25(OH)D, BMD, and PTH may differ by race among US adults. Whether race-specific ranges of optimal vitamin D are needed to appropriately evaluate the adequacy of vitamin D stores in minorities requires further study.

Race is a major determinant of secondary hyperparathyroidism in uremic patients: comparative study of Blacks and Hispanics.

BACKGROUND: Racial differences in bone and mineral metabolism are characterized by higher circulating intact parathyroid hormone levels (iPTH) in Black vs. White patients with end-stage renal disease (ESRD). The susceptibility of Hispanic patients to secondary hyperparathyroidism is not known. METHOD: This is a cross-sectional study that compares bone and mineral parameters of 48 Black and 61 Hispanic ESRD patients attending a single outpatient hemodialysis center. RESULT: The mean iPTH level was significantly higher in Blacks vs. Hispanics, despite similar levels of serum bone-specific alkaline phosphatase (BSAP), calcium, phosphorus and similar dosages of vitamin D analogs. After adjusting for independent variables including age, diabetic status and plasma levels of C-reactive protein, phosphorus and albumin significant predictors of iPTH were race (p < 0.01), gender (p < 0.05), serum calcium (p < 0.05), BSAP (p < 0.0001) and doses of vitamin D analogs (p < 0.001). Adjusted predictors of serum BSAP were PTH (p < 0.0001), gender (p = 0.01) and serum albumin (p < 0.005), but not race. There was no significant difference in serum BSAP between Blacks and Hispanics despite 60% higher iPTH levels in Blacks. CONCLUSIONS: Amongst ESRD patients, Blacks have higher iPTH levels compared with Hispanics despite similar BSAP levels, these finding support the emerging evidence of racial/ethnic differences in response of bone to PTH action.