Defining physiologically “normal” vitamin D in African Americans
- 305 Downloads
The relationship between serum 25(OH)D and intact parathyroid hormone (iPTH) was evaluated in the Multicenter Osteoarthritis Study (MOST). No further change in iPTH was observed for African Americans with 25(OH)D levels above 20 ng/ml, suggesting that compared to Caucasians, lower vitamin D targets for sufficiency may be appropriate for African Americans.
Vitamin D levels ≥30 ng/ml are commonly considered “normal” based upon maximal suppression of iPTH; however, this has recently been challenged and the optimal 25(OH)D level among non-Caucasians is unclear. We evaluated the cross-sectional relationship between serum 25(OH)D and iPTH in a sample of Caucasian and African American adults.
We used baseline serum samples of participants from the Multicenter Osteoarthritis Study (MOST) for this analysis and used three methods to model the relationship between 25(OH)D and iPTH: ordinary least squares regression (OLS), segmented regression and Helmert contrasts.
Among Caucasians (n = 1,258), 25(OH)D and iPTH ranged from 4 to 51 ng/ml and 2 to 120 pg/ml and from 3 to 32 ng/ml and 3 to 119 pg/ml in African Americans (n = 423). We observed different thresholds between African Americans and Caucasians using each analytic technique. Using 25(OH)D as a categorical variable in OLS, iPTH was statistically higher at lower 25(OH)D categories than the 24–32 ng/ml referent group among Caucasians. However, in African Americans, the mean iPTH was only significantly higher at 25(OH)D levels below 15 ng/ml. Using segmented regression, iPTH appeared to stabilize at a lower 25(OH)D level in African Americans (19–23 ng/ml) compared to in Caucasians (>32 ng/ml). Helmert contrasts also revealed a lower threshold in African Americans than Caucasians.
Among MOST participants, the 25(OH)D thresholds at which no further change in iPTH was observed was approximately 20 ng/ml in African Americans versus approximately 30 ng/ml in Caucasians, suggesting optimal vitamin D levels in Caucasians may not be applicable to African Americans.
KeywordsAfrican American Osteoporosis Parathyroid hormone Racial differences Thresholds Vitamin D
The MOST study is funded by the following grants from the National Institutes of Health: Boston University (David Felson, MD—1 U01 AG18820), University of Iowa (James Torner, PhD—1 U01 AG18832), University of Alabama at Birmingham (Cora E. Lewis, MD MSPH—1 U01 AG18947) and University of California San Francisco (Michael Nevitt, PhD—1 U01 AG19069). Assays for vitamin D and iPTH were supported, in part, by a research grant from the Investigator-Initiated Studies Program of Merck & Co., Inc to JRC. Dr. Curtis receives support from the NIH (AR053351) and AHRQ (R01HS018517). Dr. Neogi is supported by 5K23AR055127.
Conflicts of interest
- 8.Osteoporosis WSGotPaMo (2003) Prevention and managment of osteoporosis: report of a WHO scientific group. GenevaGoogle Scholar
- 12.Nesby-O'Dell S, Scanlon KS, Cogswell ME, Gillespie C, Hollis BW, Looker AC, Allen C, Doughertly C, Gunter EW, Bowman BA (2002) Hypovitaminosis D prevalence and determinants among African American and White women of reproductive age: third National Health and Nutrition Examination Survey, 1988–1994. Am J Clin Nutr 76(1):187–192PubMedGoogle Scholar
- 16.Gutierrez OM, Farwell WR, Kermah D, Taylor EN (2010) Racial differences in the relationship between vitamin D, bone mineral density, and parathyroid hormone in the National Health and Nutrition Examination Survey. Osteoporos Int. doi: 10.1007/s00198-010-1383-2
- 17.Ross CATC, Yaktine AK, Del Valle HB (eds) (2011) Dietary reference intakes for calcium and vitamin D. The National Academies Press, Washington, DCGoogle Scholar
- 18.Vitamin D, 25-Hydroxy. Laboratory Corporation of America Holdings and Lexi-Comp Inc. https://www.labcorp.com/wps/portal/!ut/p/c1/04_SB8K8xLLM9MSSzPy8xBz9CP0os_hACzO_QCM_IwMLXyM3AyNjMycDU2dXQwN3M6B8JG55AwMCuv088nNT9SP1o8zjQ11Ngg09LY0N_N2DjQw8g439TfyM_MzMLAz0Q_QjXYCKIvEqKsiNKDfUDVQEAAzyjqE!/dl2/d1/L0lJWXBwZyEhL3dIRUJGUUFnc2FBRUJyQ0svWUk1eWx3ISEvN19VRTRTMUk5MzBPR1MyMElTM080TjJONjY4MC92aWV3VGVzdA!!/?testId = 408405. Accessed August 24, 2011 2011Google Scholar
- 19.Dawson-Hughes B (2011) Msculoskeletal health and the cutoff of 30. Paper presented at the American Society for Bone and Mineral Research, San Diego, CAGoogle Scholar
- 29.Kleerekoper M, Nelson DA, Peterson EL, Flynn MJ, Pawluszka AS, Jacobsen G, Wilson P (1994) Reference data for bone mass, calciotropic hormones, and biochemical markers of bone remodeling in older (55–75) postmenopausal White and Black women. J Bone Miner Res 9(8):1267–1276PubMedCrossRefGoogle Scholar