title: Vitamin D status of black and white Americans and changes in vitamin D metabolites after varied doses of vitamin D supplementation.
abstract: BACKGROUND
  Controversy exists over the disparate circulating 25-hydroxyvitamin D [25(OH)D] concentrations between black and white Americans.
  
  
  OBJECTIVE
  We sought to determine whether there are differences in total and directly measured free 25(OH)D concentrations between black and white American adults and how daily supplementation with cholecalciferol changes these concentrations.
  
  
  METHODS
  Cross-sectional and longitudinal analyses were conducted with the use of data from 2 placebo-controlled, randomized trials at 2 academic medical centers in the United States: CaDDM (Calcium and Vitamin D in Type 2 Diabetes) and DDM2 (Vitamin D for Established Type 2 Diabetes). A total of 208 subjects with pre- or well-controlled diabetes with a mean age of 59.1 y and mean body mass index (BMI; in kg/m(2)) of 31.6 were randomly assigned to receive daily cholecalciferol supplementation at 1 of 2 doses (2000 or 4000 IU) or a matching placebo for 16 wk. We measured serum total 25(OH)D, vitamin D-binding protein (DBP) by 2 different immunoassays (with the use of monoclonal or polyclonal antibodies), parathyroid hormone, and albumin. Free 25(OH)D concentration was directly measured and calculated.
  
  
  RESULTS
  Blacks had lower total 25(OH)D concentrations than whites [adjusted median: 20.3 ng/mL (95% CI: 16.2, 24.5 ng/mL) compared with 26.7 ng/mL (95% CI: 25.2, 28.1 ng/mL), respectively; P = 0.026)], and a higher proportion of blacks had total 25(OH)D concentrations <20 ng/mL (46% compared with 19%, respectively; P < 0.001). Directly measured free 25(OH)D concentrations were lower in blacks than in whites [adjusted median: 4.5 ng/mL (95% CI: 3.7, 5.4 ng/mL) compared with 5.7 ng/mL (95% CI: 5.4, 5.9 ng/mL), respectively; P = 0.044] and were strongly correlated with total 25(OH)D without an effect of race. DBP was lower in blacks when measured by the monoclonal but not the polyclonal antibody immunoassay. Cholecalciferol supplementation increased total and measured free 25(OH)D concentrations proportionally to the dose and without a difference between races.
  
  
  CONCLUSIONS
  The relation between free and total 25(OH)D did not vary systematically by race in this multiracial population with pre- or well-controlled diabetes. The results need to be replicated in additional cohorts before concluding that the clinical assessment of vitamin D status in blacks and whites should follow a single standard. The CaDDM and DDM2 trials were registered at clinicaltrials.gov as NCT00436475 and NCT01736865, respectively.
authors.affiliation: Division of Endocrinology, Diabetes and Metabolism, and College of Medicine, Department of Internal Medicine, Taibah University, Medina, Saudi Arabia;
authors.forename: Naweed S
authors.initials: NS
authors.lastname: Alzaman
authors.affiliation: Division of Endocrinology, Diabetes and Metabolism, and Bone Metabolism Laboratory, Jean Mayer USDA Human Nutrition Research Center on Aging, Tufts University, Boston, MA; and.
authors.forename: Bess
authors.initials: B
authors.lastname: Dawson-Hughes
authors.affiliation: Predictive Analytics and Comparative Effectiveness Center, Tufts Medical Center, Boston, MA;
authors.forename: Jason
authors.initials: J
authors.lastname: Nelson
authors.affiliation: Division of Endocrinology, Duke University Medical Center, Durham, NC.
authors.forename: David
authors.initials: D
authors.lastname: D'Alessio
authors.affiliation: Division of Endocrinology, Diabetes and Metabolism, and apittas@tuftsmedicalcenter.org.
authors.forename: Anastassios G
authors.initials: AG
authors.lastname: Pittas
mesh_terms: D001741:Black or African American; D000368:Aged; D015992:Body Mass Index; D002762:Cholecalciferol / Q000008:administration & dosage / Q000097:blood / Q000627:therapeutic use; D003430:Cross-Sectional Studies; D004268:DNA-Binding Proteins / Q000097:blood; D003924:Diabetes Mellitus, Type 2 / Q000097:blood / Q000208:ethnology; D019587:Dietary Supplements; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D014157:Transcription Factors / Q000097:blood; D014481:United States; D014807:Vitamin D / Q000008:administration & dosage / Q000031:analogs & derivatives / Q000097:blood* / Q000627:therapeutic use; D014808:Vitamin D Deficiency / Q000097:blood* / Q000188:drug therapy / Q000208:ethnology; D044465:White People
chemical_list: C063898:DBP protein, human; D004268:DNA-Binding Proteins; D014157:Transcription Factors; D014807:Vitamin D; D002762:Cholecalciferol; C104450:25-hydroxyvitamin D
keywords: African American; clinical trial; free vitamin D; supplementation; vitamin D; vitamin D-binding protein; white