title: Free 25(OH)D and the Vitamin D Paradox in African Americans.
abstract: BACKGROUND
  African Americans have a lower total serum 25-hydroxyvitamin D [25(OH)D] but superior bone health. This has been referred to as a paradox. A recent publication found that free serum 25(OH)D is the same in black and white individuals. However, the study was criticized because an indirect method was used to measure free 25(OH)D. A direct method has recently been developed.
  
  
  OBJECTIVE
  We hypothesized that although total serum 25(OH)D is lower in African Americans, free serum 25(OH)D measured directly would not differ between races.
  
  
  METHODS
  White and black healthy postmenopausal women were matched for age and body mass index. Serum total 25(OH)D, PTH, 1,25-dihydroxyvitamin D, vitamin D binding protein (VDBP), and bone density were measured. Measurement of free 25(OH)D was carried out using an ELISA.
  
  
  METHODS
  The study was conducted at an ambulatory research unit in a teaching hospital.
  
  
  RESULTS
  A cross-racial comparison of serum free 25(OH)D was performed.
  
  
  RESULTS
  A propensity match resulted in the selection of a total of 164 women. Total 25(OH)D was lower in black women (19.5 ± 4.7 vs 26.9 ± 6.4 ng/mL), but a direct measurement of free 25(OH)D revealed almost identical values (5.25 ± 1.2 vs 5.25 ± 1.3 ng/mL) between races. VDBP was significantly lower in blacks when using a monoclonal-based ELISA but higher with a polyclonal-based ELISA. Serum PTH, 1,25-dihydroxyvitamin D, and bone density were higher in African Americans.
  
  
  CONCLUSIONS
  Free serum 25(OH)D is the same across races despite the lower total serum 25(OH)D in black women. Results comparing VDBP between races using a monoclonal vs a polyclonal assay were discordant.
authors.affiliation: Winthrop University Hospital, Mineola, New York 11501.
authors.forename: John
authors.initials: J
authors.lastname: Aloia
authors.affiliation: Winthrop University Hospital, Mineola, New York 11501.
authors.forename: Mageda
authors.initials: M
authors.lastname: Mikhail
authors.affiliation: Winthrop University Hospital, Mineola, New York 11501.
authors.forename: Ruban
authors.initials: R
authors.lastname: Dhaliwal
authors.affiliation: Winthrop University Hospital, Mineola, New York 11501.
authors.forename: Albert
authors.initials: A
authors.lastname: Shieh
authors.affiliation: Winthrop University Hospital, Mineola, New York 11501.
authors.forename: Gianina
authors.initials: G
authors.lastname: Usera
authors.affiliation: Winthrop University Hospital, Mineola, New York 11501.
authors.forename: Alexandra
authors.initials: A
authors.lastname: Stolberg
authors.affiliation: Winthrop University Hospital, Mineola, New York 11501.
authors.forename: Louis
authors.initials: L
authors.lastname: Ragolia
authors.affiliation: Winthrop University Hospital, Mineola, New York 11501.
authors.forename: Shahidul
authors.initials: S
authors.lastname: Islam
mesh_terms: D001741:Black or African American; D000368:Aged; D015992:Body Mass Index; D015519:Bone Density / Q000502:physiology*; D005260:Female; D006801:Humans; D008875:Middle Aged; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000097:blood; D014808:Vitamin D Deficiency / Q000097:blood; D044465:White People
chemical_list: D014807:Vitamin D; C104450:25-hydroxyvitamin D