title: Dose and time responses of vitamin D biomarkers to monthly vitamin D3 supplementation in overweight/obese African Americans with suboptimal vitamin d status: a placebo controlled randomized clinical trial.
abstract: BACKGROUND
  A critical need exists to better understand the physiological sequel of vitamin D supplementation in obese individuals and African Americans. The aim was to comprehensively evaluate dose- and time-responses of a panel of vitamin D biomarkers to vitamin D supplements in this population.
  
  
  METHODS
  We conducted a 16-week randomized, double-blinded, and placebo-controlled clinical trial. Seventy overweight/obese African Americans (age 13-45 years, 84 % females) with 25-hydroxyvitamin D [25(OH)D] concentrations ≤20 ng/mL were randomly assigned to receive a supervised monthly oral vitamin D3 of 18,000 IU (~600 IU/day, n = 17), 60,000 IU (~2000 IU/day, n = 18), 120,000 IU (~4000 IU/day, n = 18), or placebo (n = 17).
  
  
  RESULTS
  There were significant dose- and time-responses of circulating 25(OH)D, 1,25-dihydroxyvitamin D [1,25(OH)2D], and intact parathyroid hormone (iPTH), but not fibroblast growth factor-23 (FGF-23), phosphorus and urine calcium to the vitamin D supplements. The mean 25(OH)D concentrations in the 2000 IU and 4000 IU groups reached ≥30 ng/mL as early as 8-weeks and remained at similar level at 16-weeks. The increase of 25(OH)D was significantly higher in the 4000 IU group than all the other groups at 8-weeks. The increase of 1,25(OH)2D was significantly higher in the 2000 IU and 4000 IU groups than the placebo at 8-weeks. Only the 4000 IU compared to the placebo significantly reduced iPTH at 8- and 16-weeks.
  
  
  CONCLUSIONS
  Our RCT, for the first time, comprehensively evaluated time- and dose- responses of vitamin D supplementation in overweight/obese African Americans with suboptimal vitamin D status. Circulating 25(OH)D, 1,25(OH)2D, and iPTH, but not FGF-23, phosphorus and urine calcium, respond to vitamin D supplementation in a time- and dose-response manner. By monthly dosing, 2000 IU appears to be sufficient in achieving a 25(OH)D level of 30 ng/mL in this population. However, importantly, 4000 IU, rather than 2000 IU, seems to suppress iPTH. If replicated, these data might be informative in optimizing vitamin D status and providing individualized dosing recommendation in overweight/obese African Americans.
  
  
  BACKGROUND
  ClinicalTrials.gov number: NCT01583621, Registered on April 3, 2012.
authors.affiliation: Georgia Prevention Institute, Medical College of Georgia, Georgia Regents University, Building HS-1640, Augusta, 30912-3715 GA USA ; Department of Internal Medicine, Medical College of Georgia, Georgia Regents University, Augusta, GA USA.
authors.forename: Jigar
authors.initials: J
authors.lastname: Bhagatwala
authors.affiliation: Georgia Prevention Institute, Medical College of Georgia, Georgia Regents University, Building HS-1640, Augusta, 30912-3715 GA USA.
authors.forename: Haidong
authors.initials: H
authors.lastname: Zhu
authors.affiliation: Georgia Prevention Institute, Medical College of Georgia, Georgia Regents University, Building HS-1640, Augusta, 30912-3715 GA USA ; Department of Internal Medicine, Medical College of Georgia, Georgia Regents University, Augusta, GA USA.
authors.forename: Samip J
authors.initials: SJ
authors.lastname: Parikh
authors.affiliation: Georgia Prevention Institute, Medical College of Georgia, Georgia Regents University, Building HS-1640, Augusta, 30912-3715 GA USA.
authors.forename: De-Huang
authors.initials: DH
authors.lastname: Guo
authors.affiliation: Georgia Prevention Institute, Medical College of Georgia, Georgia Regents University, Building HS-1640, Augusta, 30912-3715 GA USA.
authors.forename: Ishita
authors.initials: I
authors.lastname: Kotak
authors.affiliation: Georgia Prevention Institute, Medical College of Georgia, Georgia Regents University, Building HS-1640, Augusta, 30912-3715 GA USA.
authors.forename: Ying
authors.initials: Y
authors.lastname: Huang
authors.affiliation: Georgia Prevention Institute, Medical College of Georgia, Georgia Regents University, Building HS-1640, Augusta, 30912-3715 GA USA ; College of Nursing, Georgia Regents University, Augusta, GA USA.
authors.forename: Robyn
authors.initials: R
authors.lastname: Havens
authors.affiliation: Georgia Prevention Institute, Medical College of Georgia, Georgia Regents University, Building HS-1640, Augusta, 30912-3715 GA USA.
authors.forename: Michael
authors.initials: M
authors.lastname: Pham
authors.affiliation: Georgia Prevention Institute, Medical College of Georgia, Georgia Regents University, Building HS-1640, Augusta, 30912-3715 GA USA.
authors.forename: Eric
authors.initials: E
authors.lastname: Afari
authors.affiliation: Georgia Prevention Institute, Medical College of Georgia, Georgia Regents University, Building HS-1640, Augusta, 30912-3715 GA USA.
authors.forename: Susan
authors.initials: S
authors.lastname: Kim
authors.affiliation: College of Dental Medicine, Georgia Regents University, Augusta, GA USA.
authors.forename: Christopher
authors.initials: C
authors.lastname: Cutler
authors.affiliation: Georgia Prevention Institute, Medical College of Georgia, Georgia Regents University, Building HS-1640, Augusta, 30912-3715 GA USA.
authors.forename: Norman K
authors.initials: NK
authors.lastname: Pollock
authors.affiliation: Georgia Prevention Institute, Medical College of Georgia, Georgia Regents University, Building HS-1640, Augusta, 30912-3715 GA USA.
authors.forename: Yutong
authors.initials: Y
authors.lastname: Dong
authors.affiliation: Georgia Prevention Institute, Medical College of Georgia, Georgia Regents University, Building HS-1640, Augusta, 30912-3715 GA USA ; Department of Internal Medicine, Medical College of Georgia, Georgia Regents University, Augusta, GA USA.
authors.forename: Anas
authors.initials: A
authors.lastname: Raed
authors.affiliation: Georgia Prevention Institute, Medical College of Georgia, Georgia Regents University, Building HS-1640, Augusta, 30912-3715 GA USA.
authors.forename: Yanbin
authors.initials: Y
authors.lastname: Dong
keywords: 4000 IU vitamin D; African Americans; Dose–response vitamin D; Monthly vitamin D; Overweight/obese