title: Can vitamin D metabolite measurements facilitate a "treat-to-target" paradigm to guide vitamin D supplementation?
abstract: Substantial variability exists in the serum 25(OH)D increase observed in response to vitamin D supplementation. Measurement of circulating cholecalciferol and 24,25(OH)₂D, as indicators of vitamin D absorption and degradation, respectively, account for approximately half of the variation in serum 25(OH)D observed following supplementation.
  
  
  BACKGROUND
  Vitamin D supplementation produces a variable response in serum 25(OH)D. This variability likely reflects, in part, differences in vitamin D absorption and/or degradation. Despite this variation in response, virtually all expert recommendations endorse a fixed vitamin D supplementation dose, an approach also used in most prospective studies. Such utilization of a single vitamin D dose does not assure attaining any pre-specified target 25(OH)D level, thereby compromising clinical care and prospective supplementation trials. This study begins addressing this weakness by exploring the feasibility of vitamin D metabolite measurements to predict serum 25(OH)D level attained following supplementation.
  
  
  METHODS
  Ninety-one community-dwelling postmenopausal women with baseline 25(OH)D of 10-30 ng/mL received oral vitamin D₃, 2300 or 2500 IU, daily for 4-6 months. Serum 25(OH)D, cholecalciferol (D₃), and 24,25(OH)₂D were measured before and at the end of supplementation to determine if metabolite concentrations allow prediction of the 25(OH)D level attained.
  
  
  RESULTS
  From baseline and follow-up data, we derived a multiple linear regression model predicting posttreatment 25(OH)D as follows: final 25(OH)D = 8.3 + (1.05*initial 25(OH)D) - (7.7*initial 24,25(OH)₂D) + (0.53*final D₃) + (4.2*final 24,25(OH)₂D). This model has an adjusted R(2) = 0.55, thus accounting for approximately half of the observed variance in the final 25(OH)D level.
  
  
  CONCLUSIONS
  The contributions of circulating cholecalciferol and 24,25(OH)₂D to this predictive model can be considered as indicators of intestinal absorption and clearance, respectively. This paradigm requires further study; it may allow efficient "treat-to-25(OH)D-target" strategies useful in optimizing prospective studies and clinical practice.
authors.affiliation: Osteoporosis Clinical Research Program, University of Wisconsin, 2870 University Avenue, Suite 100, Madison, WI, 53705, USA, nbinkley@wisc.edu.
authors.forename: N
authors.initials: N
authors.lastname: Binkley
authors.forename: J
authors.initials: J
authors.lastname: Lappe
authors.forename: R J
authors.initials: RJ
authors.lastname: Singh
authors.forename: S
authors.initials: S
authors.lastname: Khosla
authors.forename: D
authors.initials: D
authors.lastname: Krueger
authors.forename: M K
authors.initials: MK
authors.lastname: Drezner
authors.forename: R D
authors.initials: RD
authors.lastname: Blank
mesh_terms: D015650:24,25-Dihydroxyvitamin D 3 / Q000097:blood; D000368:Aged; D050071:Bone Density Conservation Agents / Q000627:therapeutic use*; D002762:Cholecalciferol / Q000627:therapeutic use*; D019587:Dietary Supplements; D016903:Drug Monitoring / Q000379:methods; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008875:Middle Aged; D015663:Osteoporosis, Postmenopausal / Q000097:blood / Q000188:drug therapy*; D014807:Vitamin D / Q000031:analogs & derivatives / Q000097:blood
chemical_list: D050071:Bone Density Conservation Agents; D014807:Vitamin D; D002762:Cholecalciferol; D015650:24,25-Dihydroxyvitamin D 3; C104450:25-hydroxyvitamin D