title: Factors predicting vitamin D response variation in non-Hispanic white postmenopausal women.
abstract: OBJECTIVE
  It is well documented that there is wide variation in the response of serum 25-hydroxyvitamin D [25(OH)D] to a given dose of vitamin D supplementation. Understanding factors affecting the response variation is important for identifying subjects who are susceptible to vitamin D deficiency or toxicity. This study aimed to evaluate potential predictors for vitamin D response variation.
  
  
  METHODS
  A total of 1179 non-Hispanic white postmenopausal women were enrolled into a 4-yr calcium and vitamin D (1100 IU/d) clinical trial. Among them, serum 25(OH)D level of 1063 subjects were measured at both baseline and after 12 months treatment. Vitamin D response was computed for these 1063 subjects as the difference in levels of serum 25(OH)D concentration at the end of a 12-month vitamin D treatment compared with baseline. Stepwise linear regression was used to identify predictors of vitamin D response variation.
  
  
  RESULTS
  Increase in vitamin D intake, baseline serum 25(OH)D level, baseline blood collection season, baseline serum calcium level, and baseline body mass index were predictors of vitamin D response variation. These five factors explained 46.8% of the vitamin D response variation in the 1063 subjects. The first three factors [increase in vitamin D intake, baseline serum 25(OH)D level, baseline blood collection season] remained as predictors in the 392 subjects with trial vitamin D supplementation. For the first time, our study indicated that season is an important prediction factor for vitamin D response variation. Subjects who started vitamin D treatment in a cold season (autumn and winter) achieved a significantly higher serum 25(OH)D increase than those started in a hot season (summer) (P < 0.001).
  
  
  CONCLUSIONS
  Our study suggests that the increase in vitamin D supplementation, baseline serum 25(OH)D level, and the season when initiating the vitamin D supplementation can partially predict vitamin D response variation in non-Hispanic postmenopausal women.
authors.affiliation: Department of Biostatistics and Bioinformatics, Center for Bioinformatics and Genomics, Tulane University, New Orleans, Louisiana 70112, USA. lzhao2@tulane.edu
authors.forename: Lan-Juan
authors.initials: LJ
authors.lastname: Zhao
authors.forename: Yu
authors.initials: Y
authors.lastname: Zhou
authors.forename: Fengxiao
authors.initials: F
authors.lastname: Bu
authors.forename: Dianne
authors.initials: D
authors.lastname: Travers-Gustafson
authors.forename: An
authors.initials: A
authors.lastname: Ye
authors.forename: Xiaojing
authors.initials: X
authors.lastname: Xu
authors.forename: Lee
authors.initials: L
authors.lastname: Hamm
authors.forename: Daniel Michael
authors.initials: DM
authors.lastname: Gorsage
authors.forename: Xiang
authors.initials: X
authors.lastname: Fang
authors.forename: Hong-Wen
authors.initials: HW
authors.lastname: Deng
authors.forename: Robert R
authors.initials: RR
authors.lastname: Recker
authors.forename: Joan M
authors.initials: JM
authors.lastname: Lappe
mesh_terms: D000368:Aged; D019587:Dietary Supplements; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D008875:Middle Aged; D017698:Postmenopause / Q000378:metabolism*; D012044:Regression Analysis; D012621:Seasons; D014807:Vitamin D / Q000008:administration & dosage* / Q000031:analogs & derivatives* / Q000097:blood
chemical_list: D014807:Vitamin D; C104450:25-hydroxyvitamin D