title: Increasing use of vitamin D supplementation in the chronic renal insufficiency cohort study.
abstract: OBJECTIVE
  This study examined rates and determinants of vitamin D supplementation among Chronic Renal Insufficiency Cohort (CRIC) participants and determined the association between dose and 25-hydroxyvitamin D (25(OH)D) level. The 2010 Institute of Medicine Report noted a significant increase in vitamin D supplementation in the general population, but use in chronic kidney disease (CKD) is unknown.
  
  
  METHODS
  CRIC is a multicenter prospective observational cohort study of 3,939 participants with a median baseline age of 60 and an estimated glomerular filtration rate (eGFR) of 42.1 mL/minute per 1.73 m2. Of the cohort, 54.9% was male, 42.1% were Black, and 48.4% were diabetic. Multivariable logistic generalized estimating equations were used to examine determinants of supplementation use assessed annually between 2003 and 2011. Cross-sectional linear regression models, based on a subset of 1,155 participants, assessed associations between supplement dose and 25(OH)D level, measured by high-performance liquid chromatography coupled with tandem mass spectrometry.
  
  
  RESULTS
  The proportion of participants reporting supplement use increased (P < .0001), from 10% at baseline to 44% at 7-year follow-up visits. This was largely due to initiation of products containing only ergocalciferol or cholecalciferol. The odds of supplementation were greater in older, female, non-Black, married participants with greater education and lower body mass index. Among participants taking supplementation, dose was positively associated with 25(OH)D level, adjusted for race, season, diabetes, dietary intake, eGFR, and proteinuria. Only 3.8% of non-Black and 16.5% of Black participants taking a supplement were deficient (<20 ng/mL), whereas 22.7% of non-Black and 62.4% of black participants not reporting supplement use were deficient.
  
  
  CONCLUSIONS
  Vitamin D supplementation rates rose significantly among CRIC participants over 7 years of follow-up and were associated with greater serum 25(OH)D levels. Studies of vitamin D levels on clinical outcomes in CKD and future vitamin D interventional studies should consider these changes in supplementation practices.
authors.affiliation: University of Michigan Medical School and Arbor Research Collaborative for Health, Ann Arbor, Michigan. Electronic address: lmariani@umich.edu.
authors.forename: Laura H
authors.initials: LH
authors.lastname: Mariani
authors.affiliation: The Clinical Research Center, Boston Children's Hospital, Boston, Massachusetts.
authors.forename: Matthew T
authors.initials: MT
authors.lastname: White
authors.affiliation: Department of Biostatistics and Epidemiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania.
authors.forename: Justine
authors.initials: J
authors.lastname: Shults
authors.affiliation: University of California-San Diego School of Medicine, San Diego, California.
authors.forename: Cheryl A M
authors.initials: CA
authors.lastname: Anderson
authors.affiliation: Department of Biostatistics and Epidemiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania; Department of Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania.
authors.forename: Harold I
authors.initials: HI
authors.lastname: Feldman
authors.affiliation: Department of Medicine, Miller School of Medicine, University of Miami, Miami, Florida.
authors.forename: Myles
authors.initials: M
authors.lastname: Wolf
authors.affiliation: Department of Biostatistics and Epidemiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania; Department of Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania.
authors.forename: Peter P
authors.initials: PP
authors.lastname: Reese
authors.affiliation: Department of Pediatrics, Perelman School of Medicine, and the University of Pennsylvania Children's Hospital of Philadelphia, Philadelphia, Pennsylvania.
authors.forename: Michelle R
authors.initials: MR
authors.lastname: Denburg
authors.affiliation: Department of Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania.
authors.forename: Raymond R
authors.initials: RR
authors.lastname: Townsend
authors.affiliation: Kaiser Permanente, Oakland, California.
authors.forename: Joan C
authors.initials: JC
authors.lastname: Lo
authors.affiliation: Department of Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania.
authors.forename: Anne R
authors.initials: AR
authors.lastname: Cappola
authors.affiliation: Department of Pediatrics, Perelman School of Medicine, and the University of Pennsylvania Children's Hospital of Philadelphia, Philadelphia, Pennsylvania.
authors.forename: Dean
authors.initials: D
authors.lastname: Carlow
authors.affiliation: Temple University School of Medicine, Philadelphia, Pennsylvania.
authors.forename: Crystal A
authors.initials: CA
authors.lastname: Gadegbeku
authors.affiliation: St. Johns Health System, Detroit, Michigan.
authors.forename: Susan
authors.initials: S
authors.lastname: Steigerwalt
authors.affiliation: Department of Biostatistics and Epidemiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania; Department of Pediatrics, Perelman School of Medicine, and the University of Pennsylvania Children's Hospital of Philadelphia, Philadelphia, Pennsylvania.
authors.forename: Mary B
authors.initials: MB
authors.lastname: Leonard
mesh_terms: D000367:Age Factors; D000368:Aged; D002762:Cholecalciferol / Q000008:administration & dosage; D015331:Cohort Studies; D003430:Cross-Sectional Studies; D019587:Dietary Supplements; D004872:Ergocalciferols / Q000008:administration & dosage; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D007676:Kidney Failure, Chronic / Q000628:therapy; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D010281:Parathyroid Hormone / Q000097:blood; D011446:Prospective Studies; D051436:Renal Insufficiency, Chronic / Q000188:drug therapy*; D012737:Sex Factors; D014807:Vitamin D / Q000008:administration & dosage* / Q000031:analogs & derivatives / Q000097:blood
chemical_list: D004872:Ergocalciferols; D010281:Parathyroid Hormone; D014807:Vitamin D; D002762:Cholecalciferol; C104450:25-hydroxyvitamin D