title: The effect of vitamin D on calcium absorption in older women.
abstract: BACKGROUND
  Vitamin D is often recommended for use with calcium supplements to increase absorption. There are no systematic studies of vitamin D on calcium absorption that indicate what dose should be recommended.
  
  
  OBJECTIVE
  Our objective was to study the effect of increasing doses of vitamin D3 on calcium absorption.
  
  
  METHODS
  We conducted a randomized double-blind placebo-controlled trial at Creighton University Medical Center, Omaha, NE.
  
  
  METHODS
  Participants included 163 postmenopausal Caucasian women with vitamin D insufficiency, defined as a serum 25-hydroxyvitamin D (25OHD) below 20 ng/ml (50 nmol/liter).
  
  
  METHODS
  Participants were randomized to receive one of the vitamin D3 doses, 400, 800, 1600, 2400, 3200, 4000, or 4800 IU/d, or placebo for 1 yr. Calcium intake was increased to 1200-1400 mg daily by giving daily calcium citrate.
  
  
  RESULTS
  We evaluated the change in calcium absorption on vitamin D.
  
  
  RESULTS
  Mean serum 25OHD increased from baseline 15.6 ng/ml (39 nmol/liter) to 46.5 ng/ml (112 nmol/liter) in subjects randomized to the highest dose of vitamin D (4800 IU). Calcium absorption was more significantly related to serum 25OHD (R2=0.50; P=0.001) than dose (R2=0.47; P=0.033). Calcium absorption of a 100-mg dose increased from 52-58% (6 mg) over a serum 25OHD range of 20-66 ng/ml (50-165 nmol/liter).
  
  
  CONCLUSIONS
  There was no evidence of a threshold for reduced calcium absorption in the serum 25OHD range of 10-66 ng/ml (25-165 nmol/liter). The increase in absorbed calcium of 6% on high doses of vitamin D is so small that the same amount could be obtained from half a glass of milk (100 ml) or 100 mg elemental calcium. The results challenge assumptions about the value of adding vitamin D to increase calcium absorption except when serum 25OHD is very low that is less than 10 ng/ml (25 nmol/liter).
authors.affiliation: Bone Metabolism Unit, Creighton University Medical Center, 601 North 30th Street, Suite 6718, Omaha, Nebraska 68131, USA. jcg@creighton.edu
authors.forename: J Christopher
authors.initials: JC
authors.lastname: Gallagher
authors.forename: Vinod
authors.initials: V
authors.lastname: Yalamanchili
authors.forename: Lynette M
authors.initials: LM
authors.lastname: Smith
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019355:Calcium Citrate / Q000493:pharmacokinetics*; D002762:Cholecalciferol / Q000008:administration & dosage*; D004305:Dose-Response Relationship, Drug; D004311:Double-Blind Method; D004347:Drug Interactions; D005260:Female; D005500:Follow-Up Studies; D005503:Food Additives / Q000493:pharmacokinetics; D006801:Humans; D007408:Intestinal Absorption / Q000187:drug effects*; D008875:Middle Aged; D017698:Postmenopause / Q000378:metabolism; D016896:Treatment Outcome; D014807:Vitamin D / Q000031:analogs & derivatives / Q000097:blood; D014808:Vitamin D Deficiency / Q000188:drug therapy* / Q000378:metabolism; D014815:Vitamins / Q000008:administration & dosage*
chemical_list: D005503:Food Additives; D014815:Vitamins; D014807:Vitamin D; D002762:Cholecalciferol; C104450:25-hydroxyvitamin D; D019355:Calcium Citrate