Vitamin D supplementation increases calcium absorption without a threshold effect

Am J Clin Nutr. 2014 Mar;99(3):624-31. doi: 10.3945/ajcn.113.067199. Epub 2013 Dec 11.


Background: The maximal calcium absorption in response to vitamin D has been proposed as a biomarker for vitamin D sufficiency.

Objective: The objective was to determine whether there is a threshold beyond which increasing doses of vitamin D, or concentrations of serum 25-hydroxyvitamin D [25(OH)D], no longer increase calcium absorption.

Design: This was a placebo-controlled, dose-response, randomized, double-blind study of the effect of vitamin D on calcium absorption in healthy postmenopausal women. Seventy-six healthy postmenopausal women were randomly assigned to placebo or 800 IU (20 μg), 2000 IU (50 μg), or 4000 IU (100 μg) vitamin D₃ for 8 wk. The technique of dual isotopes of stable calcium was used with a calcium carrier to measure calcium absorption at baseline and after 8 wk.

Results: Seventy-one women with a mean ± SD age of 58.8 ± 4.9 y completed the study. The mean calcium intake was 1142 ± 509 mg/d and serum 25(OH)D was 63 ± 14 nmol/L at baseline. A statistically significant linear trend of an increase in calcium absorption adjusted for age and body mass index with increasing vitamin D₃ dose or serum 25(OH)D concentration was observed. A 6.7% absolute increase in calcium absorption was found in the highest vitamin D₃ group (100 μg). No evidence of nonlinearity was observed in the dose-response curve.

Conclusions: No evidence of a threshold of calcium absorption was found with a serum 25(OH)D range from 40 to 130 nmol/L. Calcium absorption in this range is not a useful biomarker to determine nutritional recommendations for vitamin D.

Trial registration: NCT01119378.

Publication types

  • Randomized Controlled Trial

MeSH terms

  • Biomarkers / blood
  • Bone Density Conservation Agents / administration & dosage*
  • Bone Density Conservation Agents / adverse effects
  • Bone Density Conservation Agents / metabolism
  • Bone Density Conservation Agents / therapeutic use
  • Calcifediol / blood
  • Calcium / blood
  • Calcium Isotopes
  • Calcium, Dietary / administration & dosage
  • Calcium, Dietary / metabolism*
  • Cholecalciferol / administration & dosage*
  • Cholecalciferol / adverse effects
  • Cholecalciferol / metabolism
  • Cholecalciferol / therapeutic use
  • Dietary Supplements* / adverse effects
  • Double-Blind Method
  • Female
  • Follow-Up Studies
  • Humans
  • Intestinal Absorption*
  • Middle Aged
  • New York
  • Nutritional Requirements*
  • Osteoporosis, Postmenopausal / blood
  • Osteoporosis, Postmenopausal / metabolism
  • Osteoporosis, Postmenopausal / prevention & control*
  • Postmenopause
  • Seasons
  • Vitamin D Deficiency / blood
  • Vitamin D Deficiency / diet therapy
  • Vitamin D Deficiency / metabolism
  • Vitamin D Deficiency / prevention & control


  • Biomarkers
  • Bone Density Conservation Agents
  • Calcium Isotopes
  • Calcium, Dietary
  • Cholecalciferol
  • Calcifediol
  • Calcium

Associated data