Calcium does not inhibit the absorption of 5 milligrams of nonheme or heme iron at doses less than 800 milligrams in nonpregnant women

J Nutr. 2011 Sep;141(9):1652-6. doi: 10.3945/jn.111.138651. Epub 2011 Jul 27.


Calcium is the only known component in the diet that may affect absorption of both nonheme and heme iron. However, the evidence for a calcium effect on iron absorption mainly comes from studies that did not isolate the effect of calcium from that of other dietary components, because it was detected in single-meal studies. Our objective was to establish potential effects of calcium on absorption of nonheme and heme iron and the dose response for this effect in the absence of a meal. Fifty-four healthy, nonpregnant women were selected to participate in 4 iron absorption studies using iron radioactive tracers. We evaluated the effects of calcium doses between 200 and 1500 mg on absorption of 5 mg nonheme iron (as ferrous sulfate). We also evaluated the effects of calcium doses between 200 and 800 mg on absorption of 5 mg heme iron [as concentrated RBC (CRBC)]. Calcium was administered as calcium chloride in all studies and minerals were ingested on an empty stomach. Calcium doses ≥1000 mg diminished nonheme iron absorption by an average of 49.6%. A calcium dose of 800 mg diminished absorption of 5 mg heme iron by 37.7%. In conclusion, we demonstrated an isolated effect of calcium (as chloride) on absorption of 5 mg of iron provided as nonheme (as sulfate) and heme (as CRBC) iron. This effect was observed at doses higher than previously reported from single-meal studies, starting at ~800 mg of calcium.

Publication types

  • Controlled Clinical Trial

MeSH terms

  • Adult
  • Anemia, Iron-Deficiency / drug therapy
  • Calcium / administration & dosage
  • Calcium / pharmacology*
  • Dietary Supplements
  • Dose-Response Relationship, Drug
  • Drug Interactions
  • Female
  • Heme / pharmacokinetics*
  • Humans
  • Iron / administration & dosage*
  • Iron / pharmacokinetics*
  • Iron / therapeutic use
  • Middle Aged


  • Heme
  • Iron
  • Calcium