Calcium Does Not Inhibit the Absorption of 5 Milligrams of Nonheme or Heme Iron at Doses Less Than 800 Milligrams in Nonpregnant Women,

Abstract

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.

Effect of phytic acid, tannic acid and pectin on fasting iron bioavailability both in the presence and absence of calcium

“…In agreement with these results, a previous study performed by us, and recently published by Gaitan et al [15] found that doses ≤800 mg of Ca (CaCl 2 ) did not decrease the bioavailability of 5 mg of Fe (FeSO 4 ) in subjects with similar characteristics. Also, a study focused on the effect of calcium on uptake, efflux, and net absorption of non-heme iron using the intestinal-like epithelial Caco-2 cell found that calcium did not have an effect on the net absorption of non-heme iron [39].…”

“…One study showed an inhibitory effect of phytic acid on iron absorption in the presence of calcium [14]. Although it has been thought that calcium may have a direct inhibitory effect on iron absorption, a recent article [15] showed that doses ≤800 mg of calcium (Ca molar ratio: Fe ≤ 225:1), do not diminish the bioavailability of 5 mg of non-heme iron. Evidence on the interaction between calcium and phytic acid and their effect http://dx.doi.org/10.1016/j.jtemb.2014.…”

Nationwide data on municipal drinking water and hip fracture: Could calcium and magnesium be protective? A NOREPOS study

“…The authors suggested that the reason for the adverse effect may be that physiological changes at the femoral neck are inhibited when high calcium supplementation is taken without vitamin D. An alternative explanation could be a reduced uptake of other potentially bone-essential minerals such as iron with high calcium intake [44,45]. But this inhibitory effect seems to be of short term duration and only present at very high calcium doses [45][46][47].…”

Alginate Inhibits Iron Absorption from Ferrous Gluconate in a Randomized Controlled Trial and Reduces Iron Uptake into Caco-2 Cells

“…In the human study, the calcium dose selected was 600 mg, because this quantity of calcium was required to achieve a calcium:iron molar ratio of 11∶1 with the minimum dose of iron required to produce a measurable serum response (21 mg). A dose-dependent inhibitory effect of calcium on absorption of iron has been reported for molar ratios ranging from 11∶1 (40 mg calcium, 5 mg iron) to 83∶1 (300 mg calcium, 5 mg iron) [25], although more recently a higher threshold molar ratio of 220∶1 (800 mg calcium, 5 mg iron) was reported [26]. Our study demonstrates an inhibitory effect of calcium at a molar ratio of 11∶1 (Figure 3, iron alone 11.5%, iron plus calcium 5.6%, p = 0.014, n = 7).…”