Contributions of heme and nonheme iron to human nutrition

Abstract

Dietary iron is present in food both in inorganic forms as ferrous and ferric compounds, and in organic forms, the most important of these being heme iron. The purpose of this review is to evaluate the contributions of both heme and nonheme iron in establishing and maintaining a healthful iron status. The human requirement for iron, bioavailability of heme and nonheme iron, and amounts of heme and nonheme iron in the diet are individually estimated after reviewing the relevant literature in Sections II, III, and IV, respectively. In Section V, the contribution of heme and nonheme iron to human nutrition, as compared to the human requirement for iron (Section II), is estimated after attenuating the amounts of heme and nonheme iron found in the diet (Section IV) by their bioavailabilities (Section III).

Iron deficiency: A concise review

“…While most iron in the diet is inorganic iron, its absorption ranges from 2% to 20%, so that a large source of iron is from organic sources. In developed countries, perhaps twothirds of the iron is derived from heme [25]. Nonheme iron absorption is facilitated by meat, ascorbic acid, but inhibited by phytates, some dietary fibers and lignins, phenolic polymers, and calcium.…”

Influence of the extent of haemoglobin hydrolysis on the digestive absorption of haem iron in the rat. An in vitro study

“…Peptides and amino acids produced by meat hydrolysis can positively influence the absorption of haem and non-haem iron (Conrad et al 1966;Hallberg et al 1979;Carpenter & Mahoney, 1992); nevertheless, pure haem produced from haemoglobin hydrolysis is poorly absorbed because it forms large, insoluble polymers at low pH (Conrad et al 1966). Optimising the interactions between haem and peptides could improve the absorption of haemoglobin-derived haem iron; providing haem iron in such a complexed form before digestion could contribute to that effect in as much as the most efficient site of iron absorption is the proximal digestive tract (Benito & Miller, 1998).…”

“…Several steps could be critical for the regulation of haem iron absorption (Young et al 1989); both luminal digestion and enterocyte transfer could be involved. The uptake is assumed to be the main determining factor (Roberts et al 1993), particularly at low doses (Hallberg et al 1979); at higher doses the regulation of iron transfer, involving haem splitting in the enterocyte and the rate of transport of iron out of mucosa could be limiting to haem iron absorption in normal animals (Wheby et al 1970;Wheby & Spyker, 1981;Carpenter & Mahoney, 1992). Haem splitting is enhanced in iron-deficient animals (Wheby et al 1970;Raffin et al 1974).…”

Is the calcium transporter a potential candidate for heme transport?

“…Consequently, the enterocyte vectorial apical heme transporter remains elusive and enigmatic in iron metabolism research since HCP1 transports folate with a higher affinity (3,4). There is considerable evidence that the duodenal transporter of heme porphyrin proteins has higher transport kinetics than DMT1, the inorganic iron counterpart (5). It is presumably due, in part, to heme non-reactivity with luminal inhibitory dietary ligands.…”