KIN 343 - 8.5 Iron Bioavailability

Iron Bioavailability

  • Iron bioavailability: Ranges from 2% to 33% of dietary iron being absorbed by the body.

    • Low absorption efficiency: Only 2 milligrams out of every 100 milligrams ingested can be absorbed.

    • Iron deficiency is prevalent worldwide, necessitating focus on its absorption.

Enhancers of Iron Absorption

Sugar Compounds

  • Examples: Sorbitol, Fructose

    • Function as chelating agents by weakly binding to iron, keeping it soluble and in a reduced state (ferrous iron), promoting absorption through DMT1.

Organic Acids

  • Examples: Ascorbate (Vitamin C), Citric Acid, Lactic Acid, Tartaric Acid

    • Two main actions:

      1. Chelation of iron maintains its solubility.

      2. Reduction of ferric iron to soluble ferrous iron, enhancing absorption.

    • Vitamin C can work spontaneously to improve the conversion and accessibility of iron or can act as a cofactor for duodenal cytochrome b in iron transport.

Hemoglobin Sources

  • Meat, Poultry & Fish

    • Source of heme iron with dedicated heme carrier protein 1.

    • High protein content stimulates gastric and intestinal secretions, aiding digestion and iron release.

    • Amino acids released during protein digestion can help bind and keep iron in solution, especially if the meal lowers intestinal pH, which favors ferrous iron.

Mucin

  • Major protein in mucus that chelates ferric iron at acidic pH, maintaining iron in a soluble form for better absorption.

Negative Regulators of Iron Absorption

Polyphenols

  • Found in tea and coffee (e.g., EGCG), strong iron chelators.

    • Can reduce iron absorption significantly (up to 60% in conjunction with meals).

    • Form insoluble complexes with iron, rendering it unavailable for absorption.

Oxalate and Phytate

  • Oxalate binds iron to form insoluble complexes.

  • Phytate can bind to divalent cations, inhibiting absorption of iron along with other minerals.

Calcium and Phosphorus

  • High dietary calcium (from supplements or dairy) can decrease iron absorption by 70%.

    • Forms insoluble calcium phosphate complexes with iron, preventing its absorption.

    • High calcium also affects heme iron absorption through effects on ferroportin movement in enterocytes.

High Levels of Other Minerals

  • Zinc, Manganese, Nickel

    • Compete with iron for uptake via the divalent metal transporter 1 (DMT1).

    • Potential negative impact when consumed in excess.

Antacids and Proton Pump Inhibitors

  • Often rich in calcium or aluminum; increase intestinal pH.

    • Higher pH favors formation of insoluble ferric iron that is poorly absorbed.

    • Can decrease the amount of soluble iron available for absorption.