Which of the following increases the absorption of iron?

Question

BlackTom AI · Accepted Answer

Vitamin C (ascorbic acid) increases absorption of dietary iron by chemically reducing ferric iron (Fe3+) to the more soluble ferrous form (Fe2+) and by forming a soluble iron–ascorbate complex that remains absorbable in the small intestine.

1. Relevant knowledge points and concepts
- Two dietary iron forms: heme iron (from animal sources; relatively well absorbed) and nonheme iron (plant sources; absorption is variable and affected by other dietary factors).
- Absorption of nonheme iron depends on its chemical state and solubility in the intestinal lumen.
- Vitamin C is a potent enhancer of nonheme iron absorption. Other common modifiers: meat (enhances), gastric acidity (enhances), and inhibitors like calcium, fiber, phytates and polyphenols (tea, coffee).

2. Step-by-step reasoning
- Dietary nonheme iron is often present as ferric iron (Fe3+), which is less soluble and less readily absorbed.
- Ascorbic acid donates electrons and reduces Fe3+ to Fe2+: Fe3+ + e- → Fe2+.
- Ascorbate also forms a soluble complex with Fe2+ (iron–ascorbate complex), preventing precipitation at intestinal pH and keeping iron available for uptake by enterocytes.
- Therefore, concurrent intake of vitamin C with nonheme iron increases the fraction that crosses the intestinal epithelium into the bloodstream.

3. Chemical intermediate step
- Reduction: Fe3+ + ascorbate → Fe2+ + dehydroascorbate (simplified redox representation).
- Complex formation: Fe2+–ascorbate (soluble complex) → transported into enterocyte via DMT1 transporter.

4. Why the correct answer is correct
- Vitamin C directly alters iron’s oxidation state and solubility, markedly boosting nonheme iron bioavailability; clinical studies show vitamin C co-ingestion increases iron absorption several-fold.

5. Why the other options are incorrect
- Iron (as an answer choice) is ambiguous: consuming more iron can increase intake but does not necessarily increase fractional absorption—absorption is physiologically regulated.
- Calcium inhibits iron absorption when present in meals or supplements.
- Fiber binds iron and speeds transit or forms complexes (phytates/lectins), reducing absorption.

Conclusion: Vitamin C is the factor that increases iron absorption; this matches the provided correct answer, “vitamin c.”

Which of the following increases the absorption of iron?单项选择题

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