Iron铁

Two kinds of iron

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两种铁 · 来源截然不同

Dietary iron comes in two forms; chemical state decides its absorption fate.

Heme iron is Fe²⁺ wrapped in a porphyrin ring, sourced from animal hemoglobin and myoglobin (meat, liver, blood, fish). Absorption 15–35%, stable, barely affected by other foods at the same meal. It enters enterocytes directly through HCP1 (heme carrier protein), then HO-1 (heme oxygenase) releases the iron from the porphyrin ring inside the cell.

Non-heme iron is free Fe³⁺/Fe²⁺ from plants (legumes, leafy greens, fortified grains, nuts) plus egg yolk and a few animal sources. Absorption 2–20%, highly variable, dominated by what else is on the plate. It must first be reduced to Fe²⁺, then transported into the enterocyte via DMT1.

Meal-table enhancers and inhibitors:

Enhancers (Fe³⁺ → Fe²⁺ reduction + chelation)	Inhibitors (lock-up / competition)
Vitamin C ~25 mg, doubles absorption	Tea/coffee tannins, ~60% inhibition
Meat/fish at same meal (heme synergy)	Phytate (raw legumes, whole grains)
Citric/lactic acid (fermented foods)	Oxalate (spinach)
Mild acid (lemon water, vinegar)	Calcium/milk (strong non-heme block)

Practical: vegetarians should pair every meal's plant iron with vitamin C, and push tea/coffee an hour after meals.

RDA: men 8, women 18, pregnancy 27 mg/day — women need more than double men, mostly because of menstrual loss.

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Iron铁

Two kinds of iron

Stop 1/7

两种铁 · 来源截然不同

Enhancers (Fe³⁺ → Fe²⁺ reduction + chelation)	Inhibitors (lock-up / competition)
Vitamin C ~25 mg, doubles absorption	Tea/coffee tannins, ~60% inhibition
Meat/fish at same meal (heme synergy)	Phytate (raw legumes, whole grains)
Citric/lactic acid (fermented foods)	Oxalate (spinach)
Mild acid (lemon water, vinegar)	Calcium/milk (strong non-heme block)

Read story