Iron, B12, and folate metabolism
The three haematinics
- The three haematinics. Each has a different absorption site, a different store size, and a different failure mode
| Absorbed | Store | Store lasts | Deficiency picture | |
|---|---|---|---|---|
| Iron | Duodenum + proximal jejunum | 3-4 g (~2/3 in Hb) | ~1-3 yr | Microcytic, hypochromic |
| B12 | Terminal ileum (needs IF) | 2-5 mg, liver | 2-4 years | Macrocytic + neurological |
| Folate | Jejunum (PCFT) | 10-20 mg | ~3-4 months | Macrocytic, no neurology |
- *Store size explains the tempo: folate deficiency appears within months of poor intake, B12 deficiency takes years - so new B12 deficiency is nearly always malabsorption, not diet* (except strict vegans)
- Iron has no regulated excretory route - balance is controlled entirely at absorption -> overload if absorption is unregulated
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