Gastrointestinal absorption ascorbate

The gastrointestinal absorption of ascorbate should be considered before summarizing this study. In no case did we achieve a complete recovery of the administered radioactively labeled ascorbic acid. In a separate set of experiments (7), the subjects were equilibrated on a limited intake of ascorbate and given a small oral dose of labeled ascorbate together with about 30 mg of carrier ascorbate (7). After a few hours this intake was followed by large intakes of unlabeled... 

Gastrointestinal absorption increased when plutonium was administered on an empty stomach. In hamsters that had been fasted for 8 to 24 hours, absorption increased to 0.1 to 0.15% of the administered plutonium citrate or ascorbate compared to 0.01 % in animals which had not been fasted (Harrison et al. 1986). 

In the enterocyte as it enters the absorptive zone near to the villus tips, dietary iron is absorbed either directly as Fe(II) after reduction in the gastrointestinal tract by reductants like ascorbate, or after reduction of Fe(III) by the apical membrane ferrireductase Dcytb, via the divalent transporter Nramp2 (DCT1). Alternatively, haem is taken up at the apical surface, perhaps via a receptor, and is degraded by haem oxygenase to release Fe(II) into the same intracellular pool. The setting of IRPs (which are assumed to act as iron biosensors) determines the amount of iron that is retained within the enterocyte as ferritin, and that which is transferred to the circulation. This latter process is presumed to involve IREG 1 (ferroportin) and the GPI-linked hephaestin at the basolateral membrane with incorporation of iron into apotransferrin. (b) A representation of iron absorption in HFE-related haemochromatosis. 

Absorption of iron by the individual varies with age, iron status, the amount and chemical form of the iron ingested, and with conditions in the gastrointestinal tract, only about 5—15% of iron in the diet being normally absorbed. Ferrous iron, as the sulphate, gluconate, fumarate or lactate or as ferrous ammonium sulphate, is appreciably taken up into the bloodstream from the duodenum, especially in the presence of ascorbic acid, a reducing agent. Little difference was found in the extent of their absorption between ferrous sulphate and the various chelates, but ferric ammonium citrate or polysaccharide complexes were only very poorly absorbed22)... 

Vitamin C [ascorbic acid) Men 90 mg/d Women 75 mg/d Cofactor for reactions requiring reduced copper or iron met-alloenzyme and as a protective antioxidant prevents scurvy Gastrointestinal disturbances, kidney stones, excess iron absorption... 

Domingo JL, Gomez M, Llobet JM, Richart C. Effect of ascorbic acid on gastrointestinal aluminium absorption. Lancet I99I 338(8780) I467. 

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