Vitamin C as cells rapidly reduce dehydroascorbic acid to ascorbate. SVCTs appear to be the predominant system for vitamin C transport in the body, the notable exception being red blood cells, which lose SVCT proteins during maturation. In both vitamin C synthesizers (example: rat) and non-synthesizers (example: human) cells with few exceptions maintain ascorbic acid concentrations much higher than the approximately 50 micromoles/liter (µmol/L) found in plasma. For example, the ascorbic acid content of pituitary and adrenal glands can exceed 2,000 µmol/L, and muscle is at 200-300 µmol/L. The known coenzymatic functions of ascorbic acid do not require such high concentrations, so
Vitamin B12 leading to vitamin B deficiency. Protein-bound vitamin B must be released from the proteins by the action of digestive proteases in both the stomach and small intestine. Gastric acid releases the vitamin from food particles; therefore antacid and acid-blocking medications (especially proton-pump inhibitors) may inhibit absorption of B. B taken in a low-solubility, non-chewable supplement pill form may bypass the mouth and stomach and not mix with gastric acids, but acids are not necessary for the absorption of free B not bound to protein; acid is necessary only to recover naturally-occurring vitamin B from foods. R-protein (also known as haptocorrin