Vitamin C undergoes enolization to form ascorbic acid. Some mammals have lost the ability to synthesize vitamin C, including simians and tarsiers, which together make up one of two major primate suborders, Haplorrhini. This group includes humans. The other more primitive primates (Strepsirrhini) have the ability to make vitamin C. Synthesis does not occur in most bats nor in species in the rodent family Caviidae, that includes guinea pigs and capybaras, but does occur in other rodents, including rats and mice. Reptiles and older orders of birds make ascorbic acid in their kidneys. Recent orders of birds and most mammals make ascorbic
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