抄録
A brief review has been made of the studies carried out by the author on intestinal absorption of vitamin B_<12>. The absorption of vitamin B_<12> is of a dual mechanism ; intrinsic factor of Castle is involved in the absorption of physiological doses and absorption of supraphysiological doses is effected by concentration gradient not involving intrinsic factor. The former mechanism may consist of at least three steps of a) formation of intrinsic factor-B_<12> complex, b) mucosal adsorption of this complex, and c) transfer of vitamin B_<12> from the complex through the mucosl barrier. No experimental evidence is as yet available to verify that these steps actually occur in the absorption of food vitamin B_<12> in the gut. In addition to these intraluminal factors. vitamin B_<12> absorption is subjected to humoral regulation which acts through the mucosa, as in thyroid disorders and pregnancy. Intestinal flora is another factor to be considered. The significance of this elaborate absorption system is discussed from a nutritional and physiological points of view.
