Malabsorption of food cobalamin.

Food-cobalamin malabsorption is marked by the inability to release cobalamin from food, which therefore cannot be taken up by intrinsic factor for absorption. The defect is not detectable by classical clinical tests like the Schilling test which are all based on the absorption of free, crystalline cobalamin. Tests of food-cobalamin absorption have been devised, the most popular ones using cobalamin bound to eggs or to chicken serum. The disparity between the abnormal results of these tests and the normal results with the Schilling test defines the disorder of food-cobalamin malabsorption. Release of cobalamin from food requires acid and pepsin, and most food-cobalamin malabsorptive states can be traced to gastric defects. However, other mechanisms may also play a role. The malabsorption is limited to food cobalamin and any free cobalamin, presumably including recycled biliary cobalamin, will be absorbed normally, which may explain its frequently insidious nature. The effect on cobalamin status covers a broad spectrum. At one extreme, some individuals, perhaps in the earliest stages, have normal cobalamin status, while at the other extreme may be found deficiency every bit as severe as in the most florid case of pernicious anaemia. Most often, however, the deficiency is mild, frequently marked by only a low serum cobalamin level, mild evidence of metabolic insufficiency and, sometimes, minimal clinical sequelae. Moreover, in some cases the gastric defect progresses and intrinsic factor secretion is affected, thus transforming into classical pernicious anaemia; this is not inevitable, however, and probably occurs in only a minority of patients. The course of food-cobalamin malabsorption is therefore a varied one. Nevertheless, it may be the most common cause of subtle or mild cobalamin deficiency and it is also sometimes associated with severe deficiency. Its identification and treatment need to be considered more widely in the clinical setting.