Nutritional vitamin-B12 deficiency. Possible contributory role of subtle vitamin-B12 malabsorption

Dietary deficiency of vitamin B-12 has been reported, yet most people ingesting vitamin-B12-deficient diets even for many years appear to achieve a balance that does not lead to overt signs and symptoms of deficiency. I present the case of a vegan of 25 years' duration who developed severe neurologic abnormalities due to vitamin-B12 deficiency. His diet provided 1.2 microgram of vitamin B12 daily at most. Despite normal Schilling test findings, he absorbed subnormal amounts of vitamin B12 given with ovalbumin. This poor absorption appeared to be related to his gastritis, achlorhydria, and subnormal intrinsic-factor secretion. Probably, vitamin-B12 deficiency in this patient resulted from both dietary restriction and the subtle malabsorption, neither of which would have sufficed alone to produce the clinical problem. Possibly such malabsorption may also be present in many of those vegans developing overt vitamin-B12 deficiency in whom Schilling test findings have been normal.