Clinically significant vitamin B12 deficiency secondary to malabsorption of protein-bound vitamin B12

Abstract

Protein- (chicken serum) bound [57Co]cyanocobalamin absorption was evaluated in five hypochlorhydric patients who had developed B12 deficiency despite having normal absorption of unbound crystalline vitamin B12. All five patients had decreased urinary excretion of protein-bound B12 (0.06--0.34%) as compared to twelve normal controls (0.61--5.6%), P less than .001. Improvement in protein-bound B12 absorption in four of the five patients occurred with the exogenous administration of hydrochloric acid, pepsin, gastric intrinsic factor, or a combination thereof. Vitamin B12 deficiency developing in the setting of hypochlorhydria may result from deficiency of acid-peptic digestion of B12 bound to protein and/or a relative deficiency of intrinsic factor. This digestive defect is not detected with tests which measure the absorption of unbound crystalline B12 but is detected by a simple test which employs B12 bound to chicken serum as the form of protein-bound B12.

Older Men and Women Efficiently Absorb Vitamin B-12 from Milk and Fortified Bread

“…Krasinski et al 1986). Crystalline vitamin B-12 absorption is normal in most people with atrophic gastritis, because intrinsic factor is not lowered to a critical degree (Dawson et al 1984, Doscherholmen et al 1976and 1981, Jones et al 1987, King et al 1979, Suter et al 1993. It is not known how efficient the absorption of vitamin B-12 from milk or fortified bread would be in elderly subjects with atrophic gastritis; however, it has been presumed that vitamin B-12 bioavailability from a fortified cereal product would be as high as that from a dietary supplement in subjects with atrophic gastritis, because crystalline vitamin B-12 is sprayed onto such products.…”

New assay for the rapid determination of plasma holotranscobalamin II levels: Preliminary evaluation in cancer patients

“…In general, a low total plasma B 12 level predicts for a low level of plasma holoTC 11. However, in 34 of 152 cancer patients (22%) included in our study, an abnormal depression in plasma holoTC I1 levels occurred in spite of total plasma B 12 levels in the normal range ( [4][5][6] showing treatment-related lowering of holo-TC I1 levels to the abnormal range in the presence of normal total plasma B 12 levels in patients receiving enterocyte-damaging therapy. Others have demonstrated similar malabsorption of B12 due to irradiation of the small bowel [ 3 8 4 0 ] and in association with the administration of chemotherapy [41,42].…”

Effect of hypochlorhydria due to omeprazole treatment or atrophic gastritis on protein-bound vitamin B12 absorption.

“…The Schilling test using crystalline vitamin B 12 is normal in most cases of atrophie gastritis since intrinsic factor secretion remains adequate. However, in atrophie gastritis the absorption of protein-bound vita min Bi2 is diminished [13,14,[17][18][19]. Protein-bound vita min Bu malabsorption has also been shown to occur in hypochlorhydric states due to H 2 -blocker therapy and post gastrectomy or vagotomy [20][21][22].…”