Vitamin B-12 deficiency after gastric surgery for obesity.

Low serum vitamin B-12 concentrations after gastric bypass (GB) surgery for obesity were observed in 11 of 28 patients without detectable impairment of crystalline vitamin B-12 absorption. This was observed in 2 of 19 patients with vertical banded gastroplasty (VBG). In contrast, protein-bound vitamin B-12 absorption was markedly impaired, as demonstrated in eight of these patients after GB (n = 7) and VBG (n = 1). Correction of this impaired absorption occurred when protein-bound vitamin B-12 was incubated with an enzyme mixture before consumption. Simultaneous ingestion of the enzyme mixture with protein-bound vitamin B-12 did not improve absorption of the vitamin. In a separate experiment, 10 patients with a normal result from the Schilling test failed to correct low serum vitamin B-12 concentrations with a quantity of oral crystalline vitamin B-12 equal to the recommended dietary allowance of 2 micrograms, taken twice daily for 3 mo. Serum total homocysteine values declined during this interval. An oral daily dose of 350 micrograms crystalline vitamin B-12 raised the average serum vitamin B-12 concentration to an amount greater than the lower reference limit. A dose > 350 micrograms/d was required to raise all patients' vitamin B-12 concentrations above this concentration rather than just above the population mean. We conclude that because concentrations of oral crystalline vitamin B-12 were required to normalize serum vitamin B-12 concentrations, that a mechanism other than formation of a vitamin B-12 intrinsic factor complex is responsible for crystalline vitamin B-12 absorption after GB for obesity.