Adaptive changes in vitamin B12 absorption in celiac disease and after proximal small-bowel resection in man.

Resection of the proximal small bowel is known to cause mucosal hyperplasia and enhanced absorption in the ileum of experimental animals, but similar adaptive changes had not previously been studied in man. Since intrinsic-factor-bound vitamin B12 (IF-B12) absorption is confined to the ileum, as an index of ileal adaptation, we measured whole-body IF-58 Co B12 absorption in 24 control subjects, in 4 patients after proximal small-bowel resection, and in 9 patients with adult celiac disease (where mucosal damage is often limited to the proximal intestine and spares the ileum). Control subjects absorbed 20.4% (+/- 1 SD 6.2%) of the administered 5-mug dose of vitamin B12, while the corresponding 7-day retention values in patients with proximal resection (mean 42.3%; range 32-61%) and in 2 of the 9 celiac patients (44.1% and 54%, respectively), were above the normal range. The increased vitamin B12 absorption in these patients suggest that functional adaptation also occurs in the ileum in man. The results also illustrate the application of a newly developed whole-body counting technique to study vitamin B12 absorption in man.