What is new in vitamin B(12)?

Neurologic aspects of cobalamin (B12) deficiency

Optimal functioning of the central and peripheral nervous system is dependent on a constant supply of appropriate nutrients. Particularly important for optimal functioning of the nervous system is cobalamin (vitamin B12). Cobalamin deficiency is particularly common in the elderly and after gastric surgery. Many patients with clinically expressed cobalamin deficiency have intrinsic factor-related malabsorption such as that seen in pernicious anemia. The commonly recognized neurological manifestations of cobalamin deficiency include a myelopathy with or without an associated neuropathy. This review deals with neurological aspects of vitamin B12 deficiency and attempts to highlight recent developments.

Role of intestinal transporters in neonatal nutrition: carbohydrates, proteins, lipids, minerals, and vitamins

To support rapid growth and a high metabolic rate, infants require enormous amounts of nutrients. The small intestine must have the complete array of transporters that absorb the nutrients released from digested food. Failure of intestinal transporters to function properly often presents symptoms as "failure to thrive" because nutrients are not absorbed and as diarrhea because unabsorbed nutrients upset luminal osmolality or become substrates of intestinal bacteria. We enumerate the nutrients that constitute human milk and various infant milk formulas, explain their importance in neonatal nutrition, then describe for each nutrient the transporter(s) that absorbs it from the intestinal lumen into the enterocyte cytosol and from the cytosol to the portal blood. More than 100 membrane and cytosolic transporters are now thought to facilitate absorption of minerals and vitamins as well as products of digestion of the macronutrients carbohydrates, proteins, and lipids. We highlight research areas that should yield information needed to better understand the important role of these transporters during normal development.

Vitamin B12 deficiency in hypersecretors during long-term acid suppression with proton pump inhibitors

BACKGROUND

Proton pump inhibitors (PPIs) may cause cyanocobalamin (vitamin B12) malabsorption, but measuring serum B12 alone may underestimate the prevalence. However, B12 deficiency elevates methylmalonic acid and homocysteine, both additional markers of B12 deficiency.

AIM

To determine the true prevalence of B12 deficiency and whether acid suppression by PPI caused it.

METHODS

Sixty-one acid hypersecretors (basal acid output >15 mmol/h), 46 with gastrinoma [Zollinger-Ellison (ZE) syndrome] and 15 without [acid hypersecretor without gastrinoma (pseudo-ZE)], were treated with lansoprazole to determine its long-term (up to 18 years) pharmacological and clinical efficacy and safety, particularly as regards malabsorption of B12.

RESULTS

Of 61 patients, six (10%) had low serum B12. Additional tests uncovered B12 deficiency in 13 (31%) of 41 still-available patients, despite normal serum B12. B12 replacement reduced elevated homocysteine and methylmalonic acid, supporting the diagnosis. Also, measuring both basal and stimulated gastric secretion, we found that acid suppression was neither prolonged nor profound enough to explain the B12 deficiency.

CONCLUSIONS

In long-term recipients of PPIs, B12 deficiency was more frequent (29%) than detected by measuring only serum B12, and there was not enough acid suppression to explain this deficiency.

Vitamin B12 malabsorption in patients with limited ileal resection

OBJECTIVES

Patients with Crohn's disease who have terminal ileal resections are at risk for vitamin B12 malabsorption. Our aim was to determine whether the length of terminal ileum resected correlated with an abnormal Schilling test result.

METHODS

Patients with a history of ileal resection had the length of small bowel removed determined by review of their pathology report. Patients who had a Schilling test within 3 mo of surgery or who had a documented normal terminal ileum at the time of the Schilling test were included in the study.

RESULTS

Fifty-six patients were included in the study. Patients who had <20 cm of terminal ileum resected (n = 14) did not develop abnormal Schilling test results; 52% of the remainder (n = 42) had abnormal Schilling test results and there was no clear correlation between resection length and abnormal Schilling test result.

CONCLUSIONS

Patients with Crohn's disease and terminal ileal resections <20 cm are not at risk of developing vitamin B12 deficiency. For patients with resections of 20-60 cm, options include doing a Schilling test and treating those with abnormal results, empirically treating patients on the presumption that they are at high risk of developing deficiency, or monitoring for biochemical evidence of deficiency. Further studies are needed to determine whether oral supplementation is effective in these patients.

Intestinal absorption of water-soluble vitamins: an update

PURPOSE OF REVIEW

The molecular biology revolution has led to a significant improvement in our understanding of biological and physiological processes. Such expansion of knowledge has also covered the field of intestinal absorption of water-soluble vitamins and is the subject of this review.

RECENT FINDINGS

Impressive progress has been made in the understanding of the mechanisms and regulation of transport of water-soluble vitamins at the cellular and molecular levels. In addition, the 5' regulatory regions of the genes that encode a number of the involved transporters have been cloned and characterized in vitro and in vivo in transgenic mice, thus providing important information about transcriptional regulation of these events. Furthermore, confocal imaging of live intestinal epithelial cells has led to significant progress in understanding the mechanisms involved in intracellular trafficking and membrane targeting of the carrier proteins and how clinical mutations lead to interference with transport. Finally, the identification in the large intestine of efficient and specialized carrier-mediated systems that are capable of absorbing a number of the bacterially synthesized vitamins (thiamin, folate, biotin, riboflavin, pantothenic acid) has raised the possibility that this source of vitamins may play a role in regulating (fine tuning) the normal body homeostasis of these vitamins, and especially the vitamin level in the local colonocytes.

SUMMARY

Water-soluble vitamin absorption involves regulated and specific mechanisms. Interference with the function of these mechanisms may lead to deficiency. The large intestine is capable of absorbing water-soluble vitamins that are synthesized by the normal microflora.