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Diabetes Care. 2000 Sep;23(9):1227-31.

Increased intake of calcium reverses vitamin B12 malabsorption induced by metformin.

Author information

  • 1Department of Medicine, Mount Sinai School of Medicine, New York, USA. bauman.william@bronx.va.gov

Abstract

OBJECTIVE:

Of patients who are prescribed metformin, 10-30% have evidence of reduced vitamin B12 absorption. B12-intrinsic factor complex uptake by ileal cell surface receptors is known to be a process dependent on calcium availability Metformin affects calcium-dependent membrane action. The objective of this study was to determine the magnitude and mechanism of the reduction in serum vitamin B12 after metformin administration.

RESEARCH DESIGN AND METHODS:

A comparative study design was employed using 2 groups (metformin and control). A total of 21 patients with type 2 diabetes received sulfonylurea therapy; 14 of these 21 patients were switched to metformin. Monthly serum total vitamin B12 measurements and holotranscobalamin (holoTCII) (B12-TCII) were performed. After 3 months of metformin therapy, oral calcium supplementation was administered.

RESULTS:

Serial serum vitamin B12 determinations revealed a similar decline in vitamin B12 and holoTCII. Oral calcium supplementation reversed the metformin-induced serum holoTCII depression.

CONCLUSIONS:

Patients receiving metformin have diminished B12 absorption and low serum total vitamin B12 and TCII-B12 levels because of a calcium-dependent ileal membrane antagonism, an effect reversed with supplemental calcium.

PMID:
10977010
[PubMed - indexed for MEDLINE]
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