Br Med J  1971;2:685-687 (19 June), doi:10.1136/bmj.2.5763.685

Vitamin-B₁₂ Status of Patients on Long-term Metformin Therapy

Vitamin-B₁₂ malabsorption has been found in 21 (30%) of 71 diabetic patients taking long-term metformin therapy in addition to dietary management. The patients with evidence of B₁₂ malabsorption had significantly lower haemoglobin levels (and significantly higher serum folic acid levels) than those with normal B₁₂ absorption. Steatorrhoea was found in only one patient. Stopping metformin therapy resulted in reversion of B₁₂ absorption to normal in most patients examined. Four patients with B₁₂ malabsorption were found to have pathologically low serum B₁₂ levels. The causes and implications of these findings are discussed and it is concluded that all patients on long-term metformin therapy should have annual serum B₁₂ estimations.

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