Vitamin-B12 status of patients on long-term metformin therapy.

Vitamin-B(12) 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 B(12) malabsorption had significantly lower haemoglobin levels (and significantly higher serum folic acid levels) than those with normal B(12) absorption. Steatorrhoea was found in only one patient. Stopping metformin therapy resulted in reversion of B(12) absorption to normal in most patients examined. Four patients with B(12) malabsorption were found to have pathologically low serum B(12) 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 B(12) estimations.