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Long-Term and High-Dose Metformin Use Can Compromise B12 Levels

Wednesday, July 25, 2007 by: Jack Challem
Tags: metformin, vitamin B12, health news

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Metformin, a glucose-lowering drug, is one of the most widely prescribed drugs for type-2 (adult-onset) diabetes. But the longer a person takes the drug, especially at high dosages, the more likely he will develop a deficiency of vitamin B12.

Researchers have known since the early 1970s that almost one-third of patients taking metformin have problems absorbing vitamin B12. Studies have found that metformin reduces blood levels of the vitamin by 14 to 30 percent.

In the most recent study along these lines, Kai Ming Chow, MRCP, a physican at the Prince of Wales Hospital, Hong Kong, investigated 155 diabetic patients who developed vitamin B12 deficiency after taking metformin. Chow also studied 310 diabetic patients taking metformin but with no signs of vitamin B12 deficiency.

Patients taking metformin for three or more years were almost two and one-half times more likely to develop vitamin B12 deficiency. Furthermore, each 1-gram increase in the daily dosage almost tripled the risk of vitamin B12 deficiency.

Vegetarians, who are at particular risk of vitamin B12 deficiency, were about eight times more likely to have a deficiency when taking metformin.

Some evidence indicates that metformin may interfere with absorption of vitamin B12 in the ileum, the last part of the small intestine.


Teng RZW, Szeto CC, Chan MHM, et al. Risk factors of vitamin B12 deficiency in patients receiving metformin. Archives of Internal Medicine, 2006;166:1975-1979.

About the author

Jack Challem, known as The Nutrition Reporter(tm), is a personal nutrition coach based in Tucson, Arizona. Jack is one of America's most trusted nutrition and health writers, and has written about research on nutrition, vitamins, minerals, and herbs for more than 30 years. He is the author of The Food-Mood Solution: The Nutrition and Lifestyle Plan to Feel Good Again (Wiley, 2007), Feed Your Genes Right (Wiley, 2005), The Inflammation Syndrome (Wiley, 2003) and the lead author of the best-selling Syndrome X: The Complete Nutritional Program to Prevent and Reverse Insulin Resistance (Wiley, 2000). His next book, Stop Prediabetes Now, will be published in the fall of 2007. He writes The Nutrition Reporter(tm) newsletter and contributes regularly to many magazines, including Alternative Medicine, Better Nutrition, Body & Soul, Experience Life, and Let's Live. Jack's scientific articles have appeared in Free Radical Biology & Medicine, Journal of Orthomolecular Medicine, Medical Hypotheses, and other journals. In addition, he is a columnist for Alternative & Complementary Therapies. Jack is a frequent speaker at nutritional medicine conferences and to consumer health groups. Email him via www.foodmoodsolution.com

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