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Editor's Correspondence
April 9, 2007

Metformin and Vitamin B12 Deficiency: Association and Not Causation May Play a Major Role in Cohort Studies

Arch Intern Med. 2007;167(7):730. doi:10.1001/archinte.167.7.730-a

In the October 9th issue of the ARCHIVES, Ting et al1 reported a dose-dependent inverse relationship between daily metformin dosage and low levels of vitamin B12. They also found a higher prevalence of vegetarians in the same group of patients with metformin-related low levels of vitamin B12 (referred to as borderline significant due to a P value of .04 and an odds ratio of 8.19 [95% confidence interval, 0.91-73.9]). The authors tried to suggest a causative relationship and recommend forgoing the annual blood examinations for vitamin B12 levels in metformin-treated patients with diabetes, since the results of such screening should be regarded as obvious.1

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