Vitamin B12 Status, Metformin Exposure, and Peripheral Neuropathy in Type 2 Diabetes: A Hospital-Based Cross-Sectional Study

Abstract

Background: Long-term metformin use can deplete vitamin B12, but how often this occurs in Indian clinic populations, and whether the resulting deficiency accounts for neuropathy beyond hyperglycaemia, is not settled.

Methods: In a hospital-based cross-sectional study, 60 adults with type 2 diabetes treated with oral glucose-lowering therapy for at least 6 months underwent chemiluminescent immunoassay for fasting serum vitamin B12, glycated haemoglobin, and estimated glomerular filtration rate, together with the Michigan Neuropathy Screening Instrument and bilateral hallux biothesiometry.

Results: Suboptimal vitamin B12 (≤300 pg/mL) was present in half the cohort, including overt deficiency in about one in five. Peripheral neuropathy was found in 55% and increased from normal through borderline to deficient B12 categories. After adjustment, B12 category and glycated haemoglobin were independent correlates of neuropathy. Metformin duration and daily dose, not duration of diabetes, accounted for most of the variation in serum B12. The association between longer metformin use and neuropathy was largely attenuated once serum B12 was included.

Conclusion: Borderline as well as overt B12 depletion marked a higher neuropathy burden. Periodic B12 testing in metformin-treated patients should not wait for advanced disease or for treatment lasting many years.