Efficacy of Oral Vitamin B-12 at 1000 Μg Compared With 2000 Μg on Neuropathic Outcomes in Patients With Diabetic Peripheral Neuropathy and Low Serum Vitamin B-12: A Randomized Clinical Trial Publisher Pubmed



Mansour A ; Amrollahi Bioky A ; Gerami H ; Khorasanian AS ; Esmaeili AH ; Fateh HR ; Aghaei Meybodi HR ; Mohajeritehrani MR ; Safyari R ; Adibi H ; Sajjadijazi SM
Source: Journal of Nutrition Published:2026

Abstract

Background: Diabetic peripheral neuropathy (DPN) is the most common complication of type 2 diabetes mellitus (T2DM) and is associated with substantial morbidity, mortality, and healthcare costs. Vitamin B-12 plays a critical role in nerve protection and regeneration. However, clinical evidence regarding the effectiveness and optimal dose of vitamin B-12 supplementation for managing DPN in individuals with low serum vitamin B-12 levels remains inconclusive. Objectives: The aim of this study is to compare the effects of 2 different daily doses of oral vitamin B-12 supplementation on neuropathic parameters in patients with DPN and low serum vitamin B-12. Methods: This 16 wk, randomized controlled trial enrolled adults with T2DM, DPN, and low serum vitamin B12 levels (<200 pg/mL). Patients were randomly assigned (1:1) to receive either 1000 μg or 2000 μg of oral vitamin B12 (methylcobalamin) daily. The primary outcomes were changes in neuropathic parameters, assessed by the numerical rating scale (NRS), Michigan neuropathy screening instrument examination (MNSIE), and neuropathy disability score (NDS). Secondary outcomes included serum B-12 levels and metabolic parameters. Results: Of the 35 participants randomly assigned, 32 completed the 16-wk trial. Serum vitamin B-12 levels increased significantly in both groups, with a greater rise noted in the 2000 μg group (P = 0.049). Both the 1000 μg and 2000 μg groups experienced significant improvements in neuropathy symptoms. Mean ± SD NRS scores decreased from 7.00 ± 2.03 to 5.60 ± 2.19 (P = 0.016) in the 1000 μg group, and from 6.18 ± 2.40 to 4.42 ± 2.50 (P = 0.007) in the 2000 μg group. Similarly, MNSIE scores improved from 5.70 ± 1.66 to 5.22 ± 1.99 (P = 0.033) and from 5.40 ± 1.68 to 4.47 ± 2.25 (P = 0.022), respectively. No significant difference in these neuropathic outcomes was observed between groups. The NDS remained unchanged in both groups (P > 0.05). In addition, the 1000 μg dose was associated with significant improvements in hemoglobin A1c levels, whereas the 2000 μg dose was linked to a significant decline in estimated glomerular filtration rate. Conclusions: In patients with DPN and low serum vitamin B-12 levels, 16 wk of daily supplementation with either 1000 μg or 2000 μg of vitamin B-12 similarly improves neuropathic symptoms. Apart from higher serum B-12 levels, the 2000 μg dose did not offer additional neuropathic or metabolic benefits. © 2026 American Society for Nutrition