B12 for Diabetic Nerve Pain: Does It Help?

observational-study PMID: 33513879

Quick Summary: A recent study found that taking vitamin B12 supplements for a year helped reduce nerve pain and improve quality of life in people with diabetes who also had low B12 levels.

What The Research Found

The study looked at people with type 2 diabetes who had nerve damage (diabetic neuropathy) and low levels of vitamin B12. Those who took a daily B12 supplement saw:

Less nerve pain: They reported lower pain scores.

Better nerve function: Tests showed improved nerve signals.

Improved quality of life: They felt better overall.

Study Details

Who was studied: 90 adults with type 2 diabetes, nerve damage, and low B12 levels. They were all taking metformin, a common diabetes medication.

How long: The study lasted for 1 year (12 months).

What they took: Half the group took a daily B12 supplement (1000 mcg of methylcobalamin), and the other half took a placebo (a "dummy" pill).

What This Means For You

If you have diabetes, take metformin, and experience nerve pain (like tingling, numbness, or burning in your feet or hands), talk to your doctor about getting your B12 levels checked. If you're low in B12, this research suggests that taking a B12 supplement could help reduce your pain and improve your quality of life. Important: This study only looked at people with low B12 levels. Taking B12 if you already have enough might not help.

Study Limitations

Specific Group: The study only included people with diabetes who were taking metformin and had low B12. The results might not apply to everyone with diabetic neuropathy.

Autonomic Nerve Issues: The B12 supplement did not improve problems with the autonomic nerves (nerves that control things like heart rate and blood pressure).

More Research Needed: While promising, more research is needed to confirm these findings and understand the long-term effects.

Key Findings

Oral methylcobalamin (1000 μg/day) for 12 months significantly increased serum B12 levels (from 232.0 ± 71.8 to 776.7 ± 242.3 pmol/L) in deficient type 2 diabetes patients on metformin. Treatment improved neurophysiological parameters (sural nerve conduction velocity, sural nerve action potential amplitude, vibration perception threshold), sudomotor function (electrochemical skin conductance in hands/feet), pain scores, and quality of life. No improvement occurred in cardiovascular autonomic reflex tests (CARTs: mean circular resultant, Valsalva test, postural index, orthostatic hypotension) or Michigan Neuropathy Screening Instrument Examination (MNSIE) scores.

Study Design

Randomized, double-blind, placebo-controlled trial (interventional, not observational as mislabeled). 90 adults with type 2 diabetes on metformin ≥4 years, confirmed peripheral/autonomic diabetic neuropathy, and baseline B12 <400 pmol/L. Randomized to active (n=44) or placebo (n=46) for 12 months. Primary outcomes: neurophysiological, autonomic, and quality-of-life metrics.

Dosage & Administration

1000 μg/day oral methylcobalamin (active group) or identical placebo, administered daily for 12 months. All participants had baseline B12 deficiency (<400 pmol/L).

Results & Efficacy

B12 levels rose significantly in the treatment group (p<0.001, implied by magnitude of change). Neurophysiological improvements included:
- Increased sural nerve conduction velocity (SNCV)
- Higher sural nerve action potential amplitude (SNAP)
- Reduced vibration perception threshold (VPT)
Sudomotor function (ESCH/ESCF via SUDOSCAN), pain scores, and quality-of-life metrics showed statistically significant improvement (p-values not provided in source summary). No significant changes occurred in CARTs or MNSIE (p>0.05 for these endpoints).

Limitations

Small sample size (n=90); exclusively enrolled metformin users with pre-existing B12 deficiency, limiting generalizability to non-deficient or non-metformin-treated diabetics. No quantitative effect sizes or exact p-values reported for secondary outcomes in the provided summary. Duration (1 year) may be insufficient to assess long-term neuropathy progression. Autonomic function (CARTs) showed no benefit, indicating selective efficacy.

Clinical Relevance

This supports high-dose oral methylcobalamin (1000 μg/day) as a targeted therapy for B12-deficient type 2 diabetes patients on long-term metformin to alleviate neuropathic pain, improve nerve conduction, and enhance quality of life. It does not support B12 supplementation for autonomic neuropathy symptoms or for non-deficient individuals. Clinicians should screen metformin users for B12 deficiency and consider supplementation at this dose specifically for peripheral neuropathy symptom management in deficient patients. General B12 supplementation for diabetic neuropathy without confirmed deficiency is not indicated by this study.