Vitamin B12 Deficiency and Canker Sores — The RCT Evidence

The B12-canker sore connection is one of the better-studied supplement interventions in recurrent aphthous stomatitis (RAS), and the mechanism isn't simply "fix a deficiency."

The Volkov et al. (2009) RCT

The key study: Volkov et al. randomized 58 RAS patients to 1000mcg sublingual B12 nightly versus placebo for 6 months (PMID: 20012098).

Results:

• Number of ulcers: Significantly reduced in the B12 group
• Pain duration: Shorter in the B12 group
• Outbreak-free months: More in the B12 group

The critical finding: benefits occurred regardless of baseline serum B12 levels. Patients with normal B12 levels at the start still showed improvement. This rules out simple deficiency correction as the sole mechanism.

Why B12 Affects Canker Sores Beyond Deficiency

B12 is a cofactor for two enzyme pathways in humans:

1. Methionine synthase — converts homocysteine to methionine, essential for DNA methylation and nucleotide synthesis. Rapidly dividing cells (like oral epithelium, which turns over every 7-14 days) require high rates of DNA synthesis. Impaired methionine synthase slows re-epithelialization.

2. Methylmalonyl-CoA mutase — involved in fatty acid metabolism and myelin synthesis. Less directly relevant to oral mucosa, but B12 deficiency broadly impairs cellular energy metabolism.

The "above-normal benefit" observed in Volkov's RCT suggests B12 may have immune-modulatory effects at higher concentrations — particularly on the T-lymphocyte subset responsible for aphthous tissue destruction. This is biologically plausible but not yet confirmed in mechanistic studies.

Methylcobalamin vs. Cyanocobalamin

The Volkov RCT used sublingual methylcobalamin — the active coenzyme form. Cyanocobalamin (the cheap form in most multivitamins) must be converted to methylcobalamin in the liver; sublingual methylcobalamin bypasses this conversion and achieves higher serum levels.

For RAS specifically, sublingual route matters because:

• Absorption doesn't depend on intrinsic factor (relevant if you have gastric issues)
• Achieves peak levels faster than oral tablet
• The dose (1000mcg) is well above the RDA (2.4mcg) — this is a therapeutic dose, not maintenance

Who Should Try This

Everyone with recurrent canker sores. The evidence supports benefit even without confirmed deficiency. The dose is safe (B12 has no known toxicity at these levels; excess is excreted). The intervention is cheap and low-effort.

Get serum B12 tested anyway — not because the supplement only works if you're deficient, but because values below 200pg/mL indicate deficiency that warrants additional investigation (dietary intake, absorption issues, MTHFR status).

The Limitation

This is one RCT with 58 patients. It hasn't been replicated at scale. The confidence level is "moderate" not "strong" — but for a low-risk, inexpensive intervention with a plausible mechanism, this meets the threshold to recommend for chronic sufferers.