Oral vitamin B₁₂ after total gastrectomy for gastric cancer: mapping the evidence

Abstract Background Patients who undergo total gastrectomy lose the ability to produce intrinsic factor and require lifelong supplementation to prevent vitamin B 12 deficiency. While oral B 12 has emerged as a potential alternative to parenteral therapy, data remain limited, and most clinicians still favor intramuscular injections. This scoping review aimed to map the current evidence on the efficacy, safety, and implementation of oral vitamin B 12 supplementation in patients after total gastrectomy for gastric cancer. Methods We included peer-reviewed studies reporting outcomes of oral vitamin B 12 supplementation after total gastrectomy. A systematic literature search was conducted in scientific databases, including articles published up to November 2025. The reference lists of included articles were screened manually. Extracted data were synthesized narratively. The review was conducted in accordance with the PRISMA-ScR guidelines. Results Seven studies ( n = 449, including 310 patients receiving oral B₁₂) were included. Most used mecobalamin at daily doses of 500–1500 µg. Oral B 12 consistently normalized serum levels and alleviated symptoms in the majority of patients. Comparative studies showed that, in terms of biochemical response, oral supplementation was not inferior to parenteral therapy. However, symptom monitoring was inconsistent, follow-up durations were generally short (< 6 months), and only one study was randomized. Standardized clinical outcome measures were rarely used, and data from Western populations were limited. Heterogeneity in dosing regimens and B 12 formulations further limited comparability across studies. Conclusions Oral B 12 appears to be a feasible route of supplementation after total gastrectomy, but current evidence is limited by heterogeneity, underreporting of clinical outcomes, and lack of long-term follow-up. High-quality trials with standardized outcome measures are warranted.