Using extraction procedures in which the extracted vitamin B12 was protected by cyanide or metabisulfite, several investigators found no change in vitamin B12 when meals were incubated in the presence of ascorbic acid for 30 minutes at 37 °C. A previous report suggested degradation of vitamin B12 under these conditions, but this was apparently caused by incomplete protection of the extracted vitamin B12 in the assay procedure. If incubation at 37 °C for 30 minutes is a laboratory mimic of the gastric environment, one must conclude that high doses of ascorbic acid do not affect the stability of vitamin B12 in vivo.
(JAMA 242:2319-2320, 1979)
Newmark HL, Scheiner JM, Marcus M, Prabhudesai M. Ascorbic Acid and Vitamin B12. JAMA. 1979;242(21):2319–2320. doi:10.1001/jama.1979.03300210045022