--but Rose and Mrs. D have reported about nitrous oxide depleting B12 in susceptible people and leading to neurological symptoms:

http://psychology.wikia.com/wiki/Nitrous_oxide

http://www.umm.edu/altmed/drugs/nitr...ide-091811.htm

http://www.ncbi.nlm.nih.gov/pubmed/8250714

http://www.ncbi.nlm.nih.gov/pubmed/8...ubmed_RVDocSum

http://jama.ama-assn.org/cgi/content...ct/255/12/1605

http://journals.lww.com/anesthesiolo...&type=fulltext

There's considerably more available through PubMed and Google Scholar, but you get the idea--it's definitely an area of concern.