Tim Spector's book The Diet Myth: The Real Science Behind What We Eat has a chapter on B12 deficiency in vegetarians. He anecdotally found using himself as a tr

Tim Spector's book The Diet Myth: The Real Science Behind What We Eat has a chapter on B12 deficiency in vegetarians. He anecdotally found using himself as a trial that he couldn't retain B12 in blood level tests while on his usual vegetarian diet despite taking large amounts of supplements. He had to get injected B12 to get the same levels in his blood that consuming a rare steak once a month would provide. From a geneticist's viewpoint he ponders if this is some kind of trait left over from evolution. It's a good book if not 'over-written' meaning way too many flowery and very long anecdotes shoved into the research. He has a chapter on 'Vitamin supplement X causes cancer' studies as well.