can be towards organic substances not metal, havnt u taken ur mother's breast milk, it to contains b12, i hope u r not just a fresh new-born to whom nothing is given. take pasturized milk with out boiling it, take non-veg, eggs. take b12/folic acid
injections if severe enough. go for medicines mostly u wont have any problems, or atleast that problem will be less severe than 12-deficiency. consult a doctor.