Vitamin B12 deficiency<\/a> include decreased absorption in ileum which can be seen in\npatients with Crohn\u00e2\u20ac\u2122s disease, resection of ileum and tapeworm infection. Also,\nin patients having decreased intrinsic factor, there is risk of Vitamin B12\ndeficiency which can be due to atrophic gastritis, pernicious anemia and\npostgastrectomy syndrome. Genetic factors such as deficiency of transcobalamin\ncan also be another risk factor. Persons who are older than 50 years, follow a\nvegetarian diet or are heavy drinkers fall in the category of risk of Vitamin\nB12 deficiency. Those who have been taking medications for a long time such as\nusing Histamine H2 blocker for 12 months, Metformin for more than four months\nand Proton pump inhibitor for more than 12 months also are under the risk\nfactor for Vitamin B12 deficiency. Factors such as smoking, drinking heavy\nalcohol or chronic (from a long time) alcoholism, pregnancy can also cause a\ndeficiency of Vitamin B12.<\/p>\n\n\n\n