RT Journal Article SR Electronic T1 Vitamin B12 absorption and malabsorption. JF Gut JO Gut FD BMJ Publishing Group Ltd and British Society of Gastroenterology SP 1686 OP 1691 DO 10.1136/gut.30.12.1686 VO 30 IS 12 A1 H Schjønsby YR 1989 UL http://gut.bmj.com/content/30/12/1686.abstract AB