Giardia infection causes vitamin B12 deficiency.

A patient presented with hematological evidence of vitamin B12 deficiency. The Schilling test performed suggested intestinal malabsorption and further investigation revealed heavy infestation with Giardia lamblia. Specific treatment of the giardiasis with tinidazole resulted in correction of the abnormalities in vitamin B12 absorption. These findings, together with the absence of other causes of vitamin B12 deficiency, suggest that giardiasis should be considered as a cause of vitamin B12 deficiency.