Vitamin B12 Deficiency (Pernicious Anemia) By Larry E Johnson, MD, PhD, University of Arkansas for Medical Sciences Reviewed / Revised Nov 2022 View Patient Education Etiology Symptoms and Signs Diagnosis Treatment Key Points Topic Resources Causes of Vitamin B12 Deficiency Dietary vitamin B12 deficiency usually results from inadequate absorption, but deficiency can develop in vegans who do not take vitamin supplements.