**1. Introduction**

Vitamin B12 is only synthesized by microorganisms in nature and thus, is obtained by human beings through their diet [1]. Since the most important source of vitamin B12 is animal proteins, vegetarians may lack sufficient quantities of this vitamin in their diets.

Vitamin B12 deficiency may be caused by a lower dietary intake (impaired absorption or decreased intake), an autoimmune issue related to intrinsic factors or gastrointestinal system diseases resulting in vitamin B12 malabsorption [2]. The most important symptoms and findings of severe vitamin B12 deficiency are anemia and neurological problems. Vitamin B12 deficiency is one of the most common causes of macrocytic anemia [3, 4]. If it is not treated, anemia symptoms and neurological disturbances resulting in spinal cord and cerebral cortex demyelination may emerge [5].

Epidemiology concerns health and disorders, etiological agents, the symptoms of disorders, diagnoses and the benefits of clinical care, and its discontinuation. Determining risk factors and at‐risk groups as well as educating them about vitamin B12 deficiency, proper diet, and replacement would prevent any irreversible complications of this type of deficiency. The goal of this study is to review epidemiological studies related to vitamin B12 deficiency and to point out the importance of identifying and treating it.
