**4. The clinical spectrum of vitamin B12 deficiency**

Both vitamin B12 deficiency and folate deficiency cause megaloblastic anemia. In fact, only vitamin B12 deficiency causes neuorological change. Additionally, the difference between these two anemia types is the duration between the start of deficiency and symptoms being apparent. The symptoms of B12 deficiency appear within years after the removal of vitamin B12 from the diet whereas the symptoms of folate deficiency are seen within 4‒6 weeks.

Vitamin B12 deficiency is one of the most frequent vitamin deficiencies worldwide [7]. So, this deficiency is an extremely important public health issue owing to its serious complications if it is not detected and treated appropriately. Epidemiological studies in this field are, therefore, of great value. There are many epidemiological studies related to vitamin B12 deficiency, which have used different methods and evaluated different disorders accompanying it [8, 9].
