B12 defiency can cause anorexia?

Generally not but if. B12 deficiency is relatively common and if mild, often cause no symptoms. If deficiency is chronic and more severe, anemia may develop, fatigue, irritability, and nerve damage may occur. Severe deficiency can lead to dementia as well. Any of these condition, if severe, can cause secondary etc. B12 is an important vitamin and treatment is relatively easy/inexpensive. Consult your doc. Good luck.