Usually, the human body stores enough vitamin B12 in the body and hence, the symptoms of deficiency may not appear until it is severe. The common signs of vitamin B12 deficiency include: Megaloblastic anaemia (the red blood cells become larger than normal and do not function properly) Fatigue Pale skinHeart palpitations Frequent headaches  Loss of appetite Constipation  Weight loss Sore, inflamed tongue with mouth ulcers Numbness or tingling sensation in the hands and feet (indicating nerve damage) Vision problems Difficulty in walking and maintaining balance  Infertility Confusion