A healthy nervous system is dependent on B12 and folate, which perform several important functions in the body. The following problems can be caused by a deficiency in either of these vitamins: Extreme fatigue Low physical energy There is a feeling of pins and needles in the arms (paraesthesia) Tongue that is sore and red A sore mouth or ulcers of the mouth Weakness in muscles An inability to see clearly Depression, anxiety, or confusion Memory, understanding, and judgment problems