Vitamin B12 is a nutrient that is necessary for keeping the body's nervous system and blood cells healthy. It also helps to produce essential DNA in every cell. It is needed to prevent a type of anemia, called megaloblastic anemia, which causes tiredness and weakness, according to the Office of Dietary Supplements at the National Institutes of Health.
According to the Office of Dietary Supplements, about 1.5 to 15 percent of Americans suffer from a deficiency of vitamin B12. Symptoms of a vitamin B12 deficiency can include loss of appetite, constipation and weight loss. Infants with a vitamin B12 deficiency can exhibit signs of failure to thrive, and face developmental delays in reaching the typical milestones. These infants may experience problems with movement and the development of megaloblastic anemia. A doctor can perform routine test to check vitamin B12 levels and detect any deficiencies.
The Office of Dietary Supplements states that symptoms of vitamin B12 deficiency can happen even in people who do not show signs of anemia. Symptoms in the nervous system of vitamin B12 deficiency include numbness and tingling in the hands and feet. Other symptoms can involve poor memory, depression, confusion, dementia, loss of balance and soreness of the mouth and tongue.