Vitamin B12 is an essential part of keeping nerve and blood cells healthy, reports the National Institutes of Health. Most adults do not need B12 supplementation because they get enough through the food they eat as part of a balanced diet.
Clams and beef liver are the best foods for B12, according to the NIH. Dairy products, eggs, poultry, fish and other forms of meat are also good sources. In addition, certain grain products, such as bread and breakfast cereals, are fortified with the vitamin. Fortified products are indicated on their labels.
People who have trouble absorbing enough vitamin B12 from food may have an underlying health problem, such as celiac or Crohn's disease. Senior citizens may have trouble because their stomachs do not have enough hydrochloric acid, which is necessary for digesting the nutrient. People over age 50 should take dietary supplements or eat fortified foods to ensure they get enough, as suggested by the NIH.
Low levels of vitamin B12 are associated with a form of anemia called megaloblastic anemia, according to the NIH. It also can cause other symptoms, including weakness, fatigue and depression. Some people may feel a tingling sensation or numbness in their extremities. Megaloblastic anemia can cause cognitive impairment, such as confusion and memory problems. Some people need prescription vitamin B12 injections to treat the deficiency.