Vitamin B12 does more than build red blood cells and prevent anemia. It is needed for healthy functioning of the brain and nerves, and helps the body metabolize fats, proteins, and carbohydrates. In some people, especially those over age 50, the body does not produce sufficient "intrinsic factor," a component of stomach acid required for absorbing vitamin B12. Likewise, vitamin B12 is poorly absorbed by people who suffer digestive disorders, such as Crohn's or celiac disease, and people who have had gastrointestinal surgery. Vegetarians and vegans can also receive too little vitamin B12 since the main dietary sources of B12 are meat and cheese.
