B-12 is a water-soluble vitamin that plays an essential role in red blood cell formation, cell metabolism, nerve function, and the production of DNA. B-12 may prevent anemia, improve energy levels, and promote a good sleep schedule as it helps in the making of red blood cells. Food sources of vitamin B-12 include poultry, meat, fish, and dairy products. Vitamin B-12 is also added to some foods, such as fortified breakfast cereals, and is available as an oral supplement. Some people have trouble absorbing vitamin B12 from food.