Vitamin B12 helps make red blood cells. It helps in keeping the nervous system healthy. Not just that, Vitamin B12 is needed for brain function and also helps make DNA, the genetic material in all cells. Lack of Vitamin B12 can lead to Pernicious Anemia, a blood condition that makes people weak and tired. Vitamin B12 keeps the protective cover around nerves; and not having enough B12 can cause nerve damage. Experts explain the importance of Vitamin B12.