B vitamins play crucial roles as coenzymes in the nervous system. Vitamin B1 (thiamine), B6 (pyridoxine), and B12 (cobalamin) contribute essentially to the maintenance of a healthy nervous system. Even mild deficiency of B12 has been shown to accelerate cognitive decline. Vitamin B12 is involved in the function and development of the brain, nerve cells, the myelin sheaths that protect nerves, and blood cells. Vitamin B12 is sometimes taken to treat memory loss, poor concentration, and Alzheimer’s disease and to boost your mood or energy levels.