Vitamin B12 is an essential water-soluble nutrient for the normal function of several body systems, including the cardiovascular, nervous, and digestive systems. Diet choices and certain prescription drugs, like metformin, can induce a B12 deficiency. If you have a vitamin B12 deficiency, you may feel tired or weak. Taking a Vitamin B12 supplement may benefit your body in impressive ways, such as by boosting your energy, improving your memory, and helping prevent heart disease. Quantity: 90 servings.