Vitamin B12 helps to maintain the proper metabolism of protein, fat and carbs. Stacker 2 10,000% RDA Four Count Blister Pack New Factory Sealed. Vitamin B12 is a water-soluble vitamin that keeps your nerves and red blood cells healthy. It is responsible for the smooth functioning of several critical body processes. It is possible for the body to develop a vitamin B12 deficiency. This deficiency is usually reported with symptoms of fatigue.