Vitamin B12, also known as cobalamin is a member of the B vitamin family which your body uses to build red blood cells. Red blood cells carry oxygen and nutrients to our muscles. It also helps break down proteins, fats, and carbohydrates, serving a vital role in maintaining the body s energy supply. For this reason, people suffering from low vitamin B12 often complain of fatigue and weakness. Additionally, Vitamin B12 has been known to: