Minerals are inorganic substances that have no energy value and that are needed by the body to function correctly. Some are required in large quantities, such as one or more grams per day (e.g. calcium). Others are required in lesser amounts, i.e. one or more micrograms or milligrams per day (e.g. iron); these are so-called oligo-elements or trace elements. Our body uses minerals for many different functions, such as keeping the bones, muscles, heart and brain working properly. Minerals are also important for making enzymes and hormones.