Any of a number of elements required by living organisms to ensure normal growth, development, and maintenance (greater than 0.005%),are calcium, phosphorus, potassium, sodium, chlorine, sulphur and magnesium.

The trace elements occur at much lower concentrations and thus requirements are much less. The most important are iron, manganese, zinc, copper, iodine, cobalt, selenium, molybdenum, chromium, and silicon.

Each element may fulfill one or more of a variety of metabolic roles.