The incidence of clinically recognisable, acute dietary deficiency states is extremely rare for most essential minerals. Chromium responsive symptoms of reduced insulin response have been reported in isolated cases of patients undergoing long-term TPN where their infusion solution was not supplemented with chromium. Chromomodulin stimulates the activity of this tyrosine kinase and is necessary for a normal response to insulin. Copper has clearly been established as an essential nutrient but overt deficiency of the mineral is rarely seen. Experimental copper deficiency has been induced in animals and it results in anaemia, low neutrophil count, osteoporosis and skeletal abnormalities. It is generally agreed that fluoride is not strictly an essential nutrient but that it can be a beneficial dietary substance that reduces the risk of dental decay especially if consumed in optimal amounts by young children. Phosphorylation and dephosphorylation reactions are an important feature of biochemical reactions.