Trace element nutrition and bone metabolism.

Many of the trace elements which have essential roles in animals, such as zinc (Zn), manganese (Mn) and copper (Cu), are required for the growth, development and maintenance of healthy bones (Rucker, 1988; Leach, 1988). Of the remaining trace or ultratrace elements, which by definition are normally present at low concentrations in animal tissues, some have a toxic effect on bone such as lead (Pb) and cadmium (Cd), and others have either low toxicity or have not been studied in any detail. At high concentrations, essential trace elements can also affect bone metabolism with harmful consequences but, rarely, a trace element can induce apparently beneficial effects at pharmacological doses. For example, fluoride (F) therapy increases bone density in patients with advanced osteoporosis. For some trace elements such as boron (B) and molybdenum (Mo), the evidence for a direct effect on bone, be it essential or toxic, is not conclusive at this time.