Silicon, aluminium, arsenic and lithium: essentiality and human health implications.

Ultratrace elements are currently being studied to determine their nutritional significance and impact on health, taking into account their possible toxic effects. Some elements are essential to one or more specific biological functions in humans while other are nonessential. Nevertheless, the latter may produce desirable pharmacological effects or, on the contrary, possess harmful properties which depend on the inherent toxic potential of the element, the amount ingested and the intrinsic characteristics of the individual. This review updates the information on the essentiality and toxicological aspects of silicon, aluminium, arsenic, and lithium and considers the involvement's in degenerative diseases, such as cardiovascular diseases, osteoporosis and Alzheimer's disease. Silicon and lithium are protective while aluminium and arsenic have toxic effects.