Sources, Bioavailability, and Safety of Silicon Derived from Foods and Other Sources Added for Nutritional Purposes in Food Supplements and Functional Foods

Silicon is a microelement that performs a number of important functions in the human body, being involved in the formation and maintenance of normal osteocartilaginous connective tissue, such as skin, hair, and nails, and having beneficial effects in the prevention of cardiovascular and neurodegenerative diseases. Natural sources of silicon include fruits, vegetables, cereals, and mineral water. European and North American diets are generally low in silicon, which correlates with a diet high in processed foods. Dietary silicon deficiency can be overcome by the consumption of high bioavailability silicon-rich foods and the use of silicon supplements. A good form of supplementation is orthosilicic acid (OSA), usually stabilized by the introduction of a methyl group, choline, or vanillin. OSA is naturally found in diatomaceous earth in the form of amorphous silica and extracts from silicon-rich plants, e.g., horsetail (Eguiseti herbaL.) and nettles (Urtica dioicaL.). This article presents the characteristics of the various sources of silicon and their bioavailability and safety of use, with particular reference to the sources used in functional foods and dietary supplements. There is a great need to produce functional foods containing dietary silicon, together with other scarce mineral components.