Silicon (Si) is the most abundant
element present in the Earth's crust besides
oxygen. However, the exact biological roles of
silicon remain unknown. Moreover, the ortho-
silicic acid (H4SiO4), as a major form of bioavailable
silicon for both humans and animals, has not been given adequate attention so far.
Silicon has already been associated with bone mineralization,
collagen synthesis, skin, hair and nails health
atherosclerosis,
Alzheimer disease, immune system enhancement, and with some other disorders or pharmacological effects. Beside the ortho-
silicic acid and its stabilized formulations such as
choline chloride-stabilized ortho-
silicic acid and
sodium or
potassium silicates (e.g. M2SiO3; M= Na,K), the most important sources that release ortho-
silicic acid as a bioavailable form of
silicon are: colloidal
silicic acid (
hydrated silica gel),
silica gel (amorphous
silicon dioxide), and
zeolites. Although all these compounds are characterized by substantial water insolubility, they release small, but significant, equilibrium concentration of ortho-
silicic acid (H4SiO4) in contact with water and physiological fluids. Even though certain pharmacological effects of these compounds might be attributed to specific structural characteristics that result in profound adsorption and absorption properties, they all exhibit similar pharmacological profiles readily comparable to ortho-
silicic acid effects. The most unusual ortho-
silicic acid-releasing agents are certain types of
zeolites, a class of aluminosilicates with well described ion(
cation)-exchange properties. Numerous biological activities of some types of
zeolites documented so far might probably be attributable to the ortho-
silicic acid-releasing property. In this review, we therefore discuss biological and potential
therapeutic effects of ortho-
silicic acid and ortho-
silicic acid -releasing
silicon compounds as its major natural sources.