silicic acid

Annual mean sea surface silicic acid for the World Ocean. Data from the World Ocean Atlas 2005.

Silicic acid is a general name for a family of chemical compounds of the element silicon, hydrogen, and oxygen, with the general formula [SiO_x(OH)_4-2x]_n.^[1][2] Some simple silicic acids have been identified in very dilute aqueous solution, such as metasilicic acid (H₂SiO₃), orthosilicic acid (H₄SiO₄, pK_a1=9.84, pK_a2=13.2 at 25°C), disilicic acid (H₂Si₂O₅), and pyrosilicic acid (H₆Si₂O₇); however in the solid state these probably condense to form polymeric silicic acids of complex structure.

Silicic acids may be formed by acidification of silicate salts (such as sodium silicate) in aqueous solution. When heated they lose water to form silica gel, an active form of silicon dioxide.

In the oceans, silicon exists primarily as orthosilicic acid (H₄SiO₄), and its biogeochemical cycle is regulated by the group of algae known as the diatoms.^[3][4] These algae polymerise the silicic acid to so-called biogenic silica, used to construct their cell walls (called frustules).

Continuing research of the correlation of aluminium and Alzheimer's disease has in the last few years included the use of silicic acid in beverages^[5][6][7], due to its abilities to both reduce aluminium uptake in the digestive system as well as cause renal excretion of aluminium.

Orthosilicic acid is the form predominantly absorbed by humans and is found in numerous tissues including bone, tendons, aorta, liver and kidney. Compelling data suggest that silica is essential for health although no RDI has been established. However, deficiency induces deformities in skull and peripheral bones, poorly formed joints, reduced contents of cartilage, collagen, and disruption of mineral balance in the femur and vertebrae. ^[8]

Choline-stabilized orthosilicic acid is bioavailable nutritional supplement. It has been shown to stimulate collagen type 1 synthesis and osteoblastic differentiation in human osteoblast-like cells in vitro^[9], improve hair tensile strength^[10], have positive effect on skin surface and skin mechanical properties, and on brittleness of hair and nails^[11], abate brittle nail syndrome^[12], partially prevent femoral bone loss in the aged ovariectomized rat model^[13], increase collagen concentration in calves ^[14], and have potential beneficial effect on bone collagen formation in osteopenic females^[15].

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