Silicon is the second-most abundant element in the earth's crust, after oxygen. It binds to oxygen, forming crystalline or amorphous silica (silicon dioxide, SiO2), silicic acid (Si(OH)4), and silicates, such as quartz. Silicon is present in rocks, soil, sand, and dust as crystalline silica. Silicic acid is formed naturally from silica and is readily absorbed in the human gastrointestinal tract.
Silicon is an ultratrace element, meaning that it is suspected as being required in quantities of less than 1 milligram, but is associated with no known essential role in biological processes. A recommended dietary allowance (RDA) or adequate intake (AI) has not been established for silicon.
In the diet, silicon is found mainly in drinking water and plant-based foods, such as beer, unrefined grains (oats, barley, rice, and wheat bran), fruits, vegetables (spinach), and beans (red lentils).
Silicon is included as silicates in cosmetic and pharmaceutical preparations. Silicates are also added to processed foods and beverages, where they serve as anticaking agents, thickeners, and stabilizers, and they are used as clarifying agents in beer and wine.
Silicon is biocompatible and has been used in many implantable medical devices, including pacemakers, defibrillators, stents, materials for plastic and reconstructive surgery (including breast implants and bone grafts), devices for sustained-release delivery of drugs, sheeting (to treat and prevent the formation of scars following surgery), and liner sockets, or sleeves (to attach prostheses after amputation).
Although researchers have examined the use of silicon for various purposes, its use for reducing aluminum toxicity associated with Alzheimer's disease is controversial. Some evidence suggests that silicon may be essential in humans for bone growth and health and development of other tissues in the body. High-quality scientific evidence supporting the use of silicon to treat any condition in humans is lacking.

Related Terms

Aluminum silicate, amorphous silica, attapulgite, bentonite, calcium silicate, crystalline silica, diatomite, fuller's earth, hectorite, kaolin, lithium magnesium silicate, lithium magnesium sodium silicate, magnesium aluminum silicate, magnesium silicate, magnesium trisilicate, monomeric silicic acid, monosilicic acid, montmorillonite, orthosilicic acid, pyrophyllite, quartz, SiO2, Si(OH)4, silicate, silicic acid, sodium magnesium silicate, zeolite, zirconium silicate
Note: This monograph does not cover silicon-based manufactured materials, including microelectronics and biomedical devices and materials.

evidence table

These uses have been tested in humans or animals. Safety and effectiveness have not always been proven. Some of these conditions are potentially serious, and should be evaluated by a qualified healthcare provider.
Alzheimer's dementia (Grade: C)
Preliminary studies suggest that dietary silicon supplementation may reduce aluminum absorption and prevent or reduce aluminum accumulation in tissues. It has been proposed that this may be useful in preventing or reducing aluminum accumulation in the brain in Alzheimer's disease. Additional research is needed before a conclusion can be made.
Brittle fingernails (Grade: C)
Daily doses of 10 milligrams of silicon or 10 milliliters of colloidal silica have been used effectively to treat brittle nail syndrome. Additional research is required in this area.
Growth (bone health and development) (Grade: C)
Evidence suggests that silicon is involved in bone and collagen mineralization. Limited studies have demonstrated an association between silicon intake and bone mineral density.