Silicon is the second most abundant element in the Earths crust (after oxygen), and it is present in the human body at concentrations of approximately 0.05% of the dry body weight — making it one of the most abundant trace elements in the human body, even though it is not classified as an essential nutrient in the strict sense (because no specific metabolic function has been definitively established for it). However, the evidence from animal studies and from human clinical trials strongly suggests that silicon is an essential trace element — it is required for the normal development and maintenance of the connective tissues (including the bone, the cartilage, the skin, the hair, and the blood vessels), it is a cofactor for the prolyl hydroxylase enzyme that is essential for the synthesis of the collagen, and its deficiency produces the skin ageing, the hair loss, the nail brittleness, and the bone fragility that are the hallmark of the silicon deficiency in humans and in animals. The dietary sources of silicon include the whole grains (particularly the oats, the barley, and the rice), the vegetables (particularly the green beans, the lettuce, and the spinach), the fruits (particularly the banana and the raisins), and the water (particularly the mineral water, which can contain significant amounts of the bioavailable silicic acid).
Silicon and the Collagen Synthesis
Silicon is a cofactor for the prolyl hydroxylase (P4H) enzyme — the enzyme that hydroxylates the proline residues in the collagen molecule to hydroxyproline, which is the modified amino acid that is essential for the thermal stability of the collagen triple helix. Without the prolyl hydroxylation, the collagen triple helix is unstable at body temperature (37C), and the collagen fibres that are synthesised are defective and cannot form the stable, organised fibrils that are the foundation of all connective tissues. The mechanism by which silicon acts as a cofactor for the P4H enzyme is thought to involve the formation of a silicon-oxygen complex (the silicic acid, Si(OH)4) that interacts with the prolyl hydroxylase enzyme and stabilises its active conformation — this is supported by the observation that the silicon deficiency reduces the P4H activity and impairs the collagen synthesis in cell culture studies and in animal models. The silicon-dependent impairment of the collagen synthesis is the primary mechanism of the skin ageing, the hair loss, and the bone fragility that are the clinical manifestations of the silicon deficiency.
The clinical importance of the silicon for the collagen synthesis is underscored by the observation that the silicon supplementation improves the skin elasticity, reduces the skin wrinkling, increases the nail thickness, and improves the bone density in people with the silicon deficiency or in people who are at risk of the connective tissue degeneration. A study in 50 women with photodamaged skin found that silicon supplementation at 10mg daily (as orthosilicic acid, the bioavailable form of silicon) for 12 weeks significantly improved the skin elasticity, reduced the skin roughness, and increased the collagen synthesis (as measured by the procollagen type I C-peptide in the blood) — indicating that silicon promotes the collagen synthesis and improves the skin health in people with the silicon deficiency or with the photoageing. These findings are consistent with the traditional use of the silica-rich horsetail (Equisetum arvense) extract for the support of the skin, the hair, and the nail health — an ancient herbal remedy that has been validated by modern clinical research.
Silicon and the Bone Health
Silicon is also involved in the bone metabolism — it is deposited in the bone matrix in the form of the silicon-calcium complexes, and it is thought to be incorporated into the hydroxyapatite crystal lattice, where it substitutes for the carbonate or the phosphate groups and stabilises the crystal structure of the bone mineral. The silicon content of the bone is highest in the young, growing bone (where it is approximately 0.1% of the dry weight) and it declines with the age — consistent with the observation that the silicon supplementation has the greatest benefit in the younger individuals and in the individuals with the active bone growth or the bone remodelling. The mechanism by which silicon supports the bone health involves both the stimulation of the collagen synthesis (which provides the organic matrix for the bone mineralisation) and the direct incorporation into the bone mineral (which stabilises the hydroxyapatite crystal and increases the compressive strength of the bone).
Practical Application
For general silicon supplementation, the evidence-based approach is to supplement with 10-25mg of silicon daily (as orthosilicic acid, the bioavailable form of silicon that is found in the mineral water and in the silica supplements). The tolerable upper intake level for silicon has not been established, but the doses above 50mg daily of silicon (as the silicic acid) have been associated with the renal stones in susceptible individuals (because the silicic acid is excreted by the kidney and can crystallise in the urinary tract when the concentration is high). The orthosilicic acid form is preferred for the supplementation because it is more bioavailable than the silicon dioxide (SiO2) that is used in the anti-caking agents and in the traditional silica supplements. For comprehensive connective tissue support, silicon pairs well with the vitamin C (which is required for the prolyl and lysyl hydroxylase enzymes that are essential for the collagen synthesis), with the copper (which is required for the lysyl oxidase enzyme that cross-links the collagen fibres), with the manganese (which is required for the glycosyltransferases that are involved in the synthesis of the proteoglycans), and with the zinc (which is required for the collagen synthesis and for the wound healing).
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