Si – Silica is found in igneous rocks at 281,500 ppm; shale at 73,000 ppm; sandstone at 368,000 ppm; limestone at 24,000 ppm*1 fresh water at 6.5 ppm; sea water at 3 ppm; soils at 330,000 ppm (found as Si02, the most abundant form of Si in nature, in silicates and clays); marine plants at 1,500 to 20,000 ppm; accumulated by diatoms, horsetail, ferns, Cyoeraceae, Graineae and juncaceae and by the flowers of Pappophorum silicosum; marine animals at 70,000 ppm; land animals at 120 to 6,000 PPM (highest levels in hair, lungs and bone).
Silicon supplementation increases the collagen in growing bone by 100 %. Tissue levels of Si decrease with aging in unsupplemented humans and laboratory species. Silica deficiency is characterized by dry brittle hair, brittle fingernails and toenails, poor skin quality, poor calcium utilization and arterial disease. High fiber diets contain lots of Si, which leads many investigators to think that Si helps to lower cholesterol. The recommended intake of Si ranges from 200 to 500 mg/day.
Silicon is the second most common element on the surface of the Earth and widely distributed in plant food and water. Silicon occurs in the skin, bone and connective tissue of animals. It is an essential nutrient in animals, required for normal skeletal development of rats and chicks, for example. It seems probable that silicon is essential for humans, though this remains to be established. No Recommended Dietary Allowance has been established for silicon. Silicon participates in the formation of connective tissue where it forms complexes between protein and acidic polysaccharide complexes. Acidic polysaccharides (glycosaminoglycans) contribute to the gelatinous material that holds cells together. In humans, the silicon content of the aorta, the skin and the thymus decreases with age.
Silicon is widely distributed in whole grains, organ meats like liver, and red meat. Most of the silicon of whole grains is lost when white flour is prepared, and highly processed foods contain little silicon. The typical diet supplies approximately 1 g per day. Within the confines of the typical diet, silicon is nontoxic.
Silicon, as the second most abundant element in the earth’s crust, is not found free in nature, but occurs chiefly as the oxide and silicates. Asbestos, tremolite, the feldspars, clays and micas are but a few of the silicate minerals.
The essential function of silicon has been independently demonstrated by two groups of researchers in two species of experimental animals. Growth stimulation of rats following administration of silicon was observed only when low-silicon (< 5 ug of silicon/g of diet) synthetic rations based on crystalline amino acids were fortified with 250-500 Mg of silicon/g of diet. However, regardless of dietary composition, all other experiments in which silicon deficiency has been induced have demonstrated the importance of the element for the normal development of connective tissue and bone in chickens and rats. Deficiency always produced deformities of skull and peripheral bones, characterized by poorly formed joints, defective endochondral bone growth and reduced contents of articular cartilage, hexosamine, collagen and water.
Silicon & bone
Silicon’s mode of action is related to the formation of bone, possibly by the following two mechanisms: 1) by facilitating the formation of glycosaminoglycan and collagen components of the bone matrix through its role as a constituent of the enzyme proly1hydroxylase, 2) by a structural role for silicon as a component of glycosaminoglycans and glycosamino-protein complexes in which it is believed to occur as silanolate in mucopolysaccharides, linking different polysaccharides in the same polysaccharide chain, or linking acid mucopolysaccharides to protein. The postulated structures of such links have still to be identified.
Silicon can be detected in small areas of ossifying bone during the early stages of mineralization. The silicon content of young osteoid tissue increases markedly, together with that of calcium, but at more advanced stages of bone formation, when calcification sets in, the silicon content decreases again to trace levels. The element is located within the mitochondria of the osteoblast.
Silicon & arteries
It has been shown that silicon concentrations in human arteries decrease with increasing age and with the onset of atherosclerosis, and that a combination of large intravenous and oral doses of silicon reduces the incidence and severity of atherosclerosis in cholesterol-fed rabbits. Several reports have independently confirmed a decline in silicon with age in some animal tissues, but its causes and possible relevance to the aging process remain unknown.
The general manifestations of silicon toxicity are collectively described as silicosis. As with other essential elements, certain chemical forms of silicon are toxic if inhaled or ingested in large amounts. The carcinogenic effects of asbestos fibers have caused serious public health problems where some forms of asbestos have been used extensively in construction projects in the past. Urolithiasis from the consumption of high-silicon forages is well known in cattle and sheep in several areas of the world. In contrast, few cases of siliceous calculi have been reported in human beings.
Foods of plant origin contain more silicon than those of animal origin. Whole grasses and cereals may contain 3-6% as silica. The silicon intake of adults in Finland, the United Kingdom, and the USA varies between 21 and 49 mg/day. Fruits and most animal products contribute little silicon, whereas most foods of vegetable origin contain the element in amounts roughly proportional to their fiber content. The factors governing the biological availability of silicon have not been adequately defined.
While silicon has been shown to play an essential role in the development of bone in two species of experimental animal, for which a requirement of 100-250 ug/g of diet has been suggested, no data are available from which human requirements for silicon can yet be estimated.
Silicon in humans
Connective tissues such as the aorta, trachea, tendon, bone, skin, and its appendages are unusually rich in silicon, as shown by studies in several animal species (Carlisle, 1974). In the rat the aorta, trachea, and tendon are four to five times richer in silicon than liver, heart, and muscle.
Among the human tissues, epidermis and hair have been reported to contain unusually large amounts of localized silicon. The element accumulates in the cornified epidermis on the surface of skin and in the epicuticle of hair as well as the wool and feathers of other animals in an alkali-insoluble component constituting only 0.4-1.7% of the total tissue weight. It has been suggested (Fregert, 1959) that this small alkali-insoluble component with its high silicon content may contribute to the solidity and great chemical resistance of keratinous tissues and may also play a role as a barrier of absorption. High silicon levels have also been reported in human dental enamel (Losee et al., 1973) and in the head of the monkey femur containing the epiphyses (Le Vier, 1975).
The high silicon content of connective tissues appears to arise mainly from its presence as an integral component of the glycosaminoglycans and their protein complexes that contribute to the structural framework of this tissue. Fractionation procedures reveal that connective tissues, such as bone, cartilage, and skin, yield complexes of high silicon content. Silicon is also found as a component of glycosaminoglycans isolated from these complexes.
The consistently low concentrations of silica in most organs do not appear to vary appreciably during life. Parenchymal tissue, such as heart and muscle, for example, ranges from 2 to 10 u of silicon/g dry weight (Carlisle, 1982).
Selected reported deficiency signs
Skull structure abnormalities associated with depressed collagen content in bone of rats and chicks; long bone abnormalities in chicks characterized by small, poorly formed joints, defective endochondral growth, and depressed contents of articular cartilage, water, hexosamine, and collagen; depressed ash, calcium, magnesium, and phosphorus concentrations in tibias and skulls of calcium deficient rats; decreased brain zinc content in thyroidectomized, aluminum-supplemented rats.
A biological cross-linking agent for macromolecules (e.g., phosphorylated glycoproteins such as osteonectin) involved in the initiation of cartilage calcification and the regulation of crystal growth.
Dietary need and sources
Human requirement may be in the range of 5 to 20 mg/day; rich food sources include unrefined grains of high fiber content, cereal products, and root vegetables.
Biol Trace Elem Res 1992 Aug;34(2):185-195
Silicon metabolism. The interrelations of inorganic silicon (Si) with systemic iron (Fe), Zinc (Zn), and copper (Cu) pools in the rat.
Najda J, Gminski J, Drozdz M, Danch A
Department of Biochemistry and Chemistry, Silesian Medical Academy, Medykow, Poland.
The influence of silicon treatment on the levels of trace elements zinc (Zn), copper (Cu), and iron (Fe) in serum and tissues was studied in rats. The concentrations of silicon, iron, and zinc were estimated in samples of sera and tissues of rats receiving per mouth a soluble, inorganic silicon compound–sodium metasilicate nonahydrate (Na2SiO3.9H2O), dissolved in the drinking water. An increase of copper concentrations in liver and aortic walls in the experimental group was observed, with simultaneous reduction of zinc amounts in serum and all the tissue samples in the course of the experiment. The iron concentrations in the analyzed samples did not show any significant changes between both groups. The silicon levels in serum and in all the examined tissues were significantly higher in the tested group. The results provide evidence for the silicon interaction with copper and zinc, which could result in a number of metabolic process modifications, antiatheromatous activity among them.
Ciba Found Symp 1986;121:123-139
Within the last decade silicon has been recognized as participating in the normal metabolism of higher animals and as being an essential trace element. Silicon is found to perform an important role in connective tissue, especially in bone and cartilage. Bone and cartilage abnormalities are associated with a reduction in matrix components, resulting in the establishment of a requirement for silicon in collagen and glycosaminoglycan formation. Silicon’s primary effect in bone and cartilage is on the matrix, with formation of the organic matrix appearing to be more severely affected by silicon deficiency than the mineralization process. Additional support for silicon’s metabolic role in connective tissue is provided by the finding that silicon is a major ion of osteogenic cells and is present in especially high concentrations in the metabolically active state of the cell; furthermore, silicon reaches relatively high levels in the mitochondria of these cells. Further studies also indicate that silicon participates in the biochemistry of the subcellular enzyme-containing structures. Silicon also forms important interrelationships with other elements. Although it is clear from the body of recent work that silicon performs a specific metabolic function, a structural role has also been proposed for it in connective tissue. A relationship established between silicon and aging probably relates to glycosaminoglycan changes.
Sci Total Environ 1988 Jul 1;73(1-2):95-106
Silicon as a trace nutrient.
School of Public Health, University of California, Los Angeles 90024.
Silicon performs an important role in connective tissue, especially in bone and cartilage. Silicon’s primary effect in bone and cartilage appears to be on formation of the organic matrix. Bone and cartilage abnormalities are associated with a reduction in matrix components, resulting in the establishment of a requirement for silicon in collagen and glycosaminoglycan formation. Additional support for silicon’s metabolic role in connective tissue is provided by the finding that silicon is a major ion of osteogenic cells, especially high in the metabolically active state of the cell. Further studies also indicate that silicon participates in the biochemistry of subcellular enzyme-containing structures. Silicon also forms important relationships with other elements. Although it is clear from the body of recent work that silicon performs a specific metabolic function, a structural role has been proposed for silicon in connective tissue. A relationship established between silicon and aging probably relates to glycosaminoglycan changes.
Lancet 1977 Feb 26;1(8009):454-457
A logical argument can be made for the hypothesis that lack of silicon may be an important etiological factor in atherosclerosis. As silicic acid or its derivatives, silicon is essential for growth. It is found mainly in connective tissue, where it functions as a cross-linking agent. Unusually high amounts of bound silicon are present in the arterial wall, especially in the intima. Various kinds of dietary fiber have been reported to be effective in preventing experimental models of atherosclerosis, reducing cholesterol and blood-lipid levels, and binding bile acids in vitro. Exceptionally large amounts of silicon (1000 to 25 000 p.p.m.) were found in fiber products of greatly varying origin and chemical composition which were active in these tests. Inactive materials, such as different types of purified cellulose, contained only negligible quantities of the element. It is concluded that silicate-silicon may be the active agent in dietary fiber which affects the development of atherosclerosis. Two out of three samples of bran also had relatively low levels, which could explain why bran does not lower serum-cholesterol. The fact that atherosclerosis has a low incidence in less developed countries may be related to the availability of dietary silicon. Two instances are presented where silicon is reduced by industrial treatment: white flour and refined soy products were much lower in silicon than–their respective crude natural products. The chemical nature of silicon in different types of fiber is not known. It could exist as orthosilic acid, polymeric silicic acid, colloidal silica (opal), dense silica concentrations, or in the form of organically bound derivatives of silicic acid (silanolates). Possible mechanisms of action are discussed.
Med Hypotheses 1997 Aug;49(2):175-176
Reported antiatherosclerotic activity of silicon may reflect increased endothelial synthesis of heparan sulfate proteoglycans.
Nutrition 21, San Diego, CA 92109, USA.
Silicon plays a physiologically essential but mechanistically obscure role in promoting the synthesis of mucopolysaccharides and collagen. In light of reports that increased silicon ingestion impedes cholesterol-induced atherogenesis in rabbits and may be associated epidemiologically with reduced cardiovascular risk, it is reasonable to speculate that supplemental silicon may stimulate endothelial production of heparan sulfate proteoglycans that inhibit intimal hyperplasia.
Silicon & Aging
Connective tissue changes are prominent in aging so that it is not surprising to find a relationship between silicon and aging in certain tissues. The silicon content of the aorta, other arterial vessels, and skin was found to decline with age, in contrast with other analyzed tissues, which showed little or no change (Carlisle, 1974). The decline in silicon content was significant and was particularly dramatic in the aorta, commencing at an early age. This relationship occurred in several animal species, including the rabbit, rat, chicken, and pig. For example, in the rabbit between 12 weeks and 18-24 months of age there was a decrease of silicon in the aorta of 84% and in the skin of 83%. In the pig, the silicon content of mature pigskin decreased 90%, compared with fetal pigskin. During fetal development silicon was shown to increase with age.
Leslie et al. (1962) also found a decrease in silicon content in rat skin with age, in contrast to other tissues analyzed that showed an increase, such as brain, liver, spleen, lung, and femur. The increase seen in the lung is probably due to dust inhalation. In muscle and tendon, no significant changes in silicon were found. In skin, there was a 60% decrease between 5 weeks and 30 months. The dermis samples of the 30-month-old rat contained less silicon than the corresponding whole skin.
Similarly, in human skin, the silicon content of the dermis has been stated to diminish with age (MacCardle et al., 1943). It has also been reported by French investigators (Loeper et al., 1966; 1978) that the silicon content of the normal human aorta decreases significantly with age, in contrast to earlier findings (Kvorning, 1950), and, furthermore, that the level of silicon in the arterial wall decreases with the development of atherosclerosis. The possible involvement of silicon in atherosclerosis has also been suggested by others (Schwarz, 1978; Dawson et al., 1978). Of possible significance here, a relationship has been reported (Charnot and Nres, 1971) between silicon, age, and endocrine balance as a result of finding changes in absorption and resulting levels of silicon in the blood and intestinal tissues of rats in relation to age, sex, and various endocrine glands. It is suggested that the decline in hormonal activity with age may be responsible for the changes in silicon levels in senescence.
Silicon, considered heretofore as an environmental contaminant, is one of the most recent trace elements established as “essential” for higher animals and a mechanism and site of action have been identified. Silicon has been demonstrated to perform an important role in connective tissue, especially in bone and cartilage. Abnormalities of both bone and cartilage have been produced in silicon-deficient animals. These skeletal abnormalities were associated with a reduction in matrix components, resulting in the establishment of a requirement for silicon in collagen and glycosaminoglycans formation. Silicon’s primary effect in bone and cartilage appears to be on the matrix, formation of the organic matrix appearing to be more severely affected by silicon deficiency than the mineralization process. Additional support for silicon’s metabolic role in connective tissue is provided by the finding that silicon is a major ion of osteogenic cells, especially high in the metabolically active state of the cell, and furthermore, that silicon reaches high levels in mitochondria of these cells, indicating that silicon participates in the biochemistry of the subcellular, enzyme-containing structures. Although it is clear from the body of recent work that silicon performs a specific metabolic function, a structural role has also been proposed for silicon in connective tissue. A relationship established between silicon and aging is probably related to glycosaminoglycan changes.
The subject of silicon toxicity is almost invariably associated with the silicosis problem. As with many other essential elements, certain chemical forms of silicon may be toxic if inhaled or ingested in large amounts although the chronic oral ingestion of small amounts of many siliceous materials is generally considered safe as evidenced by the number of silicates on the FDA GRAS list. However, the potential for nephrotoxicity of long-term consumption of certain silicon compounds should not be overlooked.
Also a summary from E. M Carlisle
The antiatheromatous (anti-arteriosclerosis) action of silicon that we have demonstrated has been observed by other authors, Gendre and Fourtillan et al. in particular.
Does silicon modify the quantity of lipids found in the serum and in the aortic wall? A lower cholesterol concentration in the serum of silicon-fed rabbits as compared to rabbits receiving only cholesterol is insufficient to explain the antiatheromatous action observed. On the other hand, ultracentrifugation of the serum of rabbits receiving silicon and those that did not showed no significant difference in the distribution of cholesterol and triglycerides in lipoprotein fractions, except for a transfer of HDL cholesterol on VLDL among silicon-fed rabbits as compared to the others.
Yet some authors noted that the increase in oleic acid found in the plasma and the arterial wall during experimentally-induced atheromas was inhibited by silicon.
The most important effect silicon has is to reduce permeability of the arterial wall; it heightens the impermeability of conjunctive tissue and intracellular cement, as shown by Holt and Osborne.
We verified this theory by measuring the diffusion of a dyed substance in rabbit derma and found that the addition of silicon inhibits such diffusion. Moreover, the thickening of elastic fibers and particularly of the internal elastic lamina, which normally already constitutes a lipid barrier, may explain why penetration of large lipidic inclusions is less deep.
It should be noted, however, that lipid concentration in the aortas of rabbits receiving an atherogenous diet plus silicon is higher than the concentration in normal arteries.
Alterations in elastic fibers are known to be parallel to the degree of lipid infiltration, often even preceding it. Moreover, lipid deposits are most important in areas in which metachromatism is the most intense, the latter being related to an increase in sulphate groups of glycosaminoglycans. It has also been proven that beta-lipo proteins and particularly VLDL can form compounds with glycosaminoglycans. All these facts suggest that damaged arteries fix lipids more often in the form of confluent masses or plaques than healthy arteries.
Silicon maintains the integrity of elastic fibers and of ground substance and lowers the frequency of atheromatous plaques.