Silicon

Physiological Role
Insufficient data are available to establish a Si requirement
Sources of Si
Deficiency Signs
Toxicity

I.  Physiological Role

1. Si is required for bone matrix formation and early stage of bone calcification
   1. Both cartilage and bone appear to be dependent on Si for formation .of collagen and mucopolysaccharide
      1. Si is a bound component of glycosaminoglycans
      2. As a cross linking agent it contributes to stability of connective tissue components
   2. Si may take part in the sequence of events leading to calcification of bone
      1. Dietary Si increases rate of bone mineralization
      2. The effect is particularly apparent under low Ca intake
      3. Mechanism of action in bone appears somewhat similar to that of vitamin D, but is independent of the action of vitamin D
      4. There is a relationship between Si, Mg and F in growing bone
   3. In bone, Si is uniquely localized in active growth areas where a relationship with Ca is established
      1. Si is concentrated in the cytoplasm of the active bone-forming cell, the osteoclast, in the mitochondria
      2. When total Si, Ca, P and Mg stores of single osteogenic cells were successfully measured, Si was shown to be the major anion

II.  Insufficient data are available to establish a Si requirement.

An estimated daily dietary (EDDI) of 20-50 mg is suggested for humans (J Nutr. 136-2452S, 1966)

III.  Sources of Si

1. Si of plants is present mainly as silica (silica gel), soluble silicates, and partly in organic combination, bound to the cellulosic structure of the cell
2. Cereal grains high in fiber are richer in Si than low fiber grains. Rice hulls are very high in Si

IV.  Deficiency Signs

1. Bone abnormalities
   1. Skull short and deformed
   2. Long bones reduced in circumference, with thinner cortex, less flexible
   3. More primitive nodular pattern of bone arrangement lacking in normal trabecular pattern
   4. Decreased collagen and glycosaminoglycans in bone and connective tissue
2. In chick, pale legs and comb, anemic skin and mucous membranes, no wattles and comb severely attenuated

V.  Toxicity

1. Silicosis is a chronic lung disease caused by inhalation of Si bearing dust
2. Peanut hay colic in horses and mules in Coastal Plain
3. Depressed digestibility of forages (J. Anim. Sci. 33:466, 1971; 34:839, 1972; 41:882, 891, 1975)
4. Formation of kidney stones in ruminants (J. Anim. Sci. 41:891, 1975; 61:219, 61:219, 1981; 68:498, 1990. Can. J. Anim. Sci. 53:55, 1973; Am. J. Vet. Res. 28:1743, 1967)
5. Excessive tooth wear

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