Silicon (Si) is present in biologic material as a silanate, an ether
(or ester-like) derivative of silicic acid which may play a role in the
structure of glycosaminoglycans and their protein complexes. Connective
tissues including aorta, trachea, tendon, bone, and skin and its
appendages contain much of the silicon that is retained in the body.
Deficiencies: Most of the signs of silicon deficiency
in chickens and rats indicate aberrant metabolism of connective tissue and
bone. Chicks fed a semi-synthetic, silicon-deficient diet exhibited skull
structure abnormalities associated with depressed collagen content in bone
and long bone abnormalities characterized by small, poorly formed joints
and defective endochondral bone growth.
Diet recommendations: As no appropriate human data are
available, extrapolation from limited animal data suggest that the human
requirement for silicon is quite small, in the range of 2 to 5 mg/day.
However, silicon found in most diets as aluminosilicate and silica is not
absorbable or as available as sodium metasilicate. Additionally, factors
such as aging and low estrogen status apparently decrease the ability to
absorb silicon. Thus, the recommended intake of silicon may be found to be
between 5 and 10 mg/day.
Food sources: Dietary silicon intake of humans varies
greatly with the amount and proportions of foods of animal (silicon-low)
and plant (silicon-high) origin consumed and the amounts of refined and
processed foods in the diet. Normally, refining reduces the silicon
content of foods. However, silicate additives have been increasingly used
in prepared foods and confections as anti-caking or anti-foaming agents.
Although this increases total dietary silicon, most of it is not
bioavailable. The silicon content of drinking water, and beverages made
thereof, shows geographical variation; silicon is high in hard water and
low in soft water areas. The richest sources of silicon are unrefined
grains of high fiber content and cereal products. The daily average
intakes of silicon apparently ranges from about 20 to 50 mg/day.
Toxicity: Most silicon compounds are essentially
nontoxic when taken orally. Magnesium trisilicate, an over-the-counter
antacid, has been used by humans for more than 40 years without obvious
deleterious effects. Ruminants consuming plants with a high silicon
content may develop siliceous renal calculi; renal calculi in humans may
also contain silicates.
Recent research: In rats, bone hydroxyproline is
decreased, plasma amino acid and bone mineral composition is altered, and
femur alkaline and acid phosphatase are decreased by silicon deprivation.
However, growth of rats is not markedly affected by silicon deprivation.
