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Trace Elements in Abiotic and Biotic Environments
High Si levels are present in the bone, kidney, tendons, and walls of the aorta,
with the nails containing its highest levels (up to 1500 mg/kg). Lower levels of silicic
acid are present in red blood cells or serum, approximately 44 mg/kg in red cells and
20 mg/kg and in plasma. It is also accumulated in the liver, spleen, and lung, as well
as in breast milk. It interacts with a number of elements, including Cu, Zn, and Ge.
It promotes the Ca absorption and metabolism. Silicon may significantly reduce the
absorption of Al, and thus reduce the risk of developing Al-induced Alzheimer’s disease (Edwardson et al. 1993). Water-soluble forms of Si are absorbed in the intestinal
tract, with excess amounts eliminated by the kidneys within 4–8 hours following
ingestion (Jugdaohsingh 2007). Thus, it is unlikely for Si to accumulate in excessive
amounts in healthy individuals. Patients on dialysis may accumulate Si because renal
failure prevents the excretion of Si.
Silicon is an essential mineral for the bone formation. It improves bone matrix
quality and facilitates bone mineralization. Increased intake of bioavailable Si is
associated with increased bone mineral density. Its supplementation in humans and
animals increases bone mineral density, and improves bone strength (Price et  al.
2013). All tissues contain large amounts of Si, when they are perfectly healthy, but its
amount decreases with age (approximately 0.1 mg/yr), and then the tissues undergo
gradual degradation (Jugdaohsingh 2007). Depleted levels of Si are also in some
pathological states, such as atherosclerosis or neoplastic diseases.
Silicon is nontoxic as an element and in all its natural forms, mainly silica and
silicates, which are the most abundant elements, but some of its species may cause
major damage to the lungs. Long-term exposure to silicates such as asbestos is a
severe health problem. Diatoms and some protozoa, sponges, and plants use silicon
dioxide (SiO 2 ) as a structural material.
Silicon is an important essential trace element in human nutrition. The recommended daily intake is about 10–25 mg (Powell et al. 2005). Its deficiency is mostly
associated with losses of connective tissue components, such as glycosaminoglycanes, collagen, and elastin. The most readily absorbable form of silicon is orthosilicic acid (H 4 SiO 4 ) (Sripanyakorn et al. 2005).
The role of Si in human biology is poorly understood, although its beneficial influences are observed in some diseases, such as osteoporosis, atherosclerosis, progress
of diabetes, propagation of neoplastic process, and occurrence of heart diseases.
Silicon was also found to reduce negative effects of some processes such as skin,
hair, and nail aging (Jugdaohsingh 2007).
The bioavailability of Si for intestinal absorption depends on the solubility of its
compounds. Foods derived from plants rather than from animals provide the highest
sources of dietary Si. Unrefined cereals and grains have high Si content, especially
oats and oat bran. The principal sources of dietary Si are whole grains, fruits, beverages, and vegetables (Table 43.2). In particular, high levels of bioavailable Si are in
beer, which is made from barley malt (Cejnar et al. 2013).
Silicon is also available as a food supplement in tablet and solution form for bone
and connective tissue health, although there are no formal data on its in vivo utilization or safety following sustained dosing (Jugdaohsingh et al. 2013).