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489
J. Elem. s. 489–497 DOI: 10.5601/jelem.2011.16.3.13
prof. zw. dr hab. Kazimierz Pasternak, Chair and Department of Medical Chemistry, Medi-
cal University of Lublin, ChodŸki 4a, 20-093 Lublin, Poland, phone: +48 81 535 73 61,
e-mail: kazimierz.pasternak@umlub.pl
REVIEW PAPER
SILICON IN MEDICINE AND THERAPY
Anna Boguszewska-Czubara, Kazimierz Pasternak
Chair and Department of Medical Chemistry
Medical University of Lublin
Abstract
Trace elements are a very important factor affecting functions of living organisms.
Silicon, the third most abundant trace element in the human body, is present in all heal-
thy tissues of people. It is especially strongly associated with connective tissues, as it has
been found to participate in bone development, collagen formation and mineralization of bo-
ne matrix. Silicon has also been suggested to be involved in mammalian hormonal control
and to protect people from heart diseases.
An average dietary intake of silicon is about 20-30 mg/person/day, with higher intakes
for men than women. Silicic acid or orthosilicic acid are the bioavailable forms of silicon,
found mainly in food rich in fibre and whole grains, in vegetables, fruit and in drinking
water. Various alcoholic beverages such as beer or wine also contain considerable amounts
of silicon. Silicon provided with food is digested in the gastrointestinal tract to silicic acid,
which is then absorbed. With blood, it is distributed into various tissues and organs, where
it can exerts its action. The highest amounts of silicon are accumulated in the kidneys,
liver, bone, skin, spleen, lungs, while free orthosilicic acid, not bounded to proteins, occurs
in blood. The amount of silicon in tissues decreases with age. Depleted levels of silicon
have also been observed in some pathological states e.g. atherosclerosis.
The aim of the paper has been to present the role of dietary silicon in living organi-
sms. Silicon is necessary for the growth and bone calcification and as a biological cross-
linking agent of connective-tissue-based membrane structures. This element is considered
to have beneficial effects on several human disorders, including osteoporosis, ageing of
skin, hair and nails or atherosclerosis. It has also been suggested that silicon and silicic
acid may decrease the bioavailability of aluminium by blocking the uptake of the latter by
the gastrointestinal tract and impeding its reabsorption in the kidneys, thus protecting an
organism against the toxic (especially neurotoxic) action of aluminium. Anticancer, antia-
therosclerotic and antidiabetic effects of silicon have also been suggested.
Key words: silicon, silicon metabolism, bone, connective tissue, aluminium toxicity.
490
KRZEM W MEDYCYNIE I LECZNICTWIE
Abstrakt
Pierwiastki œladowe s¹ bardzo wa¿nym czynnikiem warunkuj¹cym prawid³owe funk-
cjonowanie organizmów ¿ywych. Krzem, trzeci pierwiastek œladowy pod wzglêdem rozpo-
wszechnienia w organizmie cz³owieka, jest obecny we wszystkich zdrowych tkankach.
Szczególn¹ rolê odgrywa krzem w tworzeniu i funkcjonowaniu tkanki ³¹cznej, poniewa¿
bierze on udzia³ w rozwoju koœci, tworzeniu kolagenu i mineralizacji macierzy kostnej.
Krzem uczestniczy równie¿ w kontroli hormonalnej u ssaków oraz w ochronie przed cho-
robami serca u ludzi.
Dzienna dawka krzemu dla doros³ego cz³owieka powinna wynosiæ 20-30 mg, przy czym
zapotrzebowanie na krzem jest wiêksze u mê¿czyzn ni¿ u kobiet. Przyswajaln¹ form¹ krze-
mu jest kwas krzemowy lub kwas ortokrzemowy, którego Ÿród³em w diecie s¹ zbo¿a, wa-
rzywa, owoce oraz woda pitna. Krzemiany z po¿ywienia s¹ w przewodzie pokarmowym hy-
drolizowane do ³atwo przyswajalnego kwasu ortokrzemowego, który wraz z krwi¹ jest
rozprowadzany do wszystkich tkanek i organów. Najbogatsze w krzem s¹ nerki, w¹troba,
koœci, skóra, œledziona oraz p³uca, a we krwi krzem wystêpuje w postaci wolnego kwasu
ortokrzemowego, niezwi¹zanego z bia³kami. Wszystkie tkanki zawieraj¹ du¿o krzemu, gdy
s¹ ca³kowicie zdrowe, natomiast jego poziom zmniejsza siê w nich wraz z wiekiem cz³owie-
ka i tkanki ulegaj¹ wówczas stopniowej degeneracji. Zani¿ony poziom krzemu obserwuje
siê równie¿ w pewnych stanach chorobowych, na przyk³ad w mia¿d¿ycy.
Celem pracy by³a prezentacja zale¿noœci miêdzy krzemem przyswajanym z po¿ywienia
a wp³ywem, jaki wywiera on na organizmy ¿ywe. Krzem jest niezbêdny w procesie wzro-
stu oraz wapnienia i mineralizacji koœci, jest równie¿ czynnikiem sieciuj¹cym struktury
tkanki ³¹cznej. Pierwiastek ten wywiera korzystny wp³yw w pewnych schorzeniach, takich
jak osteoporoza, starzenie siê skóry, w³osów i paznokci, mia¿d¿yca. Krzem ma unikatowe
w³aœciwoœci wi¹zania metali ciê¿kich w nierozpuszczalne kompleksy, ograniczaj¹c ich szko-
dliwe dzia³anie. Dodatkowo, kwas krzemowy hamuje wch³anianie glinu i jest antidotum na
jego toksyczne dzia³anie. Sugeruje siê równie¿ jego dzia³anie przeciwcukrzycowe, przeciw-
mia¿d¿ycowe oraz przeciwnowotworowe.
S³owa kluczowe: krzem, metabolizm krzemu, koœci, tkanka ³¹czna, toksycznoœæ glinu.
INTRODUCTION
Trace elements are a very important factor, affecting functions of living
organisms. Although silicon is the second most abundant element in bio-
sphere after oxygen, due to its very poor bioavailability to the human or-
ganism, its influence on metabolic processes is only fragmentarily known
and poorly understood (BIRCHALL et al. 1996).
The daily recommended intake (DRI) has not been determined yet, al-
though a suggested daily dose of silicon should reach 20-30 mg for an adult,
which corresponds to 0.28-0.43 mg kg–1 b.w. a day for a man weighing 70kg.
Dietary sources of silicon are grains (rice, barley, oat, wheat) and grain
products (breakfast cereals, bread, pasta), root vegetables (carrots, beetroot,
radish, onion, potatoes), bean, corn, fruit (especially bananas) as well as
dried fruit (raisins) and nuts. Silicon is highly available from drinking water
491
and its concentration depends upon the geology of water intake surround-
ings because Si is derived from weathering rocks and soil minerals (JUGDA-
OHSINGH et al. 2002, SRIPANYAKORN et al. 2005). Beer and wine are also rich
sources of dietary silicon, containing quite high amounts of orthosilicic acid,
a Si bioavailable form (THIEL et al. 2004, GONZÁLEZ-MUÑOZ et al. 2008). Drink-
ing infusions of silicon containing herbs (like Common Horsetail, Knotweed,
Red Hemp-nettle, Lungwort) can supplement dietary deficits of that element
as well as to alleviate symptoms of some diseases (ZIELECKA 1996).
Silicates from food are hydrolyzed into readily available orthosilicic acid
in the gastrointestinal tract (BAREL et al. 2005). The exact site where silicic
acid is absorbed from the gastrointestinal canal has not been established,
although it has been suggested that silicon compounds from food in the
presence of hydrochloric acid and other gastric acids in the stomach are
broken down into orthosilicic acid, which easily diffuses through mucous
membranes into the blood circulation system. In the Framingham and Fram-
ingham Offspring studies, values of an average daily silicon availability have
been determined as 12.1-13.5 mg for men and 9.9-10.2 mg for women (JUGD-
AOHSINGH et al. 2002, JUGDAOHSINGH et al. 2004). The peak increase in the
serum silicon concentration was observed 60-84 minutes after orthosilicic
acid consumption (REFFITT et al. 1999) and 100-120 minutes after ingestion of
a silicon-rich meal (13.15 mg) (JUGDAOHSINGH et al. 2002). Kidneys play a key
role in silicon turnover. Silicon is readily filtered by the renal glomerulus
because it does not form any bonds with plasma proteins (SRIPANYAKORN et al.
2005). Hence, about 70-80% of plasma silicon is eliminated by kidneys with-
in 3-8 hours after meal ingestion (POPPLEWELL et al. 1998). Thus, urinary Si
excretion is a good surrogate marker of silicon absorption (WIDNER et al.
1998, REFFITT et al. 1999). Silicon in the form of inorganic silicate occurs in
large quantities in kidneys and is a constant component of urine. Silica also
fulfils a role of protective colloid preventing appearance of urinary stones,
although silicon excess may lead to formation of renal deposits and calculus
(ZIELECKA 1996). Studies on kinetics of silicon absorption and elimination dem-
onstrated that the organs and tissues characterized by the highest concen-
trations of silicon are connective tissues, bone, skin liver, heart, muscle,
kidneys and lungs (POPPLEWELL et al. 1998, JUGDAOHSINGH 2007). The amount
of silicon in tissues decreases with age, probably because the organ respon-
sible for silicon absorption and turnover in an organism is the thymus, which
undergoes atrophy with age.
492
INFLUENCE OF SILICON ON THE DEVELOPMENT
AND FUNCTIONS OF A LIVING ORGANISM
For a long time, silicon has been thought to be an inactive substance,
not participating in biochemical processes due to its overall unavailability to
living organisms. Only recently it has been recognized as one of the most
essential trace elements in human metabolism.
The highest concentrations of silicon have been found in organs consist-
ing of connective tissues such as the aorta, trachea, bones and skin. The
content of silicon in human skin is 49.5 µg g–1 of tissue, in hair 42.0 µg g–1
of tissue and in nails 26.12 µg g–1 of tissue. A high content of silicon in the
connective tissue is attributed to its presence in protein complexes, which
form the structure of the tissue as a cross-linking entity (ZIELECKA 1996). In
animal studies, the aorta, trachea and tendons were found 4 or 5-fold richer
in silicon than the liver, heart and muscles. In blood, silicon occurs in the
form of free orthosilicic acid, not bounded with proteins, reaching a concen-
tration from 50 to 200 µg L–1, depending on its content in a diet (D’HAESE et
al. 1995). The overall silicon content in a man weighing 70 kg is from 140
to 700 mg, which classifies that element as the third most abundant mac-
roelement, after zinc and iron (SRIPANYAKORN et al. 2005). All tissues contain
large amounts of silicon when they are perfectly healthy, but its amount
decreases with age and then the tissues undergo gradual degradation. De-
pleted levels of silicon have also been observed in some pathological states
like atherosclerosis or neoplastic diseases (BISSÉ et al. 2005).
In vitro studies showed that orthosilicic acid in a physiological concen-
tration stimulates collagen synthesis and, through an increase in prolylhy-
droxylase activity in human osteoblasts, it stimulates their differentiation
(REFFITT et al. 2003, JUGDAOHSINGH et al. 2004). Much silicon has also been
found in human osteoblasts, highly metabolically active cells. In the human
organism, silicon is mainly accumulated in sites of active bone growth. Nu-
merous studies have confirmed that silicon actively participates in the proc-
ess of bone calcification and accelerates the rate of bone mineralization. Sili-
con deficiency causes deformations or delay in bones formation as well as
disorders in joint cartilage and connective tissue formation (RICO et al. 2000).
There is evidence that dietary silicon is able to lower the plasma total,
VLDL and LDL cholesterol level (WACHTER et al. 1998) and to significantly
inhibit the atherosclerotic process induced by a cholesterol rich diet (PELUSO,
SCHNEEMAN 1994). According to some authors, silicon exerts antiatherosclerot-
ic action mainly through increasing membrane permeability and the basal
substance of arteries. Studies carried out on animals proved that silicon
administered in the form of silica prevented occurrence of endoxan or strep-
tozotocin-induced diabetes (OSCHILEWSKI et al. 1986). Antineoplastic properties
of silicon, which can be associated with its influence on the connective tis-
493
sue synthesis, thereby reducing progress and propagation cancer, have been
reported. Synthetic silicon compounds, e.g. silitrans derivatives, applied to-
gether with cytostatics, improved manifold the effectiveness of the latter
(JANCZARSKI, JANCZARSKI 1991). Silicon also plays a role in immune functions
influencing lymphocytes proliferation (SEABORN et al. 2002).
Silicon has a unique property of binding heavy metals into insoluble
complexes, thereby limiting their possible harmful effects. Additionally, sil-
icic acid inhibits the gastrointestinal absorption of aluminium, a metal
of neurodegenerative action, whose role in the pathogenesis of Alzheimer’s
disease is stated to be significant. Silicon is reported to be an antidote to
aluminium toxicity as it reduces Al bioavailability (BELLIA et al. 1996, REFFITT
et al. 1999, DOMINGO 2006).
Silicon metabolism is connected with the turnover of numerous macro-
and microelements. With calcium, silicon is involved in the processes of bone
decalcification as well as calcification. Silicon is calcium-antagonist, there-
fore it can regulate calcium and magnesium turnover. It acts synergistically
with copper, thus depressing the zinc concentration in tissues. It also antag-
onises harmful effects of aluminium on osteogenesis. Additionally, silicon
influences the metabolism of such elements as P, Cl, Na, K, S, Mo, Co
(O’CONNOR et al. 2008). This element is required to remove harmful and toxic
heavy metals from the brain (BIRCHALL et al. 1996, PERRY, KEELING-TUCKER 1998,
BOGUSZEWSKA et al. 2003).
Disturbances in silicon turnover have been reported in patients suffer-
ing from different skin problems or tuberculosis and in persons treated with
antibiotics and chemotherapeutics for a long time (O¯AROWSKI 1996, CALOMME,
VANDEN BERGHE 1997).
SILICON AND BONE
In the 1980s, the earliest studies on silicon biochemistry, carried out by
Carlise, suggested strong connection between a proper level of dietary sili-
con intake and normal growth of animals (chickens and rats) (CARLISLE 1980).
Particularly collagenous tissues, like bones, cartilages, skin and hair were
markedly abnormal in Si-deprived animals. Bone health subsequently became
the main subjects for researchers studying the biological role of silicon, main-
ly because osteoporosis, characterized by low bone mass, is a growing health
problem worldwide and leads to marked disability, increased mortality and
raised health care costs (SRIPANYAKORN et al. 2005, JUGDAOHSINGH 2007).
According to recent studies, silicon is co-located with calcium in the
osteoid tissue, thus some interactions between these elements were sus-
pected to occur in processes of bone growth and mineralization (PERRY, KEEL-
ING-TUCKER 1998). In the earliest stage of calcification, in active calcification
494
sites in young bones, there is a direct relationship between silicon and calci-
um when the calcium content of the preosseous tissue is very low. There-
fore, it has been suggested that silicon is associated with calcium in the
early stage of bone formation. It was demonstrated that dietary silicon in-
creased the rate of mineralization, especially in calcium-deficient rats (KIM
et al. 2009). Evidence has been obtained to indicate that when rats are fed
low calcium diets, bone composition is affected by silicon deprivation: the
deprivation depressed concentrations of calcium, magnesium, and phospho-
rus in the tibia and skull (CARLISLE 1980). Additionally, silicon was found to
promote the union of a bone after a fracture, in contrast to calcium, which
can actually slow down the healing process or interfere with it altogether,
especially when calcium levels are very high. All these facts can be inter-
preted as promoting bone mineralization by silicon under the conditions of
a low level of calcium in a diet, but on the other hand in may also indicate
interactions between calcium and silicon in the gut lumen, which can re-
duce the gastrointestinal absorption of silicon (SRIPANYAKORN et al. 2005, JUGD-
AOHSINGH 2007).
SILICON AND SKIN, HAIR AND NAILS
Many studies on silicon influence on bone and cartilage formation con-
firmed, that the element’s primary effect is thought to be on matrix synthe-
sis rather than mineralization (CALOMME, VANDEN BERGHE 1997). Silicon in form
of orthosilicic acid at physiological concentrations was found to stimulate
collagen type 1 synthesis in human osteoblast-like cells and skin fibroblasts.
Silicon treatment also enhanced osteoblastic differentiation. The suggested
mechanism of orthosilicic acid is to modulate activity of prolyl hydroxylase,
an enzyme involved in conversion of hydroxylate proline to hydroxyproline
in the process of collagen formation, rather than alteration in collagen type
1 gene expression (REFFITT et al. 2003). Silicon was also reported to be nec-
essary in formation of glycosaminoglycans in bone and cartilage due to its
structural role in the cross-linking of glycoaminoglycans in connective tis-
sue. As type 1 collagen and its monomer hydroxyproline are major constitu-
ents of skin, the improvement in skin parameters, like hydratation or mi-
crorelief (roughness), after silicon supplementation indicates on potential
regeneration or de novo synthesis of collagen fibers. Treatment with silicon
also might improve the glycosaminoglycan structure in the dermis and the
keratin structure in hair and nails, what was seen through decrease in hair
and nails brittleness (BAREL et al. 2005).
495
SILICON AND ALUMINIUM TOXICITY
Despite the widespread occurrence of aluminium in the environment as
well as its presence in trace amounts in almost all plants and animals, for
a long time Al has been considered to be indifferent to living organisms.
However, aluminium can have deleterious effects on plants, animals as well
as on human beings. In the terrestrial environment, that is in plants, it is
responsible for the development of a stunted and brittle root system;
in animals and human it causes growth disorders and disturbed neurological
functioning (Alzheimer type senile dementia, amyotrophic lateral sclerosis,
a type of Parkinson’s disease) (DOMINGO 2006). Aluminium is even more toxic
in the aquatic environment, where it can be fatal to fish. Acute aluminium
toxicity can be associated to its ability to bind to biologically important lig-
ands, like phosphate groups in membranes, DNA and ATP. Aluminium is
also able to bind to aionic sites on fish gill epithelia, stimulating excessive
mucus production, which causes potentially lethal disturbances in respira-
tion as well as ion transport (PERRY, KEELING-TUCKER 1998). The idea that
silicon may be involved in a mechanism to protect against aluminium poi-
soning, inspired by Si-Al interactions observed in inorganic chemistry, has
been checked in numerous experiments. The most recent research shows
that silicic acid interacts with metal ions that are basic at physiological pH,
such as aluminium. Silicon is involved in relieving Al toxicity in many dif-
ferent biological systems as well as in reducing aluminium bioavailability in
humans by reducing its gastrointestinal absorption and enhancing its renal
excretion (BIRCHALL et al. 1996, REFFITT et al. 1999). Orthosilicic acid from
beer was found to increase the urinary output of aluminium, perhaps by
interacting with filterable Al in renal tubules, forming hydroxyaluminosili-
cates and thus preventing re-absorption of aluminium (BELLIA et al. 1996).
These findings may benefit transplant patients in clearing the accumulated
aluminium as well as other patients, protecting them from harmful effects
of aluminium excess.
The role of silicon in human biology is poorly understood, although the
above findings and studies may suggest beneficial influence of silicon on the
human organism in some diseases, like osteoporosis, atherosclerosis,
progress of diabetes, propagation of neoplastic process as well as occurrence
of heart diseases (TURNER et al. 2008). Silicon was also found to reduce nega-
tive effects of some processes as skin, hair and nails ageing (JUGDAOHSINGH et
al. 2002). It is very important for regenerating tissues, activating vital proc-
esses of cells and improving the general immunity of organism. Therefore,
further studies on silicon biology, biochemistry as well as silicon homeosta-
sis and its interactions with essential mineral elements as well as with oth-
er biologically important molecules are necessary.
496
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