General Description
Silica (silicon dioxide), a nonmetallic crystalline mineral composed
of silicon and oxygen, is the most abundant mineral in the earth's
crust, where it is most commonly found in the form of quartz or
sand. Only recently recognized as having a role in human nutrition,
silica's functions in the body are not well understood. It appears
to play a role in the mineralization of bones and teeth,1,2
and in the formation of collagen,3,4 the primary
protein component of bones, connective tissues, hair, skin, and
nails. Supplemental forms of silica include colloidal silicic acid,
sodium metasilicate, and the silica-rich herb horsetail grass. Silica
is also available in a homeopathic form known as silicea.
Food sources
Good sources of silica include whole grains, green leafy vegetables,
root vegetables, asparagus, and sunflower seeds.
Health applications
Deficiency symptoms
There are no known cases of silica deficiency in humans. The body
uses silica only in minute amounts, which most people receive in
their regular diets. In animal studies, silica deficiency caused
abnormalities in bone and connective tissue formation.5
Cardiovascular
health
Preliminary studies indicate that silica may have a protective
effect against cardiovascular disease. In laboratory rabbits placed
on a high-cholesterol diet, the addition of silica to the diet
minimized the lipid imbalances associated with atherosclerosis.6,7
To date, no studies have been conducted to examine the effects
of silica on the development of atherosclerosis in humans.
Mental function
Some studies suggest that silica may help protect against cognitive
impairment associated with accumulations of aluminum in the brain.
In one study, researchers observed that high aluminum levels had
a negative impact on mental function when silica levels were low,
but there was a protective effect when silica levels were high.8
Other studies indicate that some forms of silica can reduce the
body's absorption of aluminum in the digestive tract.9
While these studies are encouraging, further research is needed
before scientists can determine whether silica may play a role
in the prevention of Alzheimer's disease and other forms of mental
impairment associated with high aluminum levels.
Dosage/toxicity
There is no established RDI for silica. The average diet is estimated
to provide 5 to 20 mg of silica per day, and this appears to be
sufficient for most people. No toxicity has been associated with
high silica intake. Inhalation of large amounts of silica (as
occurs in people with high levels of industrial exposure) can
cause a respiratory disease known as silicosis, and is associated
with an increased risk for lung cancer.10
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