Synthetic amorphous silica (SAS) can enter the body through breathing or with food. However, the body excretes natural silica and also SAS completely and unchanged.
Dust particles containing silica are caught in the nose when you breathe and are discharged with nasal secretions. Two mechanisms prevent smaller particles from entering the bloodstream. On the one hand, the particles are transported out by mucus and cilia, and on the other hand, the phagocytes continuously clean particles from the lung tissue. Only a very small, negligible part actually gets into the bloodstream, but this is then discharged via the kidneys.
SAS with the classification E 551 is added to food. When this food is eaten, a small part of the silica can be dissolved and get into the bloodstream – this is discharged via the kidneys. The body excretes the remainder normally.
No SAS enrichment in the body has been discovered with any of the ingestion paths.
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Most SAS consumed with food is excreted in the stool. Only a very small part is reabsorbed into the bloodstream via the gut in the form of soluble silica and is then discharged quickly again with urine. If silica (in the form of E 551) is added to food, in an aqueous environment and depending on the pH, soluble silica can form which can be reabsorbed by the body (SiO2 + 2H2O → H4SiO4; orthosilicic acid also known as soluble silica).
In the mouthy cavity and stomach this is not a relevant mechanism for the absorption of silica, even if E 551 is “freely” available after its carrier substance (e.g. salt) has dissolved. The mucous layer in the mouth cavity, which is much thicker (70-100 µm) than the silica particles, creates an effective barrier and protects the oral epithelium; consequently, appreciable resorption via the mouth cavity is practically impossible. Even with a very acidic pH, as found in the stomach, E 551 is not decomposed; soluble silica can only be released and reabsorbed in the small intestine. This small amount is integrated into the body silicon pool.
It is likely that silicon plays a structural role in the formation of connective tissue, including bones and skin. The highest silicon concentrations are found in bones and connective tissue and are higher in a growing organism than in old age. The silicon level in blood is kept constant by resorption and excretion. No enrichment of SAS in the body has been discovered, regardless of how it enters the body.