In which everyday products quartz (silicon dioxide) might be found?

Is the silicon dioxide used in vitamins/supplements in the nanoparticle form? Is it dangerous?

• Most multivitamin or combination supplement products I've come across use silicon dioxide (or silica, SiO2) as an excipient. Recent research has shown that silicon dioxide nanoparticles (size 1-1000nm) can be cytotoxic (i.e. kill mammalian cells) but I'm not sure as to whether "larger" silica particles have this property. What is unclear to me is whether the silicon dioxide used as excipients in nutritional supplement products are formulated in larger pieces (which would not be expected to be absorbed by the GI tract) or if they are indeed being added as nanoparticles instead (which could potentially be much more harmful). While nanoparticles are a very recent and emerging field and much of the research is preliminary, because of their higher surface area, it has been suggested that they can be more reactive, catalytic, or harmful to mammalian cells than "larger" particles (of the same molecular formula).

• Answer:

  It would not be used if it was