The same goes for nicotine.
If most vapers are like me, and it seems I am not alone here, is that you end up with some collection. You don't vape 1 liquid all day, at least not every day, that's just part of the art in vaping. Not forgetting to mention, I can't see how they are capable of adding enough volume of any one vitamin to the liquid itself, to the point where someone is absorbing too much of it. I don't think it's possible with the current PG/VG bases. Maybe it's possible for a small mammal that vapes, like a lab rat, but a full grown adult?