More food for thought... consider this generic statement I mentioned previously that I believe many here subscribe to...
"I believe vaping is less harmful than cigs but it can't be healthy"
Consider the facts:
1. In small doses, (a synthetically produced form of) nicotine, known as Niacin (aka Nicotinic Acid) is a popular vitamin supplement with known health benefits. The FDA recommended amounts of Niacin taken in supplements appear to be similar to the amounts of nicotine many of us vape (up to 35mg/day per the Mayo Clinic). Look it up.
2. Nicotine, in "heavy doses" that we vape, is known to aid in the alleviation of various neurological symptoms, and without any known significant side effects, unlike most drugs used to treat those diseases now. And in fact much of what we know as facts about nicotine dependency is a byproduct of those studies.
3. PG is known to be antibacterial and antiviral. There is at least one study, that has been linked here on this site, suggesting that inhaling PG helps to prevent colds and flu.
It is possible, and this is pure speculation, that PG could also help to mitigate other ailments. For example, I believe there is some thought that lung cancer may be caused by a virus. It is not beyond the realm of possibility that PG might just help kill that very nasty virus, assuming it even exists and is the proximate cause for that terrible disease. Just to say that blind speculation can cut both ways. There may be other ailments associated with our respiratory system that would benefit from regular inhalation of PG
4. It is a FACT that any significant possible harm caused by vaping is pure speculation, based on the idea of we can't prove that negative. None of it is proved, verses the clear peer reviewed evidence of the above.
So... it seems to me, objectively reviewing the FACTS we know, that it is far more likely that vaping is healthy and promotes good health than it is likely that it is harmful. May I daresay it is fact? And worse case it may be a bit of both, with a net benefit or detriment to be decided in some distant future when facts are more important than propaganda.