I enjoy reading the studies, I learn a lot from the actual data rather than the erroneous claims. The truth about aldehyde formation in vaping is quite interesting. One study showed that aldehydes are formed by VG at temperatures lower than with PG.. The question is how hot our juice actually gets at a given coil temperature - a saturated wick doesn't suddenly go to 400 deg when the coil does, but likely the juice just beneath the coil reaches that temperature. I suggest reading for yourself, In my opinion, the truth is somewhere between "aldehydes are higher vaping than smoking" claims and the "nothing is there, the studies are false" claims
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5377270/
"In this study, the amounts of formaldehyde, acetaldehyde, and acrolein from GL were 21.10±3.80, 2.40±0.99, and 0.80±0.50 μg/mg-GL at 318°C, respectively. It is noteworthy that the level of formaldehyde was about ten times higher from GL than from PG at the same temperature. Furthermore, the evolution of formaldehyde and acetaldehyde began at relatively lower temperatures (108 and 215°C, respectively), while the development of acrolein began at a relatively higher temperature (~270°C) (
Fig 3b). "
And this study also indicates that the formation of aldehydes and Acrolein can come from VG ("GL" below), and aldehydes from PG alone, with no flavorings. Keep in mind the study below heated the liquids to those temperatures, therefore the results are not indicative of the carbonyls generated from a vaping device with the COIL at those temperatures (indeed, other studies have shown low amounts for modern devices at normal power levels):
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0169811
So, somethings there. How much? Likely not much at low power levels, moderate temperatures. But if you're vaping high VG at high power, high coil temperatures, there's little doubt in my mind your getting some amount of aldehydes, though I would suspect far less than smoking (if you've vaping at 600F you might be close, lol).