1) Having a science background w/statistics/math as well, the "studies" and their grant-corporate exaggerations and the media sensationalist hype, are simply atrocious. I routinely pontificate to friends -- I'll spare you -- about American's lack of scientific knowledge to interperate the statistical significance of results and the media-driven hyperbolic conclusions. So any study needs to be taken with a bag of salt-- we know diacetyl sucks.
2) Anyone who is sucking down cheap Chinese juice made in some sweat pit in China probably has more to worry about than some DIY. There's been tons of posts about Chinese QC and I'll spare us the debate...
3) We need to understand that vaping burning juice into our mouths/sinuses/throats may not be the best thing in the long term and accept that--it is 200x better than smoking.
I'm not flaming the OP--It's good to see, but ANY study pro/con relating to the EC needs to really be evaluated as to the methodology and the validity of the claims.
This is why I'm also big against the "your body is changing" ECF attitude since Chinese fruit flavors tear/tore up my sinsues until I left them for JC. With vaping/DIY you need to ensure you and your body seem comfortable. If you're coughing or sinus bleeding or rashes it may not be your body--effects like that are a good way to guard against inhaling things that are damaging, especially with DIY. So if that TPA caramel is making you sneeze and bleed into a Kleenex ditch it!