I have friends and family who constantly make me aware of some news article they saw about the "possible" dangers of vaping - but I'll be honest, I have yet to see anything other than scare tactics and when you read them they have absolutely no evidence that they are "bad" for you, just that there is supposedly no strong evidence that says it isn't. It's unfortunate, because the public sees the headlines and they never read the article. The only truly dangerous things I have ever read have been about people who make shoddy mods and start a fire or explosion with them.
Here's how I look at it - we know the dangers of cigarettes, which have 1000's of chemicals that are known to kill people. I know exactly what is in my juice - distilled water, glycerin, sweetener, flavor, nicotine. I can count them on one hand. Water isn't dangerous (if it is, we are all screwed), glycerin is in zillions of products we use every day, and the sweetener and flavors that are in the juice I use are safer/purer than what you find on the grocery shelf. As to the nicotine - people have a horrible understanding of it, because it's so identified with tobacco. There is nothing inherently bad about nicotine, any more than caffeine, in these amounts.
So, I may not have studies to prove it - but personally, I don't need them. Five well-known chemicals, inhaling water vapor - it's certainly a heck of a lot better than analog smoking, and as a life-long asthmatic who feels BETTER and can breathe easier after I vape than before - it's really difficult for me to see what the worry is, except for the folks who won't be making money off of my addiction/health problems due to tobacco use.