I do know that nicotine will raise blood pressure, which could cause a stroke or heart attack to anyone who may have heart disease. In the future they may find vaping to cause some issues. I just can not see it being more dangerous than smoking, ever.
A lot of sources categorically say that nicotine raises blood pressure, but there is some doubt. Some studies suggest it doesn't. I also tested my own blood pressure using 2 good meters before and after vaping deliberately large doses of nicotine, and found no significant change. Nonetheless, I'd advise any vaper concerned about their blood pressure to take the risk seriously at least until they've reliably tested it out for themselves. It's still likely to be less of a risk to blood pressure than tobacco smoking of course.
I think one logical approach to minimising any other potential ill effects of vaping (for nicotine addicts) is to use a high nicotine concentration so that the user doesn't need to inhale so much of the additives to get whatever nicotine dose their addiction demands (as well as helping the equipment to last longer
). That may require some self-discipline though, as in my experience nicotine has a nasty habit of getting the user to increase the rate of consumption over time, so the wrong person could end up consuming more nicotine and becoming more strongly addicted. And I wouldn't say that nicotine has no other harmful effects apart from blood pressure. OTOH it's known that smoking can delay the onset of Alzheimer's and it's a mild antidepressant, so maybe vaping can do the same thing.
All in all, I'd not recommend vaping to anybody except as an alternative to using tobacco, but then I guess it's pretty rare for real people to avoid all pleasurable things that are known to be riskier than vaping is so far considered to be, so I wouldn't be over-concerned either. Just my 2 cents.