I had bad bronchitis when I was a kid. They said it was asthmatic. It quit when I hit puberty, but I think it made my respiratory system weak. Seemed like colds always went to my chest and took about 3 weeks to completely leave me. I'm a lot more health conscious these days and can kick a cold much faster and without it going into my chest.

I also smoked for many years. Gave up the cigs about 12 years ago, but continued to smoke cannabis. A few years ago that started bothering me to the point where I was gonna quit. But it was just tight lungs and the chronic smoker's cough, not bronchitis. Then I discovered vapes. While too much heavy duty vaping can give me a case of tight lungs the next day, it's been much, much kinder than smoking, and I haven't had any chronic coughing or major lung issues since switching to vapor.

So for me, improving my health/immune system was more important for keeping my respiratory system up to par than whether I smoked/vaporized. Vapor is definitely much kinder to the lungs than smoke, and I've not heard of anyone having bronchitis with vaping unless, like you, they already had the problem.

As for vitamin absorption, tobacco use is a factor, but I've never heard anything about cannabis use causing problems. Sounds like your doc is the typical anti-cannabis type.