Suppressed breathing -- not technically asthma, but worrisome enough -- that worsened with vitamin D supplements responded to vitamin K supplements and vagus nerve stimulation exercises.
Update July 2022: This problem improved a lot when I started doing vagus nerve stimulation exercises. I also noticed that on days following activity that involved lifting very heavy (for me) items, my breathing would be easier.
About six years ago I realized I was getting very tired every time I visited a home with a resident cat. It was annoying but easy enough to avoid. Then, after a round of weekly 50,000 IU vitamin D doses, I got a day-long burning-lung, wheezing, iron-vise-on-the-ribs reaction that made me wonder if my appointment with my maker had been moved up.
Off I was sent to yet another fancy-ass specialist for blood tests and breathing into a bellows thing and x-rays, which had to be taken twice because I apparently have “really long lungs” that did not fit on the x-ray plate. The diagnosis was a one-off asthmatic allergic reaction.
Thinking the big vitamin D dose was just too big, I tried smaller doses of 1,000 IU, but the effects were similar. I then considered the possibility that it had overwhelmed my levels of the competing fat-soluble vitamins A and E. Vitamin A did help slightly, but not enough.
It finally occurred to me that I had forgotten about vitamin K, another fat-soluble vitamin. According to PubMed, a 1970s Japanese study treating asthma with vitamin K was quite successful.
I took 1,000 IU of vitamin K2 (menaquinone 7) for two weeks before my next attempt at vitamin D again, this time working up to 6,000 IU. Voila! Almost no reaction, and iron got rid of that. Eventually I could do without the iron entirely. I guess that since both vitamin K and iron are involved in oxygen transport, they can back each other up to a point. It just took a while for the vitamin K to build up to needed levels.
I have yet to test this on feline exposure. Since that seems to be an immune system issue, I’m guessing that something else is involved.