I've read hundreds of dust mite studies, and this is the conclusion I came to, but it's difficult to put in a direct single argument with a citation that most people would require to accept it. I also got dust mites entirely out of my home and my chronically low vitamin D was resolved without a change in lifestyle or supplementation.

But I'll do my best to share some of the steps toward this conclusion:

#1. There is a body of molecular research showing dust mite allergens directly damage the immune system, most importantly once you inhale their fecal pods, they cause epithelial permeability in the lungs. (this study is a good overview of several ways it directly damages the immune system, all of which are totally unrelated to type 1 hypersensitivity, btw: https://www.jacionline.org/article/S0091-6749(18)30848-0/ful...)

#2. There are challenge studies that show dust mites directly causing eczema symptoms after inhalation, which shows that dust mite allergens can act on areas other than the respiratory system, probably by entering the blood stream. Of course there are also challenge studies for asthma. (here's a paper arguing for causal role in asthma https://www.atsjournals.org/doi/full/10.1164/rccm.200811-175...)

#3. All of the major allergic diseases(asthma, eczema, rhinitis, and although it is not as well studies, I believe IBS) have epithelial damage and increased allergy as a core feature of the disease. #1 and #2 are good evidence that dust mites play a causal role in these diseases

#4. From asthma and epithelial permeability in the lungs you can get to worse outcomes from flu and covid etc, from rhinitis you can get to worse sleep and worse mental health etc and reach a large number of health outcomes.

#5. It's true that people with allergy suffer worse from all these problems, but so much damage has already been done before you even get to Type 1 hypersensitivity, but that's another story.

So basically, dust mites directly damage your immune system in the lungs, skin, nose, eyes, guts(and maybe more?), create a sustained immune response, and leads to a multitude of other bad health outcomes.

And since low vitamin D is associated with dust mite sensitization((https://www.worldallergyorganizationjournal.org/article/S193...) , it's also associated with all those other bad health outcomes that are actually caused by dust mites.

People have a mental model that vitamins are at the root level of causality, and therefore don't consider that vitamin D could also be caused by dust mite exposure.

IgE levels are inversely associated with vitamin D: https://www.nature.com/articles/s41598-020-77968-1

But supplementing vitamin D doesn't lower IgE: https://publications.aap.org/pediatrics/article/150/Suppleme...

And of course high IgE is directly caused by exposure to dust mites if you're sensitized.

I don't know the specific mechanism by which they cause low vitamin d, but two possibilities are that #1: the high and sustained immune response your body runs from constant dust mite exposure consumes vitamin D and acts like a leaky bucket. #2: dust mites somehow disrupt vitamin d production in the skin(e.g. there was one study showing https://www.jacionline.org/article/S0091-6749(13)01768-5/ful...)

We're learning more about what Vitamin D does