I think meditation's primary effect, perhaps its only noticable effect for most, is lowered anxiety via learning how to focus thought which tends to lead to less worrying and such. Less anxiety means better sleep, earlier bedtimes, less cortisol in the body, etc. Over time these can affect us physically in an beneficial way.

An eight week mediation course shrinks the part of the brain involved in anxiety:

https://www.washingtonpost.com/news/inspired-life/wp/2015/05...

From an anecdotal perspective I found taking a anti-cortisol herb (Rhodiola and Ashwaganda) gave me a comparable, but stronger, effect compared to what 30-45 minutes daily meditation gave me.

Meditation lowers cortisol:

https://www.ncbi.nlm.nih.gov/pubmed/23724462

Sort of. I have an autoimmune disease affecting my thyroid. When the thyroid is in hyper mode, I tend to get anxiety and panic attacks. Meditation has helped me a lot with those if the flareup is not severe.

Because the result of meditating can be less stress overall. And stress is known to "aggravate" the immune system. It might lead to better wellbeing when talking about autoimmune diseases. But they do progress slowly so other factors could also be at play here.

Unfortunately, not much is known about autoimmune diseases. There are a few theories(strong immune system, weak immune system, virus, contaminants..) but nothing conclusive yet. I try to stick to published and peer reviewed research when looking up information rather than mommy bloggers but not much is known for these diseases.

Overall, I'd say introducing meditation as a frequent practice has been a positive thing in my life. Whether or not it helps with any chronic disease.