Harpy
There is a strong corrolation between Vitamin D deficiency and many Autoimmune diseases & cancers, but that is not to say that it is a causal relationship, just that very often both conditions are present at the same time.
Vitamin D is a modulator of the adaptive immune response by stimulation of Regulatory T-Cells, so there is the possibility that low Vit D levels may leave the door open for an autoimmune response, but low Vit D levels will certainly be an aggravating factor when there is an autoimmune disease present.
So the main thing is, knowing that there is a risk of low Vit D levels when GD is present, to get levels checked and consult with a practitioner to normalize levels by supplementation and/or direct sun exposure.
Note Vitamin D is produced in the skin by exposure to UVB rays which are strongest in the middle of the day (10-2), they are also the ones that are responsible for the sunburn response, which appears to be an indicator that you have maxed out on Vitamin D, conversly the UVA rays are the ones that penetrate much deeper, produce the tanning effect (melanin production) and cause the greater skin damage. Most guidelines say 15-20 min of daily good body exposure to the sun is plenty, so don’t get burned, this can produce 20-30,000 IU of Vitamin D. Obviously do not apply sunscreen for this brief time and also do not have a shower immediately after as the Vit D is close to the surface and needs time to be absorbed by the body.