I ran across some articles pointing to low levels of D and affecting levels of tyrosine hydroxylase and thereby adversely affecting adrenal hormones. I'm not at all well versed on biochemistry so I don't even know what other forms of tyrosine are affected by low d levels. I'm taking an educated guess that it probably does affect the thyroid too, since tyrosine is involved in thyroid hormones as well as adrenals. I do know that low levels of D affect the immune system and cause symptoms of fatigue, Arthritis like pain, bone and muscle pain. It seems like every day, researchers are finding out more stuff about vitamin D and how important it is to our bodies.
Please check out Janie's Stop the thyroid madness site out. She packs a lot of useful info there. I do know that until you address things like low ferritin and adrenal fatigue, you won't have much success optimizing thyroid meds. I speak from experience. I had to address my high cortisol before I started feeling better. My ferritin level was 48 and one of my docs (I've been through many until I found the one that's been able to actually help me) thought because it was in range it was fine. WRONG!! I found out at Janie's site that ferritin levels must be above 50, ideally 70-90 before the thyroid meds get from the blood to the thyroid. Until the ferritin level gets to 70 the thyroid meds will just circulate in the blood making you feel hyper.