This is similar to my lived experience. I was diagnosed with Hashimoto's 3 years ago. I was lucky to find a great doctor that specialized in it. He put me on 15000 IU / day for 3 months because I was so severely low in addition to having high antibodies. Within 3 months my levels were so much better. I still take 10000 IU / day along with selenium, iron, fish oil and good diet/exercise and all my levels have been in check for 2 years :)