This article (easily downloadable) demonstrates what patients on this forum well know: the strong link between Hashimoto's and Vitamin D.
Front. Endocrinol., 14 February 2020 | doi.org/10.3389/fendo.2020....
Correlation Between Hashimoto's Thyroiditis–Related Thyroid Hormone Levels and 25-Hydroxyvitamin D
Guanqun Chao*, Yue Zhu and Lizheng Fang*