evidence: The thyroid gland plays a major role in metabolism, hormone regulation, and body temperature. When a person has Hashimoto’s, their thyroid is chronically inflamed and cannot function as well as a healthy thyroid. [...] Several studies have found a link between low vitamin D levels and Hashimoto’s. Anyone diagnosed with Hashimoto’s thyroiditis should be sure to get their vitamin D levels tested. Vitamin D can be produced in the body during sun exposure or consumed through food or supplements.