TH and Hashimoto thyroiditis: Hypothyroidism is a common endocrine disorder resulting from a deficiency of thyroid hormones (TH). Worldwide, iodine deficiency is the most common cause of hypothyroidism; however, in Poland and other areas of adequate iodine intake, chronic autoimmune thyroiditis—the Hashimoto’s disease also known as the Hashimoto thyroiditis is the primary reason for hypothyroidism4,5.