What is the most common cause of thyroid disease?

• A. Autoantibodies
• B. Iodine deficiency
• C. Radiation exposure
• D. Bacterial infection

Answer: (A)

Autoimmune processes are the most common way thyroid dysfunction arises. The thyroid becomes a target of the immune system, and antibodies against thyroid components—such as thyroid peroxidase and thyroglobulin—drive inflammation and disrupt hormone production. These autoantibodies underpin two common diseases: Hashimoto’s thyroiditis, where antibodies lead to destruction of the gland and usually hypothyroidism, and Graves’ disease, where stimulating antibodies target the TSH receptor and cause hyperthyroidism. Because autoimmune thyroid disease is widespread and accounts for the majority of thyroid dysfunction in many populations, antibodies against thyroid antigens are the leading cause.

Iodine deficiency can cause goitre and hypothyroidism, especially in regions with low iodine intake, but it’s not as globally prevalent in modern, iodine-sufficient settings. Radiation exposure and bacterial infection do occur but are much less common causes of thyroid disease.