What causes hypothyroidism (underactive thyroid)?

From the Guidelines

Hypothyroidism is a condition characterized by an underactive thyroid gland, which can be caused by various factors, including autoimmune disorders, such as Hashimoto's thyroiditis, radiation therapy, or surgical removal of the thyroid gland 1. Certain medications, including lithium and amiodarone, can also induce hypothyroidism, particularly with long-term use exceeding 6-12 months 1. Additionally, iodine deficiency or excessive intake of iodine can disrupt thyroid function, leading to hypothyroidism.

Common Causes of Hypothyroidism

• Chronic autoimmune (Hashimoto) thyroiditis is the most common cause of hypothyroidism in the United States 1
• Radiation therapy and surgical removal of the thyroid gland can also lead to hypothyroidism
• Medications, such as lithium and amiodarone, can induce hypothyroidism, particularly with long-term use
• Iodine deficiency or excessive intake of iodine can disrupt thyroid function, leading to hypothyroidism

Risk Factors for Hypothyroidism

• Female sex
• Advancing age
• White race
• Type 1 diabetes
• Down syndrome
• Family history of thyroid disease
• Goiter
• Previous hyperthyroidism
• External-beam radiation in the head and neck area 1

From the Research

Causes of Hypothyroidism

The causes of hypothyroidism can be varied and include:

• Autoimmune diseases, such as Hashimoto's thyroiditis 2, 3, 4, 5
• Radiation therapy 2, 3, 4
• Thyroid gland removal surgeries 2, 3, 4
• Certain medications, such as lithium carbonate and amiodarone 3, 4
• Congenital thyroid disorders 3, 5
• Dietary iodine deficiency, particularly in areas where iodine deficiency is common 3, 4
• Pituitary and hypothalamic disorders 3, 5
• Previous radio-iodine or surgical treatment of hypothyroidism 5

Other Factors

Other factors that may contribute to the development of hypothyroidism include:

• Age, with older adults being more likely to develop hypothyroidism 2, 3, 5
• Sex, with women being more likely to develop hypothyroidism than men 2, 3, 5
• Iodine intake, with excessive or restricted iodine intake potentially contributing to hypothyroidism 6

Underlying Conditions

Underlying conditions that may increase the risk of developing hypothyroidism include:

• Autoimmune thyroiditis, such as Hashimoto's thyroiditis 2, 3, 4, 5
• Thyroid gland damage or destruction, such as from radiation therapy or surgery 2, 3, 4
• Pituitary or hypothalamic disorders, such as hypopituitarism or hypothyroidism due to pituitary or hypothalamic disease 3, 5