Which condition is the most common cause of hypothyroidism in the United States?

Hashimoto's thyroiditis is indeed the most common cause of hypothyroidism in the United States. This autoimmune disorder leads to the destruction of thyroid tissue, resulting in decreased production of thyroid hormones. In Hashimoto's thyroiditis, the body's immune system mistakenly attacks the thyroid gland, causing inflammation and dysfunction. Over time, the thyroid gland may become unable to produce sufficient amounts of hormones, leading to hypothyroidism.

This condition can manifest with various symptoms such as fatigue, weight gain, cold intolerance, and depression, among others. The diagnosis is typically confirmed through blood tests measuring thyroid hormone levels and the presence of thyroid antibodies. Identifying Hashimoto's thyroiditis as the leading cause of hypothyroidism underscores the importance of recognizing autoimmune processes in thyroid disorders.

In contrast, other conditions listed do not represent the primary causes of hypothyroidism. Graves' disease is primarily associated with hyperthyroidism rather than hypothyroidism. Thyroid cancer, while sometimes leading to hypothyroidism after treatment (like surgery or radioactive iodine), does not account for the overall incidence of hypothyroidism. Diabetes mellitus, although it can occur concurrently with autoimmune thyroid disorders, is not in itself a primary cause of hypothyroidism.