What is the most common cause of hypothyroidism?

The most common cause of hypothyroidism is Hashimoto thyroiditis. This autoimmune disorder results from the immune system mistakenly attacking the thyroid gland, leading to inflammation and chronic damage. Over time, the gland becomes less effective at producing thyroid hormones, ultimately resulting in hypothyroidism.

Hashimoto thyroiditis is particularly significant because it is not only prevalent but also often occurs in middle-aged women. The condition can be asymptomatic in its early stages, which sometimes leads to delayed diagnosis unless routine screening occurs.

While iodine deficiency is historically a common cause of hypothyroidism in certain parts of the world, it has become less prevalent in areas with adequate dietary iodine intake. Other options, such as Graves disease, are more commonly associated with hyperthyroidism rather than hypothyroidism, and thyroiditis can refer to various types of thyroid inflammation but is not specific to the autoimmune aspect represented by Hashimoto's. Therefore, Hashimoto thyroiditis stands out as the leading cause of hypothyroidism in the general population.