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Iodine deficiency. Worldwide, the most common cause of goitre formation is sustained dietary iodine deficiency, this is referred to as endemic goitre.
Thyroid hormones have a high iodine content, so if the thyroid gland does not have enough iodine it cannot produce thyroid hormone. As a result, it secretes too little hormone, which leads to hypothyroidism.
When the pituitary gland detects low levels of thyroid hormone, it sends a hormone signal to the thyroid gland to stimulate it: thyrotropin (thyroid stimulating hormone, TSH) This stimulates the thyroid to produce the necessary amount of thyroid hormone, causing it to increase in size and the goitre to form.
In developed countries, like Spain and, in general, the countries in the European Union and the United States, iodine deficiency is no longer a common problem thanks to epidemiological, socio-health and population education measures that promote the consumption of iodised salt. However, there are still areas and communities where iodine deficiency remains a problem.
Iodine is found naturally in sea products as well as in plants that grow in iodine-rich soils. Salt for daily use is often supplemented with iodine and known as iodised salt.
Chronic autoimmune thyroid diseases (Hashimoto's thyroiditis and Graves' disease).
Chronic autoimmune thyroiditis, or Hashimoto's thyroiditis, is a common cause of goitre formation. This is an autoimmune disease in which the patient's own immune system attacks the thyroid gland. When the thyroid gland becomes severely damaged, the thyroid is unable to ensure sufficient hormone supply. As in iodine deficiency, the pituitary gland detects hypothyroidism and synthesises more TSH to stimulate the thyroid and the production of thyroid hormones. If the disease progresses slowly and allows the thyroid to grow, the process will lead to the formation of a goitre.
Graves' disease. In this case, the immune system produces a thyroid-stimulating antibody, called TSH receptor antibody (TRAb) or thyroid-stimulating immunoglobulin (TSI). Like TSH, TSI and TRAb stimulate the thyroid gland to increase the production of thyroid hormones, leading to the development of a goitre. The pituitary gland detects the excessive amount of hormone in the blood and blocks TSH secretion to slow down the thyroid, but the thyroid gland continues to respond to TSI, growing further and overproducing hormones. Graves' disease therefore results in diffuse goitre and hyperthyroidism.
Other causes of goitre
Goitres secondary to a genetic deficit in the synthesis, transport or function of thyroid hormones. These represent a third cause of thyroid enlargement that often begins in childhood. It is caused by absolute or functional deficiency of thyroid hormones, thyroid enlargement and the appearance of a goitre referred to as "dyshormonogenetic" or "dysenzymatic".
There are many other less frequent causes related to chronic consumption of goitrogenic foods (chronic consumption of cassava, also known as manioc); infections or infiltrative diseases that accumulate substances in the thyroid (amyloidosis, sarcoidosis) or that affect hormone production (lithium); and some due to either malignant or benign tumours.
Mireia Mora PortaEndocrinologistNutrition and Endocrinology Department
Published: 2 June 2021
Updated: 2 June 2021
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