Hyperthyroidism can be caused and/or triggered by a number of conditions related to the thyroid gland and the chemicals that it releases. More specifically, the two main hormones involved in hyperthyroidism are thyroxine and triiodothyronine, or T4 and T3 respectively. Together, these hormones influence every cell in the body – from maintaining the rate at which the body uses fats and carbohydrates, to controlling body temperature and influencing heart rate, to regulating the production of protein as well as the amount of calcium in the blood.
Usually the thyroid will release the correct amount of hormones, but in some instances it produces too much T4. When the body ends up producing excess thyroxine, it may be due to Graves’ disease, hyperfunctioning thyroid nodules, or thyroiditis. The first of these is an autoimmune disorder which is often triggered by stress, smoking, radiation to the neck, certain medications, and infectious organisms such as viruses. Scientifically speaking, Graves’ disease is when the body makes an antibody called thyroid stimulating immunoglobulin (TSI). These TSIs then mimic the action of thyroid stimulating hormone (TSH), leading to excess secretion of thyroxine and triiodothyronine.
Hyperthyroidism can also be caused by hyperfunctioning thyroid nodules, other names for which include toxic adenoma, toxic multinodular goiter, and Plummer’s disease. An adenoma is an overgrowth of normal thyroid tissue while a multinodular goiter simply refers to an enlarged thyroid gland. The word ‘toxic’ in front of both of these terms means that the nodules are active and functioning autonomously. That is, they are producing thyroid hormone with no regard for normal feedback control mechanisms. This can then lead to the development of hyperthyroidism, as can thyroiditis, an often temporary condition that is characterized by inflammation of the thyroid.
Thyroiditis can be broken down into several different types, namely subacute thyroiditis, postpartum thyroiditis, and silent thyroiditis. Subacute thyroiditis is a condition involving an enlarged and painfully inflamed thyroid. While experts are not entirely sure what causes this type of thyroiditis, they believe it may be related to an infection caused by either a virus or bacteria. Postpartum thyroiditis develops after a female gives birth and is considered to be a fairly uncommon condition. Silent thyroiditis is a painless variety, despite the fact that the thyroid may still be enlarged, and is thought to be an autoimmune condition.
Additional causes of hyperthyroidism include excessive doses of thyroid hormone, excessive consumption of iodine, and tumors in the body’s reproductive organs, specifically the ovaries and testes. High levels of thyroid hormone can create problems with a rapid or irregular heartbeat, plus it can lead to weak bones or osteoporosis. Excessive iodine intake, on the other hand, may cause similar symptoms to those associated with iodine deficiency, in addition to thyroiditis and thyroid papillary cancer. Some products with surprising amounts of iodine include medicines, cough syrups, seaweed, and seaweed-based supplements. For example, the heart medicine amiodarone contains a lot of iodine. Other medicines can interact with thyroid hormone medicine in such a way that it raises thyroid hormone levels above what is desired.
Resources:
1) https://www.medicinenet.com/hyperthyroidism/article.htm
2) https://www.niddk.nih.gov/health-information/endocrine-diseases/hyperthyroidism
3) https://www.mayoclinic.org/diseases-conditions/hyperthyroidism/symptoms-causes/syc-20373659
4) https://www.endocrineweb.com/conditions/hyperthyroidism/hyperthyroidism-overview-overactive-thyroid