Hypothyroidism & Hyperthyroidism

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Last Medical Review: March 26, 2020
Medically Reviewed by Dr. David Costa Navarro
Hypothyroidism & Hyperthyroidism (March 26, 2020)

What is the thyroid?

The thyroid is a gland located in the front of the neck that produces hormones. Thyroid hormones play an important role in every tissue of the organism, intervening both in the fundamental stages of body development and in all metabolic reactions, through the increase of protein synthesis and oxygen consumption.

How does it work

For the synthesis of thyroid hormones, T3 or triiodothyronine and T4 or tetraiodothyronine or thyroxine, iodine taken with food is essential. The maintenance of an adequate rate of thyroid hormones in the blood depends both on a correct intake of iodine with the diet, and on the proper functioning of a control system represented by the pituitary gland, a gland located in the center of the skull that produces TSH (Tyroid stimulating hormone), and the hypothalamus, a small formation placed above the pituitary gland, which produces TRH (Tyreotropine Realizing Hormone). The alteration of this balance leads to two opposite pathological conditions: hyperthyroidism or hypothyroidism.


When the thyroid “works too much” and, in the blood, the concentration of circulating hormones is high, it is called hyperthyroidism. This condition causes an acceleration of all metabolic reactions in which thyroid hormones intervene. The most frequent symptoms include: weight loss, acceleration of the heart rhythm, nervousness, hand tremor, anxiety, insomnia, muscle weakness, excessive sweating. Usually the patient has protruding and painful eyeballs and an enlarged gland (goiter). Hyperthyroidism, more common in women than men, can have several causes. The most frequent is Basedow’s disease, which occurs mainly in young people, a disease in which antibodies that stimulate the thyroid gland to produce an excessive amount of hormones are formed. Among the conditions causing hyperthyroidism, we can mention the toxic multinodular goiter, in which nodules that produce high quantities of hormones are formed, and the toxic solitary adenoma, a benign tumor, in which a group of thyroid cells becomes hyperactive. Some medications, such as amiodarone and lithium, can also cause hyperthyroidism.


When the thyroid “works very little”, that is, it produces an insufficient amount of hormones, it is called hypothyroidism. Hypothyroidism can have an insidious onset and the faded symptoms can go unnoticed for some time. The most frequent include apathy, weight gain, constipation, slow heart rate, fatigue, depression, particular sensitivity to cold and abundant menstrual cycle. The most frequent cause of hypothyroidism is a disease called Hashimoto’s thyroiditis, in which antibodies produced by our body destroy thyroid cells, thus reducing the functionality of the gland. Hypothyroidism may also be due to radioactive iodine treatments or be the consequence of thyroid surgery. Hypothyroidism can also appear following childbirth, causing a depressive state that can be confused with postpartum depression. When due to iodine deficiency, hypothyroidism can resolve itself by increasing the intake of this substance with food: fish and seafood are rich in iodine.

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