The thyroid gland is located at the front of the neck just below the Adam's apple (larynx). It is butterfly-shaped and consists of two lobes located either side of the windpipe (trachea). A normal thyroid gland is not usually outwardly visible or able to be felt if finger pressure is applied to the neck.
The thyroid gland produces hormones that regulate the body's metabolic rate controlling heart, muscle and digestive function, brain development and bone maintenance. Its correct functioning depends on a good supply of iodine from the diet. Cells producing thyroid hormones are very specialised in extracting and absorbing iodine from the blood and incorporate it into the thyroid hormones.
The signal comes from a small gland located at the bottom of our brain called the pituitary gland. The pituitary gland produces and sends out a hormone called thyroid-stimulating hormone (TSH). TSH then tells the thyroid gland how much hormones to produce and secrete. TSH levels in your blood are rising and falling depending on your body’s needs to produce more or less thyroid hormones.
There is a third actor involved in this communication. The pituitary gland responds either directly to the thyroid hormones in the blood, but it also responds to signals from the hypothalamus, which sits above the pituitary gland as part of your brain. The hypothalamus releases its own hormone thyrotropin-releasing hormone (TRH). TRH in turn stimulates the release of TSH in the pituitary, which then signals to the thyroid gland.
This whole network is also referred to as the hypothalamic-pituitary-thyroid axis (HPT) and it adapts to metabolic changes and your body’s needs.
The thyroid gland produces thyroxine (referred to as T4), which is a relatively inactive prohormone. The highly active hormone is triiodothyronine (referred to as T3). Collectively, thyroxine and triiodothyronine are referred to as the thyroid hormones. The thyroid gland produces just 20% of the high active T3, but it produces 80% of the prohormone T4. Once secreted by the thyroid, specific enzymes in other tissues like the liver or kidneys may transform T4 in to the active hormone T3.
In addition, there are other hormone-producing cells within the thyroid gland called C-cells. These cells produce calcitonin. Calcitonin plays a role in regulating calcium and phosphate levels in the blood, which is important for your bone health and maintenance.
Normally the thyroid gland produces the exact number of hormones needed to keep your body’s metabolism running and in balance. As described earlier, hormones secreted by the pituitary gland (TSH) stay constant in your blood circulation, but their levels may increase or decrease when T4 levels in the blood are changing. This hypothalamic-pituitary-thyroid feedback loop keeps the levels of T4 in your blood stable and reacts to small changes immediately.
However, there are several disorders associated with the thyroid gland with most problems concerning the production of thyroid hormones. Either the thyroid gland produces too much hormone (called hyperthyroidism) or your thyroid doesn't produce enough hormone (called hypothyroidism), resulting in your body using energy faster or slower than it should.
Typical symptoms for hyperthyroidism is weight loss, fast heart rate, high irritability/nervousness, muscle weakness and tremors, infrequent menstrual periods, sleep problems, eye irritations and heat sensitivity.
Symptoms for hypothyroidism is the contrary of hyperthyroidism such as weight gain, slower heart rate, fatigue, more frequent and stronger menstrual periods, forgetfulness, dry skin and hair, hoarse voice and intolerance to cold. In addition, hypothyroidism is often accompanied by an enlargement of the thyroid gland known as goitre.
On a worldwide scale, approximately 200 million people have some form of thyroid disease. People of all ages and races can get thyroid disease. However, women are 5 to 8 times more likely than men to get problems with their thyroid function.
There are various different factors causing hyper- and hypothyroidism.
The following conditions cause hypothyroidism:
Thyroiditis is an inflammation of the thyroid gland. This can lower the number of hormones produced.
A special form of thyroiditis is Hashimoto's thyroiditis. This is a genetic disorder caused by diseases of the immune system and can be passed from one generation to the other. In addition, thyroiditis can occur in women after giving birth also referred to as postpartum thyroiditis. It is usually a temporary condition and occurs only in 5-9% of woman giving birth.
Nutrition also impacts your thyroid functions. Iodine deficiency can cause hypothyroidism. This is a worldwide problem affecting approximately 100 million people. As mentioned earlier, iodine is used by the thyroid gland to produce hormones.
The following conditions cause hyperthyroidism:
Graves' disease is a condition where the entire thyroid gland might be overactive and produce too much hormone. Your thyroid gland might be enlarged. This problem is also called diffuse toxic goitre.
Thyroiditis (inflammation) can also cause the opposite and trigger the release of hormones that were stored in the thyroid gland. This uncontrolled release of thyroid hormones causes hyperthyroidism for a few weeks or months. It may occur in women after childbirth.
In contrast to iodine deficiency, excessive iodine intake may have negative effects on your thyroid. Excessive iodine is found in a number of drugs such as Amiodarone, Lugol's solution (iodine) and some cough syrups. This might cause the thyroid to produce either too much or too little hormone in some individuals.
The before mentioned problems affect the production of thyroid hormone (either too much or too little). However, problems concerning the thyroid gland can be very distinct. Swelling and lumps can occur within the thyroid gland. Such nodules can be harmless, but some can cause the production of hormones or even be cancerous. In some cases, such as cancer, the thyroid is removed. You can live without your thyroid, but you need to take medicine daily to substitute the hormones produced by your thyroid gland.
Iodine is most essential to maintain a healthy thyroid. Iodine is the critical ‘ingredient’ for the production of thyroid hormones. We don’t need a lot of iodine, it is said that “one teaspoon of iodine is enough for a lifetime”. Nonetheless, the daily and constant supply of this micronutrient is important. Too much iodine at once is counter-productive and causes your thyroid to produce less hormones. The best way to get your daily dose of iodine is through eating healthy foods like seafood and dairy products. In addition, iodized salt is a good source and you can use it to season your food. Nowadays, iodine is added to salt to combat goitres (caused by hypothyroidism).
Last reviewed: Mar 2018