Thyroid diseases simply explained

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Do you have problems with your thyroid or suspect that you do? This guide explains the most common thyroid diseases in a simple way.

What is the function of the thyroid gland?

The thyroid gland (Glandula thyreoidea) is a hormone gland. It produces thyroid hormones. Hormones are messenger substances that travel through the bloodstream to the target organs, where they exert their effect. You can imagine this as if the blood from the thyroid gland transports many similar keys that fit into the right lock at the target organ. When they are unlocked, certain metabolic processes are set in motion.

The thyroid is located in the neck region, just below the larynx. It is in front of the windpipe. You may have felt it before. The thyroid is a butterfly-shaped organ because the two lateral lobes and their connection are shaped like a butterfly. In adults, the thyroid weighs between 18 and 30 grams, so it is relatively small. In women, it is usually heavier than in men.

The thyroid controls important bodily processes and acts as a hormone storage facility. Therefore, a wide variety of body and organ functions are impaired when thyroid function is impaired.

So what exactly happens in the thyroid?

Each lateral lobe consists of many small, vesicle-like structures (follicles), the walls of which are lined with a single layer of follicular epithelial tissue. The epithelial cells produce the thyroid hormones T3 and T4 and secrete them into the vesicle cavities. There they are stored in droplets. The two thyroid hormones are produced in reserve. This reserve lasts for up to two months. The exact function of the two thyroid hormones will be explained later.

What does the thyroid have to do with hypercalcemia?

The C cells are located between the vesicles. These produce the hormone calcitonin, hence the name. Calcitonin is always released when the calcium concentration in the blood is too high. The excess calcium is incorporated into the bones. If the calcium level is constantly too high, this is called hypercalcemia. This can lead to, among other things, cardiac arrhythmias.

How does the thyroid produce the hormones T3 and T4?

This requires the element iodine, which is absorbed through food. Like iron and zinc, iodine is one of the essential trace elements. Iodine is mainly found in sea water and the organisms that live in it. In contrast, the iodine content in groundwater and in our soil is very low. According to the recommendation of the German Nutrition Society and the Iodine Deficiency Working Group, different amounts of iodine should be consumed daily with food depending on age and needs.

Group of people


Iodine (micrograms (μg)/day)


0-4 months 40
4-12 months 80
1-4 years 100
4-7 years 140
7-10 years 140
10-3 years 180
Teenagers and adults 13-51 years 200
Adult 51 years and older 180
Pregnant women 230
Breastfeeding 260

The values ​​are guidelines. In some cases, the iodine requirement may be higher, for example in the case of an enlarged thyroid gland. However, this should be clarified medically.

Milk and dairy products, as well as sea fish, algae and seaweed, contain a lot of iodine. Bread and cold cuts are also rich in iodine. Iodine is absorbed through the intestines and then enters the blood.

The follicular epithelial cells fish the iodine out of the bloodstream like a sponge. After being absorbed into the cells, the iodine particles are passed on to the interior of the cell. There, the iodine is combined with the storage protein thyroglobulin with the help of enzymes (biocatalysts). This creates two variants, T3 and T4. If 3 iodine particles combine with thyroglobulin, the hormone triiodothyronine (T3) is created. In the other variant, 4 iodine particles are bound. Tetraiodothyronine (thyroxine), or more simply T4, is formed. T4 is much more common, at around 90%. T3, on the other hand, is only formed at 10%. T3 and T4 are stored in the follicles of the thyroid as long as there is no need for them.

The biologically active T3 is mainly responsible for the hormone effect. T4, on the other hand, is less effective, but is converted into T3 in the tissue of the target organ.

How is the production and release of thyroid hormones controlled?

The thyroid gland is not the only one that regulates the production and release of hormones. The brain is also involved, or more precisely a part of the diencephalon, the hypothalamus. The hypothalamus is the main control center for hormone production. Hormone production is subject to a control circuit. If the level of thyroid hormones (T3, T4) in the blood is too low, a message is sent to the hypothalamus. This stimulates the pituitary gland (another important control unit in the diencephalon) with the hormone TRH (therotropin-releasing hormone). This produces and releases the hormone TSH (thyroid stimulating hormone).

If TSH reaches the thyroid, this leads to an increased production of T3 and T4 and to their release from their intermediate storage (follicles) into the blood. The hormones reach all regions of the body and therefore also the diencephalon and thus the hypothalamus and the pituitary gland. If the T3 and T4 levels in the blood are too high, it inhibits the release of TRH and TSH in the diencephalon, which reduces the hormone production of the thyroid (negative feedback).

This may sound very complicated, but the basic principle is like a radiator. If the temperature in the room is too cold for me, I turn the radiator valve up. The radiator then heats up until the desired temperature is reached in the room. It then stops giving off more heat when a certain target value is reached. If it is too warm for me, I turn the valve down so that less heat is given off.

What is the function of the thyroid gland?

The thyroid produces, stores and releases thyroid hormones as needed. The organ is therefore involved in the regulation of iodine, calcium and overall metabolism.

The thyroid produces the following hormones:

  • Triiodothyronine (T3)

  • Tetraiodothyronine (thyroxine or T4)

  • Calcitonin

What effect do the hormones T3 and T4 have?

T3 and T4 have different functions:

The basal metabolic rate is increased. This increases heart activity, body temperature and the breakdown of fats and glycogen (the body's storage form of carbohydrates).

They also promote growth and brain maturation. This means that height and intellectual development depend crucially on the presence of the right amount of thyroid hormones.

The thyroid hormones have the following effects in detail. They promote:

  • the absorption of glucose (dextrose)

  • carbohydrate metabolism

  • oxygen consumption

  • the heat production

  • cholesterol reduction

  • the development of the central nervous system (brain and spinal cord), the sexual organs and the bone skeleton

  • muscle function

  • the heartbeat and blood pressure

At the same time, they inhibit the energy supply for muscle activity by:

  • the formation of adenosine triphosphate ATP (functions like an energy currency)

  • the storage of carbohydrates in glycogen (short-term energy storage in the liver)

  • the formation of proteins

  • the energy utilization

Thyroid control circuit

What problems can the thyroid cause?

The most common diseases include overactive thyroid (hyperthyroidism) and underactive thyroid (hypothyroidism).

In hyperthyroidism, the thyroid produces an excess of thyroid hormones. The cause is either hot nodules (these are autonomous tissue areas in the thyroid that constantly produce thyroid hormones independently of the control circuit) or an autoimmune disease in which the thyroid is abnormally stimulated by antibodies (Graves' disease).

As the cells burn nutrients more quickly, the body demands food more frequently. As a result, people suffering from hyperthyroidism are overly hungry, which can also manifest itself in food cravings. As the body produces more heat, they are often hot and suffer from outbreaks of sweat. This happens even in sub-zero temperatures, when others are already freezing. The organism is constantly running at full speed, making it difficult for those affected to fall asleep and sleep through the night. As they seem to be constantly on edge, nervous and easily irritable, they find it very difficult to relax. This often leads to aggressive outbursts, which are perceived by those around them as unpleasant and inappropriate. This often makes social interactions more difficult for those affected. On a physical level, high blood pressure and an accelerated heartbeat are common. Sometimes cardiac arrhythmias occur. Although drive is increased, performance drops. The body simply lacks recovery phases.

In contrast to hyperthyroidism, hypothyroidism means that the thyroid produces too little of the thyroid hormones T3 and T4. If you consider that metabolic processes are controlled by the thyroid hormones, it becomes clear that if there is a lack of T3 and T4, all body processes are slowed down.

What are the causes of hypothyroidism?

It is always the result of an illness or other disorder of the thyroid gland. In most cases, the thyroid tissue is destroyed by long-term inflammation, such as Hashimoto's thyroiditis. This causes the thyroid cells to slowly die and then no longer produce thyroid hormones. People usually develop thyroiditis between the ages of 30 and 50. Women are far more affected than men. In women, the symptoms often coincide with the menopause. The symptoms are then often overlooked because they are misinterpreted as menopausal symptoms. Around ten percent of people have a hereditary predisposition to thyroid inflammation. But not everyone develops Hashimoto's thyroiditis; it is only diagnosed in around a third. If Hashimoto's thyroiditis has broken out, autoimmune antibodies can be detected in the blood. It is not curable. Those affected must take thyroid hormones and selenium for life.

Why is selenium so important for the thyroid?

The thyroid gland is particularly sensitive to selenium deficiency. Selenium is needed for selenium-dependent enzymes such as glutathione peroxidase and thioredoxin reductase. These protect the tissue from self-destruction during hormone production because the oxidatively effective hydrogen peroxide is produced during the production of T4.

Like iodine, selenium is a trace element that the body cannot produce itself and therefore must be ingested with food. Germany is one of the selenium-deficient areas, i.e. there is often insufficient selenium in the soil and the foods produced with it. This effect is further exacerbated by poor eating habits such as the use of ready meals and fast food. Selenium deficiency can be determined by a full blood test. However, hypothyroidism can also be congenital. Most newborns are completely missing their thyroid gland. Either too little thyroid tissue is produced during pregnancy, or in rarer cases there is an extreme iodine deficiency. After an operation on the thyroid, in which the thyroid gland is either completely or partially removed, hypothyroidism occurs. This can be easily treated by administering synthetically produced hormones. There is another form of hypothyroidism, however, in which the production of thyroid hormones is not impaired, but the pituitary gland does not secrete enough TSH. As already explained, TSH stimulates the production of T3 and T4 in the thyroid gland. As a result, the thyroid produces too few hormones. This is known as secondary hypothyroidism.

In contrast to hyperthyroidism, those affected are extremely sensitive to cold. Since the metabolism is slowed down, less heat is released when food is converted into energy. Those affected suffer from constant tiredness and lack of motivation. This makes it harder for them to concentrate and less efficient. The cause of all these symptoms is the lack of energy provided by the lack of thyroid hormones. On a physical level, this is also reflected in movements and a slowed heartbeat. Water retention often occurs in all possible places on the body, which is known as myxedema in the case of hypothyroidism. It is particularly noticeable on the patient's face, which gradually swells. Since food is less effectively utilized, patients gain weight even though they are not eating more than usual. Skin and hair are also affected. Hair becomes dull and skin becomes dry. Fingernails often break off. Women can experience irregular periods and infertility. Men can develop impotence and infertility. On a psychological level, depressive moods can occur. Those affected often isolate themselves from the outside world because they find contact with other people too stressful. This self-imposed isolation worsens the patient's condition even further.

What is a goiter?

When the thyroid gland enlarges, a goiter develops. Often, the cause is iodine deficiency, but not always. It is important to differentiate carefully. In the Alpine region, women used to wear a goiter band. This was used to conceal a goiter or scars on the neck. Goiters, known by doctors as struma, are still relatively common today. According to statistics, at least 20 million people in Germany suffer from it.

As already mentioned, the thyroid needs iodine to produce the hormones T3 and T4. If the thyroid does not have enough iodine available, it tries to compensate for this deficit by growing larger. If there is uniform growth in all areas, this is called diffuse goiter. Often, however, only individual areas become larger. This causes thyroid nodules to form. Doctors then refer to this as nodular goiter. If the goiter reaches a certain size, it can be felt from the outside. The patient then has difficulty breathing and swallowing, for example, because the windpipe and esophagus are constricted. The treatment of choice here is surgery. If nodular goiter is associated with autonomous nodules, radioiodine therapy can also help. Radioactive iodine is administered to the body, which destroys the autonomous nodules. However, this is not harmful to humans, as the radioactivity is not particularly high and the radioactive iodine decays relatively quickly. Especially with autonomous nodules, it is even harmful to consume more iodine than is present in food, as this increases the overactivity. In this case, you should also avoid iodized table salt. If the goiter is still relatively small and there are no nodules, taking iodide tablets or appropriate nutritional supplements is sufficient.

How dangerous is thyroid cancer?

Thyroid cancer is a relatively rare form of cancer and is often one of the less dangerous. Carcinomas (certain forms of cancerous tumors) usually grow slowly and only form metastases after a long period of time. This refers to differentiated carcinomas, which are far more common than undifferentiated ones. Undifferentiated carcinomas are particularly dangerous and tend to form metastases quickly. Undifferentiated carcinomas no longer have any similarities with the original tissue and grow very quickly, including into the blood and lymph vessels. This promotes the formation of metastases.

The treatment of choice is surgery followed by radioiodine therapy. Chemotherapy is usually unsuccessful in treating thyroid cancer. Radioiodine therapy is preferable to radiation therapy because it also damages healthy tissue in the neck area (including the windpipe and esophagus).

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