Introduction and occurrence

Thyroid scintigraphy for functional assessment of the thyroid gland

Iodine is a chemical element with the element symbol I and belongs to the group of halogens. The chemical element iodine occurs naturally in bound form in the form of its salts. Examples of the salt forms of iodine are potassium iodide and sodium iodide. Iodine is supplied with food and is an indispensable element for the animal and human body. Because of this, it is counted among the trace elements. The German Nutrition Society (DGE) indicates the daily need for iodine at 180 µg to 200 µg. Pregnant and breastfeeding women should take in a little more with 200-250 µg daily. For children, the DGE recommends an intake of 40-200 µg per day. In actual fact, however, the intake is lower; it is estimated that adults consume around 120 µg iodine per day. Coastal areas are rich in iodine in the form of fish and seaweed.

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This article might interest you: Potassium iodide as a thyroid drug

In addition, iodine is also in iodized table salt and in drugs, like Amiodarone, one Antiarrhythmicwhat to treat numerous Cardiac arrhythmias is used. Also X-ray contrast media, which for example at the Computed Tomography (CT) may contain iodine. Despite this, there is an iodine deficiency in large parts of Central Europe. This mainly affects mountain areas, but also landlocked countries. The World health organization (WHO) estimates that around 750 million to one billion people worldwide live in one Iodine deficiency Suffer. With more than 380 million people affected, Western and Central Europe make a significant contribution to this. Because of this, iodine deficiency is the most common cause of one in Central Europe Enlargement of the thyroid gland. The highest concentration of iodine in the human organism is to be found in the thyroid gland, where iodine is in the Thyroid hormones Thyroxine (Tetraiodothyronine, T4) and Triiodothyronine (T3) is installed.
Because the body for it elemental iodine If necessary, the iodides taken in with food or medication are converted into elemental iodine. Iodide tablets are used for the prevention and treatment of thyroid diseases. Here, too, iodized salts are administered in the form of potassium iodide or sodium iodide. There is iodide as tablet or dragee with different strengths. Iodide preparations are pharmacy onlybut not subject to prescription. They should be taken with a sufficient amount of fluid after a meal.

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Iodine comes naturally in sea ​​fish and Seafood in front. Fish such as cod, golden bass and plaice are particularly good suppliers of the trace element iodine. Algae can also serve as a source of iodine. It is above all that Brown alga kelp which is a purely natural source of potassium iodide. If you don't like all of this, you can also eat other foods that contain iodine. Examples include dairy products, eggs and spinach. Another way of meeting the minimum requirement for iodine is to use iodized table salt. In addition, foods fortified with iodized salt can also help.

Pharmacokinetics and pharmacodynamics (mode of action)

As already described, iodine is almost exclusively found in food Form of its salts, that is, in the form of iodide contain. in the Gastrointestinal tract will this absorbed and gets into the so-called Extracellular fluid, the fluid that is present between the cells. Also the iodine, which is used when the iodine-containing Thyroid hormones is to be found in this room. Thus, the extracellular fluid serves as Iodide pool.
The iodide is then extracted from the extracellular fluid via a transport mechanism into a certain type of cell in the thyroid, the Follicular epithelial cell transported. In the cells, the iodide diffuses into the upper parts of the cell space, where it is transported across the cell membrane by transport proteins. As part of this, an enzyme called Thyroid peroxidase (TPO) for a chemical reaction, which ensures that the iodide is finally converted activated iodine arises.
After this reaction, the activated iodine can in certain Amino acid residues (Tyrosine residues) of Thyroglobulin (TG) to be built in. Thyroglobulin is a protein (protein) the thyroid gland, where the two thyroid hormones are produced. The intermediate product is created when an iodine atom is incorporated Monoiodotyrosine (mono = a), created by the incorporation of another iodine atom Diiodotyrosine (di = two).
Now comes the enzyme again Thyroid peroxidase (TPO) for use. This enzyme ensures that a diiodotyrosine is linked to another diiodotyrosine. This is how Thyroxine (Tetraiodothyronine, T4). On the other hand, if the enzyme combines a monoiodotyrosine with a diiodotyrosine, it is formed Triiodothyronine (T3). The two products thyroxine (tetraiodothyronine, T4) and triiodothyronine (T3) are the actual products Thyroid hormonesthat are bound to the protein Thyroglobulin (TG) im Thyroid follicle get saved. Thyroid follicles are closed compartments inside the thyroid gland.
When there is a need for thyroid hormones in the organism, these are first absorbed into the thyroid cells, where it is then used Dissolution of the thyroglobulin comes and thus also to release the tied to it Thyroid hormones. The thyroid hormones are ultimately stimulated by the Thyroid Stimulating Hormone (TSH), which comes from the anterior lobe of the Pituitary gland (Adenohypophysis) is released from the thyroid cells into the organism and can thus develop their effect.

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Effect of excess iodine on the synthesis of thyroid hormones

If the thyroid gland functions normally, a permanent Excess iodine (several hundred milligrams with an actual daily requirement of 200 micrograms) for one Inhibition of iodine uptake and the Thyroid hormone production. This effect is called Wolff-Chaikoff effect designated. This used to be done before a surgical treatment Overactive thyroid (Hyperthyroidism) with excessive release of thyroid hormones. One speaks of the so-called "Plopping“Because this therapy goes back to the American internist and endocrinologist Henry Stanley Plummer.
After a period of two to four weeks, the thyroid hormone synthesis is no longer inhibited by the excess iodine, so that the thyroid gland produces the hormones again despite the excess iodine. This effect is called Escape phenomenon and is no longer guaranteed in the event of thyroid disorders. For patients who have a chronic autoimmune thyroiditis (Hashimoto's thyroiditis), patients who have had their thyroid gland partially removed as part of an operation or those who have had a Radioiodine therapy have been treated, so a Excess iodine a Subfunction of the thyroid (Hypothyroidism) condition.

At a Thyroid enlargement because of a Iodine deficiency or due to thyroid nodules and hormone-releasing thyroid nodules (autonomous adenoma), on the other hand, iodine can be administered within weeks to months Hyperfunction (Hyperthyroidism) trigger.

Effect of iodine deficiency on the synthesis of thyroid hormones

With iodine deficiency, the Manufacturing the thyroid hormones for which iodine is required, limited. Due to the Feedback mechanisms is removed from the anterior lobe of the thyroid hormone deficiency Pituitary gland Thyroid stimulating hormone (TSH) with the aim of stimulating the growth of the thyroid gland (Hyperplasia) so that more thyroid hormones can be made.

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It is now known, however, that TSH is not the decisive factor for thyroid enlargement, but that thyroid growth is also triggered by local growth factors that are released from iodine-poor thyroid tissue. Thus, with iodine deficiency, the thyroid gland becomes enlarged (Iodine deficiency goiter) with initially still normal thyroid function (euthyroid goiter). However, if the iodine deficiency persists for a longer period of time, it can no longer be compensated by a healthy thyroid gland and iodine deficiency diseases develop.

Applications of iodide preparations

If the development of an enlargement of the thyroid gland is to be prevented, one is sufficient daily intake from 100 µg or 200 µg iodide. If the enlargement is already present, 200 µg to 400 µg are used daily to reduce the size of the thyroid. In contrast to children, it has been shown, especially in adolescents and adults with iodine deficiency goiter, that a Combination therapy With iodide and Thyroid hormones as opposed to pure iodide therapy. It was found that a dosage of thyroid hormone (Levothyroxine) and iodide in a ratio of 1: 2 (for example 75 µg levothyroxine plus 150 µg iodide) has the most effective effect on the regression of the enlarged thyroid gland.

In addition to iodide preparations that have to be taken daily, there are also preparations that are dosed in such a way that an intake once a week is sufficient. These products are especially for people who cannot guarantee a daily intake or for people with one increased iodine requirement suitable. If iodide is taken as a preventive measure, therapy is often necessary for years, not infrequently for a lifetime.If there is already an enlarged thyroid gland, therapy over a period of two to four weeks is usually sufficient for the regression of the thyroid gland in newborns. In children, adolescents and adults, longer treatment of 6-12 months, or even longer, is required.

Contraindications

Iodide is allowed in a manifest Hyperthyroidism (Hyperthyroidism) cannot be used. One speaks of manifest hyperthyroidism if the TSHValue in blood suppressed is, that is, under the Detection limit and the concentration of the thyroid hormones itself is increased. At a latent hyperthyroidism, i.e. if the TSH level is suppressed and the thyroid hormone concentration is still normal, a dose of 150 µg iodide per day must not be exceeded.
A dosage of 300 - 1000 µg iodide per day should not be exceeded if a benign, hormone-forming tumor (autonomous adenoma) or if it is known that areas of the thyroid gland produce thyroid hormones in an uncontrolled manner. This does not apply to treatment before a planned operation. Even with one Inflammation of the blood vessels (Urticarial vasculitis/hypocomplementemic vasculitis) and one Dermatitis herpetiformis Duhring, chronic skin inflammation should not be treated with iodide.
In the Hashimoto's thyroiditis, an autoimmune disease of the thyroid gland, larger amounts of iodine can aggravate the disease or, if predisposed, lead to a premature outbreak of the disease. Therefore iodine intake should be avoided if Hashimoto's thyroiditis is present. Even if close relatives at this one Autoimmune disease a differentiated approach is necessary. The iodine content in the daily food however, is not a cause for concern. Another autoimmune disease of the thyroid is Graves diseasewhere the uncontrolled production of thyroid hormones occurs. Even if this autoimmune disease is present, excessive iodine intake should be avoided as it can worsen the disease. Furthermore, hypersensitivity (allergy) against Potassium iodide or another component of the preparation from therapy with iodide.

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Be careful when taking iodine supplements

Before starting an iodine preparation, it should be examined whether an overactive thyroid gland (Hyperthyroidism) consists. This can be done with a simple blood draw.
It should also be checked whether there is a nodular goiter, since in individual cases an overactive thyroid can occur when iodine is taken.

If a hypersensitivity reaction to iodine is assumed, careful action is required. A hypersensitivity reaction to a food containing iodine or an X-ray contrast medium containing iodine in the past is usually not triggered by the iodine content, but by other components. However, if you had a reaction to a drug containing iodine in the form of an inflammation of the blood vessels (Urticarial vasculitis/hypocomplementemic vasculitis) or chronic skin inflammation (Dermatitis herpetiformis Duhring), iodine intake should be avoided, as high doses of iodine can worsen the underlying diseases.

For further important information on this topic, we recommend our page on: Iodine allergy - what to watch out for

Adverse drug effects

When taking iodide to prevent iodine deficiency goiter, no adverse drug side effects are to be expected in any age group. Even when treating an iodine deficiency goiter, children, adolescents and adults should normally not experience any side effects. In the presence of large, uncontrolled hormone-producing areas in the thyroid gland and a daily iodine intake of more than 150 µg, a manifestation of an overactive thyroid can rarely occur.
When taking 300 to a maximum of 1,000 µg per day for the treatment of enlarged thyroid in adults, iodine-related hyperthyroidism can occur in individual cases. This adverse drug reaction occurs primarily in elderly patients who have had an enlarged thyroid for a long time.

Hypersensitivity (allergy) to iodide can cause headache, fever, itching and burning of the eyes, dry cough, diarrhea and a rash. In this case, you should speak to the attending physician to stop taking the tablet.

Also read: Iodine allergy - what to watch out for

If you should experience an adverse drug reaction that has already been described, inform the attending physician so that he can decide how to proceed. You should also pass on adverse drug reactions that have not yet been described to the attending physician.

Interactions

Before you start taking iodide, your doctor or pharmacist should be informed about other medicines, including non-prescription medicines, that you are taking. During treatment of an overactive thyroid, iodine deficiency causes an increased response to drug therapy, whereas an iodine excess reduces the response to drug therapy. Because of this, the Hyperthyroidism any iodine administration should be avoided.

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Medication like Perchlorate or Thiocyanate (at a concentration of more than 5 mg / dl) inhibit the absorption of iodine into the thyroid gland. The simultaneous use of high doses of iodine, which inhibit the formation of hormones in the thyroid gland and lithium, for the therapy of psychiatric illness, can one underactive thyroid and promote the development of an enlarged thyroid. When taking potassium-sparing diuretics and potassium iodide can become a Increase in potassium levels come in the body.

pregnancy and breast feeding period

In the pregnancy should be both one Overdose of iodine, as well as an iodine deficiency, as both are damage of the unborn child. However, a pregnant woman does have one increased need of iodine, so that a sufficient supply of iodine is important during this time. When taking iodine supplements with a dosage of up to 200 µg daily no damage to the unborn child has yet been described. However, higher dosages should only be used if there is a manifest iodine deficiency, since the iodine can penetrate to the unborn child and to a Goiter formation and an underactive thyroid gland in the womb. In addition to pregnancy, there is also an increased need for this during breastfeeding Trace element iodine.

Even during this time, iodine preparations with a dosage of 200 µg can be administered daily. Higher dosages should be avoided if there is no iodine deficiency, as iodine has the ability to absorb Breast milk to reach and enrich yourself here. In general, iodine preparations should only be taken during pregnancy and breastfeeding if specifically prescribed by a doctor. If you are unsure, you should definitely consult your doctor or pharmacist.


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