Iodine: essential and much-debated trace element

Figure 1: Iodine is an essential mineral that fulfils numerous functions in the body. Among other things, this trace element is indispensable for the production of thyroid hormones.

Few trace elements are discussed as frequently and controversially as iodine. While some demonise iodine as a toxin, others emphasise the importance of adequate intake and advocate iodine supplementation. In this blog post we would like to present this essential trace element as clearly and objectively as possible. Among other things, you will learn which vital tasks iodine performs in the body, which different types of iodine exist and why pregnant and breastfeeding women should pay particular attention to their iodine supply. You will also find information on the status of iodine intake in Germany as well as the pros and cons of iodine supplementation.

Iodine: an essential mineral with many facets 

Like iron, zinc or selenium, iodine is an essential trace element and therefore vital. As such, it cannot be synthesised by the human body and can only be stored to a limited extent. It is therefore crucial to obtain iodine regularly from the diet. Iodine is primarily known for contributing to the regulation of metabolism and supporting normal thyroid function. Seventy to eighty per cent of the iodine available in the body is stored in the thyroid. The trace element is also found in small amounts in blood plasma and in the lungs and kidneys and — during pregnancy and breastfeeding — in the mammary gland.

The central functions of iodine in the human body

Figure 2: As an important building block for the formation of thyroid hormones, iodine influences numerous bodily areas and processes, including energy metabolism and the nervous and immune systems.

Iodine is of great importance for our health and vitality. The mineral plays a key role in numerous metabolic processes and is particularly important for our nervous system. Below we briefly present some of the central functions and mechanisms of action of this trace element.

Thyroid function

The thyroid is not only the main storage site for iodine in the body but also the organ in which up to 80% of the daily absorbed iodine is used. When iodine is taken in through the diet, it first passes from the gastrointestinal tract into the blood and from there is largely transported to the thyroid. The mineral is urgently needed here for the formation of thyroid hormones. If insufficient iodine is available, the important hormones thyroxine (T4) and triiodothyronine (T3) cannot be produced in adequate amounts.[1] T4 and T3 influence numerous bodily processes, including blood pressure, tissue growth and the basal metabolic rate (the body's energy requirement at rest).

Long-term iodine deficiency of the thyroid can lead to hypothyroidism and other health problems. However, excess iodine can also have negative effects on the thyroid (see the section “How dangerous is an iodine excess?”). To ensure normal thyroid function, it is therefore sensible to check your iodine status regularly by measurements in blood or urine.

Cognitive performance

We can benefit from adequate iodine intake at all stages of life. The thyroid hormones T4 and T3, the formation of which requires iodine, regulate neuronal differentiation and synapse formation. By regulating the production of neurotransmitters such as dopamine and serotonin, thyroid hormones — and thereby indirectly iodine — play a crucial role in regulating the nervous system. They also promote glucose metabolism in the brain, which is essential for optimal cognitive function. Iodine is not only critical for neural development in infancy and childhood. Adolescents, adults and older people also need this mineral to maintain cognitive performance. Even a mild iodine deficiency often leads to concentration difficulties and reduced attention, while a moderate to severe deficiency in children can cause delayed language and learning abilities.

Energy metabolism and the nervous system

The thyroid is one of the organs in our body that most strongly regulates metabolic processes. Thyroid hormones control not only the basal metabolic rate but also thermogenesis (heat production) and fat and carbohydrate metabolism. In addition, T3, the active form of the thyroid hormone, stimulates the mitochondria in our cells. This enables increased ATP (adenosine triphosphate) production overall, which serves as an energy source for the body. In addition to the metabolic processes already mentioned, iodine is also involved in protein synthesis. Proteins fulfil a variety of functions in the body. Among other things, proteins are important for tissue growth, immune defence, energy supply and cell division.

Support of the immune system

Can iodine strengthen the body's own defences? Yes — it can! Among other things, the mineral indirectly ensures via thyroid hormones that so-called T and B cells can mature. T cells are crucial for the cellular immune response, while B cells produce important antibodies that can recognise and neutralise pathogens such as bacteria, viruses and fungi. But even independent of its action via thyroid hormones, iodine possesses properties that can positively influence the immune system. For example, the mineral has a disinfectant effect and is therefore a common component of antiseptic solutions.

Moreover, iodine is involved in the formation of reactive oxygen species (so-called ROS), which can help the body defend against pathogens. For iodine to have positive effects in the area of immune defence, however, adequate dosing (neither too much nor too little iodine) must be ensured (see also the section “Iodine requirements: How much iodine do we need daily?”). In the case of an iodine excess, immune system overstimulation can occur, leading to misdirected immune responses and inflammation.

The different forms of iodine and their properties at a glance

In nature and medicine, iodine occurs in different forms and compounds, each with different properties and suitability for certain applications. The table below provides an overview and a short description of the most relevant forms of iodine.

Which natural foods are particularly rich in iodine?

Figure 3: The highest iodine concentrations are found in animal foods such as sea fish or seafood. But some plant foods also contain the trace element in significant amounts.

In nature iodine is found mainly in the oceans, while soils are comparatively iodine-poor. It is therefore no surprise that foods such as seaweed and seafood are particularly rich in iodine, whereas plant foods usually contain the trace element in much smaller amounts. Animal foods such as milk, eggs and cheese can also contribute to covering iodine requirements, as iodine is often added to animal feed.

The following foods are good natural sources of iodine:

• Seaweeds (e.g. kombu, wakame, nori)
• Fish (e.g. cod, salmon, tuna, herring)
• Seafood (e.g. mussels, crab)
• Eggs
• Dairy products (e.g. yoghurt, cheese)
• Potatoes

People who follow vegetarian or vegan diets are often advised to use iodised table salt to optimise their iodine intake.[2] It should be noted, however, that iodine can evaporate during cooking or be discarded with cooking water. Iodine in iodised salt also gradually dissipates over longer storage periods and if stored open, which is why iodised table salt is not a particularly reliable iodine source. A good and nutrient-rich alternative to iodised salt is dried algae flakes such as the Bio Dulse flakes from Unimedica. The salty flakes, raw-food quality, enrich many dishes with their red colour and unique flavour.

It is also important to know that some foods, such as sweet potatoes, soybeans or brassica vegetables, can inhibit iodine absorption.[3] Certain constituents bind iodine from the diet and thus reduce its bioavailability. However, this is only likely to be relevant with very high consumption of the mentioned foods.

Why is iodine intake so important during pregnancy?

Adequate iodine intake is one of the many things expectant mothers should pay attention to. During pregnancy, two thyroids (the mother's and the unborn child's) need to be supplied with iodine so that enough thyroid hormones can be produced for both. This results in an increased iodine requirement for the mother during pregnancy, which according to the German Nutrition Society (DGE) is around 200 to 230 micrograms of iodine per day. Breastfeeding women are generally recommended an even higher iodine intake of 200 to 260 micrograms per day.

Because iodine is crucial for the embryo's growth and the development of the nervous system, iodine deficiency during pregnancy can have serious consequences. Among other things, it can lead to cretinism, a severe mental and physical developmental disorder caused by iodine deficiency during pregnancy. Slowed physical growth and delayed development in children are also possible.

A prospective observational study from the UK impressively illustrated the possible effects of iodine deficiency in pregnant mothers.[4] In the study, the median urinary iodine concentration of 1,040 pregnant women was measured. At the ages of 8 and 9 years, the children of the study participants took an intelligence and a reading test. It was found that the children of women who were not adequately supplied with iodine during pregnancy were 58% more likely to fall into the quarter of children with the lowest verbal IQ. In the reading tests, children of iodine-deficient mothers performed 69% worse. As this was an observational study, a causal link between maternal iodine deficiency and lower child IQ could not be unequivocally proven. Further large-scale clinical studies to investigate a possible causality are desirable.

What are iodine tablets and what are they used for?

You may also have heard of iodine tablets and wondered what exactly they are. Of course there are also dietary supplements in tablet form that contain iodine and are designed as complementary iodine sources. However, the term “iodine tablets” generally refers to special, very highly dosed tablets intended exclusively for emergency situations. Since radioactive iodine can cause aggressive thyroid cancer, iodine tablets are often distributed to the population in nuclear disasters. If taken ideally once 24 to 48 hours before contact with a radioactive iodine cloud, they can initiate a so-called iodine blockade. The very high dose of about 50 milligrams of iodine per tablet then ensures that the thyroid is already so saturated at the time of contact with radioactive iodine that it can no longer absorb it and is therefore protected from damage.

The status of iodine intake in Germany

Germany was long classified as an iodine-deficient area, which has mainly geological and geographical causes: during the last ice age, soils and rocks in Central Europe were heavily leached by meltwater. As iodine is water-soluble, much of it was washed into the sea and lost. For this reason, soils in Germany and the plants grown on them remain comparatively low in iodine to this day. Groundwater in this country also contains little iodine. To counteract the resulting significant iodine deficiency, targeted measures were taken in the 1980s. In addition to information campaigns, the introduction of iodised table salt and the enrichment of animal feed with iodine were important components of so-called iodine deficiency prophylaxis in Germany and other European countries.

However, iodine deficiency is a widespread global problem. According to the WHO, about one third of the world's population is inadequately supplied with iodine; in Europe it is estimated to be as much as half of the population.[5] The Robert Koch Institute has also published alarming figures showing that average iodine intake in Germany is currently declining again. According to the RKI, as many as 32% of German adults have an increased risk of iodine deficiency.[6] Among children and adolescents, almost 44% are estimated not to meet their median iodine requirement.[7]

Iodine requirements: How much iodine do we need daily?

The question of how much iodine should be consumed daily cannot be answered uniformly. Individual iodine requirements depend on various factors such as age, diet and any pre-existing conditions. Daily requirements also change in special life stages such as pregnancy or breastfeeding. In addition to iodine intake, the supply of other trace elements such as selenium, zinc and iron should always be monitored, as deficiencies of these substances can impair iodine utilisation.

The German Nutrition Society (DGE) recommends the following daily iodine intake in Germany for different age and population groups:[8]

Which symptoms indicate iodine deficiency?

Figure 4: A typical symptom of iodine deficiency is enlargement of the thyroid, visible at the neck as a goitre (medical term: struma).

If iodine intake is temporarily inadequate, this is usually not a major concern, as the body can store small reserves of the mineral in the thyroid and draw on them when needed. However, if insufficient iodine is consumed over a longer period, iodine deficiency can develop, typically accompanied by the following symptoms:

• Tiredness and exhaustion
• Concentration problems
• Depression or mood swings
• Muscle weakness
• Pale and dry skin
• Hair loss
• Increased susceptibility to infections
• Weight gain

If iodine deficiency persists over a longer period, it can become chronic. The thyroid attempts to compensate and continue producing sufficient thyroid hormones. To maximise iodine uptake, thyroid tissue enlarges and a swelling appears in the neck area, known as a goitre (struma). This goitre formation is not only cosmetically bothersome in many cases, but can also cause health problems such as difficulty swallowing or shortness of breath.

How dangerous is an iodine excess?

Given the widespread iodine deficiency, iodine excess is generally considered less problematic. In addition, if the thyroid is functioning normally it automatically ensures that excess iodine is excreted via the kidneys. It is also unlikely that worrying amounts of iodine would be consumed through diet alone. The risk of overdose arises mainly when consuming large quantities of seaweed products, highly dosed iodine supplements or iodine-containing medicines. Both over- and under-stimulation of the thyroid can result from iodine over-supply. One possible consequence of excessive iodine intake is hyperthyroidism, which is often accompanied by a rapid heartbeat, nervousness and hot flushes.

Excessive iodine intake can also block hormone production and lead to iodine-induced hypothyroidism. Other possible symptoms of iodine excess include iodine acne, skin rashes, allergic reactions (iodine allergy) or a painful inflammation of the thyroid (iodine-induced thyroiditis). To prevent iodine excess, the German Federal Institute for Risk Assessment (BfR) recommends a maximum daily iodine intake of 500 micrograms (µg) from all sources for adults, including food, dietary supplements and table salt.[9]

The pros and cons of iodine supplementation

If you are considering taking iodine as a dietary supplement, you should weigh up the pros and cons carefully. One of the main reasons many people opt for iodine supplements such as iodine capsules or iodine drops is the simplicity of dosing. While iodine intake from food can only be estimated, supplements allow precise, needs-based dosing. In addition, use is generally very straightforward, which is why iodine products are often a sensible option to prevent or treat iodine deficiency.

However, iodine supplementation can also have negative effects, especially if the tolerable intake is exceeded. If too much iodine is taken, which the body cannot process, there is a risk of iodine excess, with the negative consequences described in the previous section. To ensure safe iodine supplementation, you should therefore determine your individual requirement beforehand. If you are taking high doses of iodine, continuous medical consultation and monitoring during the supplementation period are also important.

Who should not supplement with iodine?

Certain groups of people should be particularly cautious about iodine supplementation or should ideally avoid it altogether. These include especially:

• People with thyroid diseases such as Hashimoto's thyroiditis or Graves' disease
• People with hyper- or hypothyroidism
• People with iodine intolerance or allergy
• People with renal insufficiency
• Elderly people with autonomous thyroid adenomas (thyroid nodules)

In autoimmune thyroid diseases such as Hashimoto's thyroiditis, high iodine intake can exacerbate thyroid inflammation and worsen the symptoms of hyper- or hypothyroidism.

Tips and advice for choosing an iodine product

If you want to use iodine as a supplement, you can choose from a wide range of iodine products. Classics among iodine-containing supplements include capsules such as the Bio Iodine capsules from Unimedica. Each capsule contains 150 µg of iodine, which corresponds to the recommended daily dose for healthy adults. Before purchasing iodine capsules, always check the origin and quality of the product you have selected. The natural iodine contained in the iodine capsules from Unimedica comes from Icelandic organic kelp extract. The capsules are manufactured in Germany.

Another very popular form of iodine supplementation is iodine drops. As in the iodine drops from Unimedica, most liquid preparations contain elemental iodine. Iodine drops can usually be simply added to a glass of water and drunk. If you are looking for a product for external use, Lugol's solution may be exactly what you want. Named after the French physician Guillaume Lugol, this iodine solution has been used for wound cleaning and as a home remedy since the 19th century. The Lugol's solution from Unimedica is produced according to the original 1835 recipe and conforms to the European Pharmacopoeia (Note: for external use only and not suitable for ingestion!).

There are now numerous nutrient complexes that contain iodine for targeted strengthening of specific organs or support in certain life phases. For example, the Skin Vitamins from Unimedica contain a rounded nutrient complex that, in addition to iodine, includes substances such as biotin, riboflavin, niacin and zinc, which contribute to the maintenance of normal skin. The Thyroid* Complex from Unimedica is a harmoniously balanced premium complex whose ingredients were selected for their specific roles in supporting thyroid function. In the vegan Woman 40* Complex from Unimedica, iodine, coenzyme Q10, hyaluronic acid and OPC play the main roles. The carefully considered nutrient combination was specially developed for the needs of women aged 40 and over.

How to use iodine supplements correctly

How best to take iodine products depends primarily on the dosage form and the intended use, but also on your personal preferences. Always consult a doctor before you start taking an iodine product. Your doctor can recommend a suitable regimen that avoids overdosing or side effects from iodine supplementation.

Iodine capsules should normally be taken once daily with sufficient liquid. The time of day generally does not matter. However, if you find that taking iodine in the evening affects your sleep, it may be sensible to choose an earlier time. Especially at higher doses, taking iodine on an empty stomach can cause discomfort and nausea. People who are sensitive to iodine-containing supplements should therefore take iodine capsules or iodine drops with or after a meal to improve tolerability.

It is also important to be aware of possible interactions with other supplements and medications when supplementing with iodine. These are rare but can have significant negative consequences. For example, iodine can affect the efficacy of thyroid hormones such as L-thyroxine, which is why a gap of several hours should always be observed between iodine and hormone intake. The same applies to iron and calcium supplements, as these can reduce iodine absorption in the gut. People taking medication for cardiac arrhythmias or ACE inhibitors should also seek medical advice before taking iodine.

Biography

Katharina Korbach regularly writes blog posts on medicinal plants and natural active ingredients for Narayana Verlag. She developed an early interest in language and began writing her own literary texts. A serious illness during her final school year prompted an intensive engagement with health and nutrition topics that continues to this day. After repeated failures of conventional medical treatments, she opted for a more self-empowering, naturopathic therapeutic approach. A plant-based diet was a key element in her path to recovery.

Katharina studied Cultural Studies (B.A.) and Applied Literary Studies (M.A.). In 2022 she published her debut novel “Sperling” with Berlin Verlag. Today she lives in Berlin as a freelance author, medical editor and lecturer. In her free time she prefers to spend time with friends or at barre training. She also loves travelling and trying out new vegan recipes.

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[5] WHO (World Health Organization): Iodine status worldwide: WHO global database on iodine deficiency. Geneva 2004. https://iris.who.int/bitstream/handle/10665/43010/9241592001.pdf (accessed: 02.01.2025).

[6] Remer T, Thamm M. Final report: Determination of daily iodine and salt intake of adults in Germany: Biomarker-based data analysis of the representative DEGS study and methodological basis for future health surveys. 2015.

[7] Hey I, Thamm M. Final report: Monitoring iodine and sodium intake in children and adolescents within the Robert Koch Institute study on the health of children and adolescents in Germany (KiGGS Wave 2). 2019.

[8] DGE (2000): Reference value for iodine. https://www.dge.de/wissenschaft/referenzwerte/jod/ (accessed: 02.01.2025).

[9] BfR (2021): Maximum amount recommendations for iodine in foods including dietary supplements. https://www.bfr.bund.de/cm/343/hoechstmengenvorschlaege-fuer-jod-in-lebensmitteln-inklusive-nahrungsergaenzungsmitteln.pdf (accessed: 04.01.2025).

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