As with numerous other nutrients, there are numerous myths and pseudo-scientific statements about the essential micro-mineral iodine, which unfortunately often contribute to cognitive distortions and misunderstandings in public perception.
Especially in the context of the thyroid, contradictory statements are often made in this regard.
On the one hand, the essential health properties of the micronutrient are pointed out, but on the other hand, a warning is given against excessive intake.
In this context, warnings are often given against regular and excessive consumption of algae, as they sometimes have an above-average iodine content and are associated with correspondingly negative effects on thyroid functionality.
Is iodine a legitimate risk for the thyroid or is it the result of generalization with a lack of differentiated perspective?
In this article, we strictly distinguish populist, twisted statements from the concrete scientific facts and core tasks of the micronutrient iodine and take a deeper look at the topic of " algae ".
For those who want a quick answer to the question in the title of the article, this is:
Iodine is a double-edged sword that should be taken very defensively depending on the individual supply of your own thyroid gland. In principle, however, the iodine content of the freshwater algae Chlorella is so low that it plays no relevant role in this context.
For those who want a detailed answer and a deeper understanding of this topic, here is the article:
Iodine - An Introduction
The term " jod " originally comes from the French word " iode ", which in turn was derived from the Greek " ἰοειδής ".
This name was first proposed by the French physicist and chemist JP Gay-Lussac because of the characteristic purple color in the gaseous state.
Nowadays, iodine belongs to the category of essential nutrients. The human organism is therefore not able to produce iodine independently, which is why one is dependent on a basic alimentary supply.
In detail, iodine is assigned to the group of so-called micro-minerals or trace elements and is only present in the organism in relatively small absolute amounts.
Only about 0.000016% of the human body is made up of iodine. Nevertheless, the trace element has a broad and multidirectional range of tasks.
It is essential for normal or optimal thyroid function, acts as an important core nutrient for growth, metabolism, reproduction, regulation of body temperature, nerve and muscle function, and human blood cell production.
For a long time it was assumed that the thyroid cells (thyrocytes) are the only cells in the human body that can actually absorb the valuable iodine.
While a high specificity of the micronutrient to the thyroid is correct, additional physiological functions have emerged over the past two decades.
In particular, iodine is said to have strong antioxidative and radical-scavenging activities, so that it takes on important tasks in the body's immune system.
Experts therefore call iodine " one of the oldest antioxidants in living organisms ".
In addition, it has recently been shown that iodine oxidation to hypoiodite (IO-) in the salivary glands, stomach and intestine has potent bactericidal, antiviral and antifungal properties.
In specialist literature on the subject of " iodine ", the trace element is also often classified or synonymized as halogen. This is based on the fact that iodine together with fluorine, chlorine, bromine and astatine form the elements of the seventh main group of the chemical periodic table.
Elementary iodine is not found in nature in its free form, but primarily in mineral form as iodide or iodate.
Most of the iodide is found in the oceans. In the natural regulatory cycle of the trace element, iodine is first released from the seawater into the atmosphere through oxidation and from there it is finally returned to the soil and groundwater through rainfall.
However, this cycle is subject to strong regional fluctuations, which is why many soils, including the plants grown on them, have a low iodine content today.
The areas with endemic iodine deficiency include, for example, the European mountain regions, the Ganges Valley in India and the Andes region in South America.
Many algae, on the other hand, have a very high iodine content because, unlike agriculturally grown plants, they can absorb the halogen directly from the oceans.
Iodine and its Health Claims
The value of the trace element for the human metabolism is also reflected in the approved health claims:
- Iodine contributes to normal production of thyroid hormones and normal thyroid function
- Iodine contributes to normal cognitive function
- Iodine contributes to normal energy metabolism
- Iodine contributes to the normal functioning of the nervous system
- Iodine helps maintain normal skin
- Iodine contributes to the normal growth of children
These functions, which are approved in the EU and are therefore scientifically very clearly proven, indicate which important functions iodine has in our body and how important iodine is for us.
Which leads directly to a next question: How much iodine should we take?
The recommended daily dose of iodine
According to the German Society for Nutrition, the recommended daily iodine intake for an adult in Germany is 180 to 200 µg (micrograms).
For pregnant and breastfeeding women, the recommendation is 230 to 260 µg due to the increased requirement.
These are the general recommendation that we should primarily cover from our diet.
Which leads directly to the next question: Where is iodine found in our food?
iodine from food
The natural sources of iodine that contribute to the supply of the micronutrient include meat, eggs, dairy products, sea shellfish and algae.
Analyzes of preschool children from Germany showed, for example, that cow's milk, salt and eggs are currently the most important sources of iodine supply.
Individual eating habits as well as regional and cultural differences have a corresponding influence on a person's individual iodine supply.
The current iodine supply situation
Although the importance of the trace element in human physiology has been known for over 100 years, an adequate iodine supply is still not considered to be guaranteed, both in Germany and at the global population level.
It is estimated that around 2 billion people worldwide continue to be affected by iodine deficiency.
Leading experts as well as national and international organizations (WHO, ICCIDD, IGN) regard the regular consumption of iodised table salt in daily kitchen use as one of the best preventive measures to prevent iodine deficiency.
A recommendation that is actually implemented by less than 35% of the population in Germany.
A potential reason why Germany is still classified as an iodine deficiency region today.
Is iodized salt enough to remedy this deficiency?
Iodized salt contains about 32 mg potassium iodate per kilogram, which corresponds to 20 mg iodine. By using just 5 g of iodized salt per day, you can supply the organism with 100 μg of additional iodine in an uncomplicated way.
In some cases, however, well-meaning experts explicitly advise against using iodized table salt.
From medical considerations in terms of optimal cognitive and physical development as well as performance, these recommendations against iodized salt do not appear to be rationally justified.
A need-based use of iodized salt in the kitchen does not lead to excessive hormone production or to other thyroid-specific metabolic imbalances.
In addition to iodized salt, there is of course also the option of other iodine-containing foods such as lower seaweed to cover the iodine requirement.
According to the specific opinion of the German Society for Endocrinology, table salt-based iodine supplementation does not cause any symptoms in a physiologically working thyroid gland.
The focus of this statement should certainly be on "a physiologically working thyroid gland". The fact that there can be individual differences here is an important point, the need-based intake of iodine.
How can I determine my iodine needs?
The urinary iodine excretion is the most important laboratory test to determine an adequate iodine supply.
However, this test procedure sometimes has severe limitations.
The iodine excretion in the urine is influenced, among other things, by the individual fluid intake or previous consumption of iodine-containing foods, which is why the values obtained and the measurement result can be more or less strongly falsified.
In addition, the 24-hour urine collection is usually not used in everyday clinical practice, but only spontaneous urine, which is even more susceptible to fluctuations in terms of iodine concentration.
Significantly more valid results, on the other hand, can be achieved using iodine measurements in the blood. Unfortunately, this method is not yet part of the clinical medical standard.
Thus, as with many other micronutrients, the laboratory analysis of the individual need for iodine has its limitations in practice.
One way to determine individual needs is to combine the laboratory test with the change in subjective perception of performance and well-being and other objective tests such as the YPSI skinfold measurement .
Based on this, it may make sense to supplement with iodine in addition to the intake of iodine from food.
Due to its essential functions, especially in terms of physical and mental development, supplementation is nowadays particularly recommended for pregnant and breastfeeding women.
As already mentioned, these have a statistically higher iodine requirement.
If supplementation takes place, the compounds potassium iodide, potassium iodate and calcium iodate are primarily used.
In the case of an iodate supply (e.g. via iodised table salt), this is converted to iodide in the intestine via reduction, then absorbed and processed accordingly.
If an adequate iodine supply is not ensured during embryonic and fetal development as well as postnatal, this can lead to severe and delayed physical and mental development, which in the worst case manifests itself in the form of cretinism.
In 1990 it was estimated that overt cretinism affected approximately 11.2 million people worldwide. A further 43 million people are said to be affected to a lesser extent by mental impairments induced by iodine deficiency.
Experts even assume that thyroid hormone production, which is impaired both during pregnancy and in child development, can lead to a compromised intelligence quotient due to a lack of iodine supply.
Specifically, this can contribute to a loss of up to 15 IQ points.
Which impressively indicates the influence of iodine on the thyroid gland.
Iodine and the Thyroid
Probably the most popular task of iodine is its function in the human thyroid metabolism.
There is no alternative to the halogen for the synthesis of thyroid hormones and thus for optimal thyroid functionality and metabolic regulation.
This is based on the fact that iodine is essential to the process known as iodization.
In the gastrointestinal tract, dietary iodine (more precisely iodide) is first absorbed into the bloodstream and then transported to the thyroid gland.
More than 90% is absorbed in the duodenum.
The uptake into the thyrocytes takes place together with sodium primarily via so-called sodium iodide symporters. The iodization process follows intrathyroidally. In this process, iodine is attached to the protein thyroglobulin, which is also synthesized in the thyroid cells, with the help of hydrogen peroxide.
In simple terms: iodine and tyrosine are linked together.
The thyroid hormones T3 and T4, which are so important for the human metabolism, then arise from this process.
Iodine thus functions as an essential structural component of these hormones, both in the active T3 (TriJodThyronine) and in the metabolically inactive T4 (Thyroxine).
A crucial aspect that often gets too little attention is the fact that thyroglobulin is a tyrosine-rich protein.
This creates a direct link between the importance of regular, rotational and sufficient protein consumption and optimal thyroid function.
Protein is a crucial nutritional regulator for our thyroid gland and a lack of tyrosine supply is associated with restricted thyroglobulin synthesis and thus compromised thyroid performance.
Last but not least, this is one of the reasons why we advise customers and athletes with whom we work to adopt a generally high-protein diet.
Red meat is the best source of tyrosine.
So a lack of protein goes hand in hand with an iodine deficiency.
Iodine deficiency and the formation of a goiter
Iodine deficiency is associated with increased goiter formation.
Goiter formation due to increased tissue growth is mostly to be understood as a biologically compensatory and adaptive reaction of the thyroid gland.
Through growth (hyperplasia), the thyroid tries to compensate for an iodine deficiency and continue to ensure the production of physiologically required amounts of hormones.
T4 and T3 continue to be produced via the newly synthesized tissue, but are physiologically decoupled from the thyrotropic control circuit and are therefore functionally autonomous or uncontrolled.
Two indirect laboratory tests for iodine
The reduced hormone production (T3, T4) due to the previous chronically inadequate iodine supply leads to an increase in TSH in the negative feedback loop of the thyroid gland.
Initially increased T3 values can also indicate an iodine deficiency.
In this case, the body tries to compensate for the lack of iodine intake through a compensatory increase in the synthesis of triiodothyronine, since this has a significantly lower iodine content and is more metabolically active than thyroxine.
T3 has 5-8 times the metabolic potency of T4 and requires only about 75% as much iodine for synthesis.
Thus, the increase in the T3/T4 quotient can also be viewed as an indicator of a gradual iodine depletion of the thyroid gland.
T3 and the T3/T4 quotient are part of a comprehensive laboratory test of the thyroid hormones, which also determines T4, T3 and rT3 in addition to TSH.
Be careful when starting iodine supplementation!
Scientific studies show the tendency that an improved iodine supply in regions where an iodine deficiency previously prevailed for a long time could reduce the incidence of goiter formation, but at the same time promoted the occurrence of thyroid-specific autoimmune diseases and inflammation.
According to the experts, the transition phase between an inadequate and an optimal iodine supply situation is particularly decisive.
Normally, iodine levels of 1000 to 2000 μg per day can be tolerated by a healthy thyroid without complications.
However, this tolerance limit is significantly lower for populations that have been exposed to iodine deficiency in the past.
In other words, these people are much more sensitive and susceptible to a sudden increase in iodine intake.
If patients with already developed nodules, caused by an iodine deficiency, suddenly consume excessive amounts of the halogen, the hormone production is initially normalized.
The " healthy " tissue begins to synthesize normal amounts of T4 and T3.
However, the compensatory formed and autonomously working tissue (nodes & goiter) produces additional amounts of hormones and can even be additionally activated by the increased iodine supply.
This combination quickly produces above-average amounts of T4 and T3, which promotes the development of iodine-induced latent hyperthyroidism.
Based on these biochemical relationships, it also explains why various bodies around the world have set different upper limits for the trace element.
The retrospective consideration of the iodine supply situation and the prevalence of iodine-induced clinical complications of the thyroid gland in the specific population of a country are considered decisive.
Due to their history, some populations are simply constitutionally more robust to higher iodine exposure.
Is there iodine poisoning?
Under normal circumstances, acute iodine poisoning based on purely nutritional intake is very difficult.
In principle, gram-by-gram supplies of the trace element are necessary.
The symptoms include classic poisoning symptoms such as fever, abdominal pain, vomiting or diarrhea.
One of the most common causes of excessive iodine exposure is the application of iodine-containing pharmaceuticals such as the antiarrhythmic amiodarone, which is used to treat cardiac arrhythmia.
A similar danger exists in the use of iodinated X-ray contrast media in imaging procedures, which serve the purpose of improving the representation of body structures.
Furthermore, an excess of iodine can also be caused by the incorrect use of (highly dosed) food supplements or the too regular consumption of foods high in iodine, such as seaweed, which in turn evokes the pathogenesis of various thyroid-specific dysfunctions.
These clinical pictures, documented by case reports, include, for example, the Wolff-Chaikoff effect (acute blockade of iodine uptake), the development of autoimmune diseases (Graves' disease, Hashimoto's disease) or the development of over- or under-function and inflammation of the thyroid gland.
Autoimmune diseases of the thyroid
Diseases of the thyroid gland primarily include underfunctioning and overfunctioning in different genesis and severity as well as immunological malfunctions, which manifest themselves in the form of an autoimmune disease.
An autoimmune reaction is ultimately to be understood as a malfunction or incorrect reaction of the immune system.
In this case, the immune system attacks the body's own cells and turns against its own organism, so to speak.
In the context of the thyroid, experts sometimes assume that about 90% of the dysfunctions that evolve are autoimmune-based.
The well-known and most frequently occurring thyroid-specific autoimmune diseases include Graves' disease (immune thyroid disease) and Hashimoto's disease (autoimmune thyroiditis).
Graves' disease is characterized by the development of specific TSH receptor antibodies, which subsequently permanently occupy and stimulate the TSH receptor.
The thyroid therefore constantly receives the signal to produce “ more hormones ” and is subject to permanent activation, which inevitably leads to overfunctioning.
The thyroid stimulating hormone (TSH) is a pituitary hormone (pituitary gland) which basically stimulates the thyroid gland to synthesize, store and release thyroid hormones.
It also has a decisive influence on the control of intrathyroid iodine uptake.
In clinical practice, TSH is often propagated as the most important parameter for assessing the thyroid-hormone axis.
It is subject to so-called negative feedback loops, so that elevated TSH values can indicate hypofunction (hypothyroidism) and a suppressed TSH value is interpreted analogously as a typical sign of hyperfunction (hyperthyroidism).
Ideally, the TSH value should be < 2, but a TSH concentration of > 3 μU/ml is considered hypothyroidism.
But be careful, the hormone is just one building block in a whole range of different potential influencing factors and, viewed in isolation, only provides an incomplete picture.
Determining the TSH value alone is therefore not sufficient to obtain a comprehensive diagnostic insight into the current thyroid functionality of a person.
In order to be able to better assess the complex and multi-causal relationships of the thyroid gland, it is particularly recommended in practice to also determine the fT3, fT4 and rT3 values in the blood count.
In contrast to Graves' disease, Hashimoto's disease is not directed against the thyroid-specific receptors but against the organ itself.
In this autoimmune reaction and immunologically caused thyroid inflammation, the body's own thyroid tissue is actually destroyed.
This process finally evokes a restricted or even completely declining production of hormones by the thyroid gland, so that the supraphysiological state of hypothyroidism manifests itself.
As a therapeutic concomitant, in many cases a patient is dependent on lifelong drug T4 substitution.
Since Hashimoto's disease has a much higher prevalence in society than Graves' disease, this autoimmune disease is considered one of the main causes, which is why thyroxine preparations are among the most frequently prescribed drugs worldwide.
Where is the connection between algae and iodine?
Due to their high iodine content, (dried) seaweed was again classified as an unsafe food by the Federal Institute for Risk Assessment (BfR) in 2012, with the result that the topic of " algae " repeatedly became the focus of sometimes populist discussions.
Since iodine always accumulates in seawater and is then stored by the native algae, specially dried seaweed products have a particularly high iodine content.
Even small portions consumed by the gram (10g) can contain up to ten times more iodine than the upper iodine intake limit of 0.5 milligrams (500 µg) per day that is classified as safe in Germany.
The daily recommended maximum iodine intake can thus be quickly exceeded.
In individual cases, certain seaweed products were even withdrawn from the market and publicly recalled due to their above-average iodine content, including a lack of warnings and consumption recommendations, since damage to health could not be ruled out.
For example, the Chemical and Veterinary Investigation Office (CVUA) in Stuttgart reports that a " high iodine content in algae products can be dangerous ".
According to the recommendation of the BfR, dried algae products with an iodine content of 20 milligrams per kilogram should even be classified as " not marketable ".
Seaweed vs. Freshwater Algae - A Differentiation
Admittedly, based on these analyses, one easily runs the risk of making a hasty judgment about algae and classifying them as fundamentally harmful to health.
Unfortunately, such generalized statements are often made today in articles and publications on this topic on the Internet.
However, there are no more precise differentiations between algae-specific intra-individual differences in terms of iodine content.
As a consequence, reductionistic and sometimes twisted facts quickly arise, so that seaweed is suddenly equated with freshwater algae and the very valuable chlorella, for example, is said to have negative effects on the thyroid function from now on.
A more in-depth approach is therefore necessary.
In principle, it must be taken into account that the individual iodine content is subject to considerable fluctuations depending on the type of algae examined and the region of origin.
Some studies found differences of 5 and 11,000 milligrams per kilogram of dry weight.
In contrast to seaweed, freshwater algae contain significantly less iodine.
Laboratory analyzes of selected chlorella products show that 100 g of chlorella contain between 20 mg and 70 mg iodine.
Compared to seaweed, which sometimes contains 5,000 mg iodine and more per 100 g.
Comparative iodine content measurements between sea and freshwater fish also confirm the evaluated tendencies.
Biological samples in the fillet of the fish showed a 5 to 10 times higher iodine concentration in saltwater fish than in freshwater fish species.
If the health risk potential of some algae products can be classified as high depending on the dose and sensitivity of a person, this does not apply to the chlorella algae native to freshwater.
Iodine - A Summary
The subject of " iodine " is basically a double-edged sword, which is why opinions often differ.
It is therefore crucial for a differentiated opinion to know the individual physiological and biochemical aspects of the thyroid functions, iodine and chlorella algae.
An essential basic principle of biochemistry is also crucial, which states that the absolute majority of all metabolic processes take place on a bell-shaped curve.
There is a too little, a too much and a physiologically needs-based optimum. In other words, it's all in the dose — too much iodine isn't good, too little iodine isn't good.
The fact that every cell in the human body is dependent on the regulation of the metabolism via the thyroid hormones illustrates the importance of the micro-mineral.
Adequate nutritional iodine supply is essential not only for our basic survival, but also for overall health and maximum performance. A chronic nutritional undersupply of the trace element, on the other hand, leads in the medium and long term to an underactive thyroid gland and thus to typical symptoms such as sensitivity to cold, hair loss, listlessness, weight gain or neurological disorders.
Even in today's high-tech age, iodine deficiency is still considered the global cause of a large number of physical and cognitive disorders.
In addition to low iodine intake, too high iodine intake is also associated with an increased risk of developing thyroid-specific problems.
Because compromised thyroid functionality as a result of excessive iodine excess can manifest itself in both overfunctioning (hyperthyroidism) and underfunctioning (hypothyroidism).
In addition, from a scientific point of view, there is no doubt that excessive iodine intake can contribute to the induction or exacerbation of autoimmune thyroiditis.
Particularly in the case of genetically predisposed individuals and/or populations in iodine-deficiency areas, a selectively increased iodine supply must be viewed as a potential mechanism for the increased development of autoimmune reactivities, including lasting damage to the thyroid gland.
Especially in the case of thyroid inflammation, the essential iodine acts as an additional stressor for the organ, which can accelerate or aggravate pathophysiological conditions.
However, these and other complications can be almost completely avoided with adequate monitoring and optimal management of iodine intake.
When buying seaweed products (not to be confused with freshwater algae such as chlorella), you should therefore only use products with clearly declared information on the iodine content.
Last but not least, an insider tip: the iodine content can be manipulated by soaking and boiling the algae and can be reduced by up to 14 to 75 percent.
Is chlorella bad for the thyroid?
Against the background of the facts presented in this article, the basic application of chlorella in thyroid problems does not pose any danger.
Rather, the chlorophyll-rich freshwater algae can support a reversible restoration of optimal thyroid functionality, for example via increased heavy metal elimination or optimization of the microbiome in the intestine.
Chlorella helps the body to regain a state of immunological balance and has other multifactorial positive effects on body physiology and health.
The application of chlorella in the case of known and/or more serious thyroid problems should initially be based on a more defensive approach with a correspondingly lower starting dosage, which can then be gradually increased.
Last but not least, an optimally working thyroid gland is crucial for the realization of individual goals in terms of muscle building or fat reduction.
Hahn, A., Ströhle, A. & Wolters, M. (2005). Nourishment. physiological basics,
prevention, therapy. Stuttgart: Scientific publishing company.
Koehrle, J. (2017). Iodine metabolism and thyroid diseases. In HK Biesalski, SC Bischoff, M. Pirlich & A. Weimann (eds.), Nutritional Medicine. According to the curriculum of nutritional medicine of the German Medical Association (5th completely revised and expanded edition, pp. 980-990). Stuttgart: Thieme.