Iodine in Hashimoto: help or fire accelerant?
Some people swear by iodine drops. Others ban every last grain of iodized salt. The studies show a third picture: in Hashimoto, it comes down to the amount, the selenium supply and the inflammatory activity.
All articles from the thyroid cluster
Iodine is not a miracle remedy and not a poison. It is a building block. And with building blocks, what decides is the amount, the timing and the state of the building site.
Maybe you know this moment. You have Hashimoto, and you want to do something yourself. So you read up on it.
In the first forum, people say Hashimoto is at its core an iodine deficiency, and iodine is the missing building block. In the second forum, people say iodine is poison in Hashimoto, and even the salt in bread does harm. Both sides sound convinced. Both cite studies.
And there you are in the kitchen, salt shaker in hand, no longer sure what you are allowed to do.
I think of a patient who had started taking iodine on her own. She hoped to do her thyroid some good. At the next check-up, her antibodies were clearly higher than before. Whether the iodine was the trigger, I cannot prove in a single case. Antibodies also fluctuate on their own. But the timing made me stop and think, and it fits what controlled studies have described for decades.
In this article, I take on both extremes. Not with a new rule, but with an image you can keep in mind: a workshop where welding goes on.
What you will learn in this article
- Why both camps have a legitimate core
- What iodine does in the thyroid and where sparks arise
- What additional iodine can set off in Hashimoto
- Why iodine deficiency does harm as well
- How selenium works as a spark guard
- Why inflammatory activity is decisive
- What is well supported and what remains open
- Three levers for your everyday life
Two camps, one thyroid
In short: Both extremes have a legitimate core. It becomes a problem where a partial finding is turned into a rule for everyone.
If you feel unsure, that is not your fault. Both camps work with real observations. They simply cut different pieces out of the same curve.
Camp 1: Iodine can do everything
How it often sounds online- Hashimoto is said to be, at its core, an iodine deficiency.
- Iodine in the milligram range is said to be harmless, sometimes with reference to the diet in Japan.
- More iodine supposedly means more hormone and more energy.
- Legitimate core: Without iodine there is no thyroid hormone, and deficiency can promote goiter and nodules.
Camp 2: Iodine is poison
How it often sounds online- Iodine is said to be the trigger of Hashimoto.
- Iodized salt, dairy products and every source of iodine supposedly have to go.
- Even in pregnancy, avoidance is said to be the safe side.
- Legitimate core: Additional iodine can disturb thyroid function in Hashimoto and make antibodies visible.
So both camps are right, just not at the same time and not for everyone. Which side applies more to you depends on three things. How much iodine reaches you. How good your selenium protection is. And how active the inflammation in your gland is right now.
Many people with Hashimoto come to me with two lists. One holds supplements they are supposed to take. The other holds foods they supposedly have to avoid. When it comes to iodine, these lists almost always contradict each other.
Clinically, I observe that simply sorting through these lists together can take a lot of pressure off.
This is experience from practice, not evidence from studies.
The question is not: iodine, yes or no. The question is: how much, in what state and with which partner at its side? That partner is called selenium.
And now you know why both camps can convince you and unsettle you at the same time.
What iodine does in the thyroid, and where sparks arise
In short: Iodine is the raw material of the hormone. Reactive oxygen species arise when it is incorporated, and that is exactly where protection can be lacking.
Imagine your thyroid as a small workshop. Welding goes on there, around the clock.
The material is iodine. The thyroid actively pulls it out of the blood through a kind of pump in the cell wall. An enzyme, thyroid peroxidase, TPO for short, builds it into a large protein called thyroglobulin. The hormones T4 and T3 are made from this. T4 carries four iodine atoms, T3 three.
For welding, TPO needs a flame: hydrogen peroxide. The same molecule is found in hair bleach. It is useful, but it throws off sparks, so-called reactive oxygen species.
Against these sparks, the workshop has a spark guard. It consists of enzymes that contain selenium, above all the glutathione peroxidases. They intercept excess hydrogen peroxide before it can damage cells.
In Hashimoto, something else comes into play. There is straw lying in the workshop: immune cells that have moved in and can catch fire quickly. According to the studies I am about to show you, it seems to be mainly additional iodine above requirements that is critical. Especially when the straw is already smouldering. That is exactly what the word fire accelerant means here.
From material to fire accelerant: a possible chain
- The thyroid actively pulls iodide out of the blood through a pump in the cell wall.
- TPO builds iodine into thyroglobulin with the help of hydrogen peroxide. This produces reactive oxygen species: the sparks.
- Selenium-containing enzymes, above all the glutathione peroxidases, intercept excess hydrogen peroxide.
- In cell experiments, very large amounts of iodide led to oxidative stress and cell death in human thyroid cells.
- Heavily iodinated thyroglobulin can change its shape. In the process, new targets for the immune system can arise.
- Reviews describe that in susceptible organisms, too much iodine can increase pro-inflammatory immune cells and hold back regulatory T cells.
This chain is pieced together from cell experiments, animal models and reviews. In humans it is biologically plausible, but it has not been proven step by step.
A research team from Naples exposed human thyroid cells in the laboratory to increasing amounts of iodide. The cells died in a dose-dependent way, while reactive oxygen species and oxidised lipids increased. When the peroxidase was inhibited, the damage did not occur, and cells from other tissues did not react at all.
For you, that means: the damage appears to arise exactly where iodine is processed. This is a cell culture and not a human being, but it is an important clue to the mechanism.
Vitale M et al. Endocrinology. 2000. DOI: 10.1210/endo.141.2.7291Researchers at Johns Hopkins University examined human thyroglobulin with a series of special antibodies. When the protein was more heavily iodinated, it changed its shape: some natural recognition sites disappeared, and new ones appeared. The authors consider these new sites potentially significant in the development of autoimmune reactions.
For you, that means: a lot of iodine might change the workpiece itself so that the immune system is more likely to see it as foreign. This too is laboratory research, not proof in humans.
Saboori AM et al. Clin Exp Immunol. 1998. DOI: 10.1046/j.1365-2249.1998.00643.xSeen through the KPNI lens, iodine touches all four systems. In the hormonal system, it is the raw material for T4 and T3. In the cell's metabolism, the ratio of hydrogen peroxide to selenium enzymes determines how much oxidative stress arises. In the immune system, heavily iodinated thyroglobulin can offer new targets. And the nervous system often feels the consequences first: hypothyroidism can show up as tiredness, feeling cold and sluggish thinking.
Iodine is not the fire. Iodine is material. Whether a fire comes of it depends on how much arrives at once, how good the spark guard is and whether something in the workshop is already smouldering.
And now you know why the same substance can be both a building block and a fire accelerant.
What happens when people with Hashimoto get additional iodine?
In short: In controlled studies, even moderate additional amounts were enough to shift thyroid function in some people with Hashimoto. After stopping, this often receded.
Maybe you have bought a supplement at some point because it sounded sensible. A thyroid complex, a few drops, a seaweed capsule. The question behind it is a fair one: what does that do in Hashimoto?
A team from the University of Essen gave 40 people with Hashimoto 250 micrograms of potassium iodide daily. Their thyroid function was normal at the start. The supplementation mostly lasted four months, overall between 2 and 13 months. Another 43 comparable people received no iodine.
In the iodine group, nine cases of thyroid dysfunction occurred: eight cases of hypothyroidism, mostly mild, and one of hyperthyroidism. In the comparison group, there was a single case of mild hypothyroidism.
For you, that means: even an amount that sounds harmless can shift thyroid function in Hashimoto. All nine affected people had a hypoechoic ultrasound image, and in some of them the dysfunction receded after stopping.
Reinhardt W et al. Eur J Endocrinol. 1998. DOI: 10.1530/eje.0.1390023Important for putting this in context: in the remaining participants, function, antibodies and thyroid volume did not change meaningfully. So most people tolerated the additional amount. But not all of them. And everyone who reacted had a hypoechoic ultrasound image.
A team from the University Hospital in Mainz treated 62 people with goiter due to iodine deficiency for six months in a double-blind design. One half received 500 micrograms of iodide daily, the other half levothyroxine. In the iodine group, 6 of 31 developed high thyroid antibodies. Four of them developed hypothyroidism, two hyperthyroidism. Tissue samples from all six showed marked infiltration by immune cells.
For you, that means: in some people, iodine can set off an autoimmune reaction or make it visible. After stopping, the thyroid dysfunction receded on its own. In four of the six, the antibodies were back in the normal range three years later.
Kahaly GJ et al. Eur J Endocrinol. 1998. DOI: 10.1530/eje.0.1390290In 1971, a working group around L. E. Braverman studied seven people with confirmed or probable Hashimoto and normal thyroid function. They received five drops of a saturated potassium iodide solution daily, about 180 milligrams of iodide. Four of the seven developed hypothyroidism within four to six weeks. After stopping, the values returned to the normal range.
For you, that means: 180 milligrams is more than a thousand times the 150 micrograms that the German Nutrition Society (DGE) recommends as the daily intake for adults. Drops can contain amounts you cannot tell by looking at them. The study is small and old, but its pattern fits later controlled studies with much smaller amounts.
Braverman LE et al. J Clin Endocrinol Metab. 1971. DOI: 10.1210/jcem-32-4-515The Public Health Committee of the American Thyroid Association, ATA, has taken a position. It advises children and adults against iodine and kelp supplements containing more than 500 micrograms of iodine per day. According to the statement, some supplements contain up to a hundred times the tolerable daily upper limit.
For you, that means: people with Hashimoto are explicitly named there as a sensitive group. The society does not warn against iodine as such, but against overdosing straight from the package.
Leung AM et al. Thyroid. 2015. DOI: 10.1089/thy.2014.0331For iodine in the milligram range in Hashimoto, I have not found any controlled study that shows a benefit. Why the thyroid reacts to sudden floods of iodine with a kind of protective brake, I explain in detail in the article Putting iodine in perspective. There you will also find the hidden sources, such as seaweed, contrast media and certain medications.
Paracelsus put it in a nutshell around five hundred years ago: the dose makes the poison. In Hashimoto, a second sentence belongs with it. The state of the gland decides which dose is already too much.
If, after starting an iodine, kelp or seaweed supplement, you notice a racing heart, inner restlessness, tremor, unintended weight loss or a new, leaden tiredness, have your thyroid values checked promptly.
Never change levothyroxine or other thyroid medications on your own. And do not stop iodine-containing medications without consulting your physician.
And now you know why, in Hashimoto, a supplement that sounds harmless is a question for your physician.
So is iodine poison in Hashimoto? The other side of the curve
In short: No. Iodine deficiency does harm as well, and in a controlled study, iodine supplementation in pregnancy did not worsen the situation of TPO-positive women.
After the last section, you may want to banish every grain of iodine from your life. That would be understandable. But it would be a step into the other extreme.
Michael Zimmermann of ETH Zurich and Kristien Boelaert from Birmingham have summarised what iodine deficiency can do in populations. Early in life, it can impair cognitive development and growth. In adults, mild to moderate deficiency can promote nodular goiter and hyperthyroidism.
For you, that means: iodine is not a risk you should push down to zero. According to the authors, when intake rises in a deficiency region, mild hypothyroidism and autoimmunity increase somewhat, and whether this lasts is still open. So what you are looking for is a corridor, not a zero point.
Zimmermann MB, Boelaert K. Lancet Diabetes Endocrinol. 2015. DOI: 10.1016/S2213-8587(14)70225-6Inge B. Pedersen and colleagues from Aalborg compared two large Danish population samples before and after the introduction of mandatory salt iodization. The median urinary iodine concentration rose from 61 to 101 micrograms per litre. Afterwards, TPO antibodies were found in 23.8 instead of 14.3 percent, especially in young women and mostly at low levels.
For you, that means: even a cautious increase can make more antibodies visible in a population. Whether this is clinically significant for individual people, the study leaves open.
Pedersen IB et al. Clin Endocrinol (Oxf). 2011. DOI: 10.1111/j.1365-2265.2011.04008.xRehman Khattak, Henry Völzke and colleagues from Greifswald analysed the Study of Health in Pomerania. They compared two population samples from Western Pomerania in northeastern Germany, from around 2000 and around 2010. Iodine excretion was above 100 micrograms per litre both times, most recently at 112. The share of TPO-positive adults fell slightly during this period, from 3.9 to 2.9 percent, and goiters became less common.
For you, that means: a stable, adequate supply does not have to fuel autoimmunity. Because different tests were used, the absolute numbers can hardly be compared directly with the Danish ones.
Khattak RM et al. Popul Health Metr. 2016. DOI: 10.1186/s12963-016-0111-3One thought takes the edge off the extreme for many people: thyroid hormone itself is built from iodine. By calculation, just under two thirds of the weight of levothyroxine, also called L-thyroxine, is iodine. When the hormone is broken down in the body, this iodine is released again. So if you take levothyroxine, you never live iodine-free.
To put the amounts in context: in its 2025 derivation, the German Nutrition Society names a recommended intake of 150 micrograms of iodine per day for adults. For pregnant women it is 220, for breastfeeding women 230 micrograms. It recommends that pregnant women take an iodine supplement in addition to iodized salt, and advises consulting a physician beforehand if a thyroid condition is present.
Susanne Nøhr and colleagues from Aalborg followed 66 pregnant women with TPO antibodies in a region with mild to moderate iodine deficiency. In a double-blind design, they received a vitamin and mineral tablet with or without 150 micrograms of iodine. One group took iodine during pregnancy and breastfeeding, one only during pregnancy, and one not at all. With iodine, postpartum thyroid dysfunction did not occur significantly more often and was not more severe. The risk depended mainly on the antibody level.
For you, that means: iodine supplementation within the range of requirements does not have to be a fire accelerant in pregnancy when antibodies are present. The groups were small, and with iodine the rates were numerically somewhat higher, without a confirmed difference. The decision belongs in medical hands.
Nøhr SB et al. J Clin Endocrinol Metab. 2000. DOI: 10.1210/jcem.85.9.6799And what about leaving iodine out? There is a study from Korea that is often cited as evidence for strict avoidance. It is worth a close look.
Soo-Jee Yoon and colleagues from Seoul randomly divided 45 people with hypothyroidism due to Hashimoto into two groups. One group reduced its iodine intake to below 100 micrograms daily for three months. Afterwards, 78.3 percent in that group had normal function again, compared with 45.5 percent in the group without restriction.
For you, that means: where a great deal of iodine arrives, leaving it out can make a difference. Those who recovered under the restriction had excreted an average of 3.5 milligrams of iodine per litre of urine at the start. That is around thirty times as much as was most recently measured in Western Pomerania. This cannot simply be transferred to a supply situation like the one in Germany.
Yoon SJ et al. Yonsei Med J. 2003. DOI: 10.3349/ymj.2003.44.2.227Important: this restriction took place in a medically supervised study in people with a very high starting intake. It is no reason to stop levothyroxine or to cut out iodine on your own.
Avoidance is not automatically the safe side. It makes sense where too much arrives. Where little arrives anyway, it creates a new problem.
If you want to become pregnant, are pregnant or are breastfeeding, please do not leave out iodine out of fear. Requirements rise during this time, and your child's development depends on an adequate supply.
Clarify with your gynecologist or endocrinologist which supplementation is right for you.
And now you know why “iodine is poison” falls just as short as “iodine can do everything”.
The selenium-iodine balance: the workshop's spark guard
In short: Selenium-containing enzymes help protect the thyroid from the sparks of hormone production. Where selenium is scarce, iodine might more readily become a fire accelerant. But more selenium is not automatically better.
Maybe you have read that you should always take iodine together with selenium. As if selenium were an antidote that allows any amount of iodine. It is not quite that simple. But the idea has a legitimate core.
Lutz Schomburg of the Charité in Berlin describes the thyroid as an organ in which most of the known selenoproteins are produced. These include the deiodinases, which activate hormone, as well as glutathione peroxidases and thioredoxin reductases, which protect against oxidative damage. The gland supplies itself with selenium preferentially, largely independent of intake.
For you, that means: the spark guard is built in and is defended. In Schomburg's assessment, selenium status before supplementation might be the most important factor in whether supplementation changes anything.
Schomburg L. Nat Rev Endocrinol. 2011. DOI: 10.1038/nrendo.2011.174Sparks on one side, spark guard on the other
Iodine and hydrogen peroxide
- Raw material for T4 and T3
- Hydrogen peroxide as the flame of TPO
- An excess can increase oxidative stress
- Heavily iodinated thyroglobulin can offer new targets
Selenium and its enzymes
- Glutathione peroxidases intercept hydrogen peroxide
- Thioredoxin reductases maintain the redox balance
- Deiodinases activate and dispose of hormone
- Less iodine-related inflammation with selenium in the animal model
Schematic illustration based on the reviews by Schomburg, by Duntas, and by Hu and Rayman. Not a statement about amounts.
Qian Wu, Margaret Rayman, Lutz Schomburg and colleagues compared two counties in the Chinese province of Shaanxi whose soils contained very different amounts of selenium. They examined 6,152 people with ultrasound and blood tests. In the selenium-poor county, 30.5 percent had an abnormal thyroid finding, in the well-supplied one 18.0 percent.
For you, that means: a higher selenium level was associated with an odds ratio of 0.47 for autoimmune thyroiditis, meaning roughly halved odds. As a cross-sectional study, it shows an association, not proof of cause and effect.
Wu Q et al. J Clin Endocrinol Metab. 2015. DOI: 10.1210/jc.2015-2222Weiwei Wang, Weiping Teng and colleagues from Shenyang induced autoimmune thyroiditis with iodine in the drinking water in a mouse strain susceptible to it. Afterwards, some of the animals received selenium. In this group, thyroglobulin antibodies fell, and the inflammation in the tissue decreased over time. Protective enzymes such as glutathione peroxidase were more abundant.
For you, that means: in the animal model, selenium seems to dampen the iodine-driven fire. In humans, this has not been proven in this way.
Wang W et al. Thyroid. 2015. DOI: 10.1089/thy.2014.0568A second mouse study from Shenzhen shows the flip side. There, large amounts of iodine lowered the activity of selenium-containing protective enzymes. When the researchers additionally gave selenium, this activity was higher. So iodine and selenium are not separate topics. They interlock like material and spark guard.
A review from Athens brings both together. According to it, selenium can strengthen regulatory T cells, the peacemakers of the immune system. But the author explicitly does not want to recommend selenium across the board for everyone. Those most likely to benefit might be people with low selenium status and autoimmunity. His conclusion: a balanced selenium status and an adequate iodine supply belong together.
Shiqian Hu and Margaret Rayman come to a similar conclusion in their review. They consider adequate selenium intake crucial, especially in regions with iodine deficiency or iodine excess.
And what do studies show in which people with Hashimoto actually received selenium?
Valentina Huwiler and her team from Bern and Basel analysed 35 randomised studies on selenium in Hashimoto. In these studies, TPO antibodies fell markedly with selenium, and TSH fell slightly in people without hormone therapy. fT4, fT3, thyroglobulin antibodies and thyroid volume did not change, and side effects were as frequent as in the comparison groups.
For you, that means: selenium can move a marker. Whether how you feel moves along with it is a separate question.
Huwiler VV et al. Thyroid. 2024. DOI: 10.1089/thy.2023.0556In the Danish CATALYST trial, 412 people with Hashimoto on levothyroxine received 200 micrograms of selenium or a placebo for one year. Quality of life improved equally in both groups. At the end, TPO antibodies were lower with selenium, but the levothyroxine dose did not change as a result.
For you, that means: if your treatment is well adjusted, selenium is not a lever for big expectations. That is not an argument against measuring, but it is an argument against big promises.
Larsen CB et al. Eur Thyroid J. 2024. DOI: 10.1530/ETJ-23-0175More selenium is not more protection
Saverio Stranges and colleagues analysed a large US trial. In it, 1,202 people received 200 micrograms of selenium or placebo for an average of 7.7 years. With selenium, 58 people developed type 2 diabetes, with placebo 39, and the hazard ratio was 1.55. The risk was highest in those who already had a lot of selenium in their blood at the start.
For you, that means: selenium is a trace element with a narrow corridor. Too much can burden metabolism, which is why taking it for a longer period belongs under medical supervision.
Stranges S et al. Ann Intern Med. 2007. DOI: 10.7326/0003-4819-147-4-200708210-00175In 2023, the European Food Safety Authority, EFSA, set a tolerable upper intake level of 255 micrograms of selenium per day for adults. It also applies during pregnancy and breastfeeding. EFSA used hair loss as an early warning sign of too much. According to EFSA, the limit is exceeded mainly through high-dose supplements or the regular consumption of Brazil nuts.
Clinically, I often see selenium treated as the self-evident companion of iodine, without a value ever having been measured. My impression is that measuring first makes many decisions easier.
This is experience from practice, not evidence from studies.
Selenium is not a free pass for iodine. It is the workshop's spark guard. A good spark guard does not make a truckload of material safe. And a double spark guard does not protect twice as well.
You can find more on the selenium studies and on other building blocks in Lowering Hashimoto antibodies and in Selenium, zinc, iron and vitamin D.
And now you know why iodine and selenium should be thought of together, and both in moderation.
Why inflammatory activity is decisive
In short: The same amount of iodine can go unnoticed in a quiet gland and tip function over when the inflammation is active. Antibody level, ultrasound image and remaining function give clues.
Two people with Hashimoto take the same supplement. For her, nothing happens. For him, TSH rises. That feels unfair, but it makes biological sense.
The studies from the previous sections provide four clues as to when the balance can tip.
Four clues from the studies
- The ultrasound image. In the Essen study, all nine people who developed thyroid dysfunction on iodine had a hypoechoic image. Hypoechoic means darker, which can point to immune cells that have moved into the tissue.
- The immune cells in the tissue. In the Mainz study, all six people who developed antibodies on iodine showed marked infiltration by immune cells in their tissue samples.
- The antibody level. In the Danish pregnancy study, 35 percent of women with low TPO antibodies developed postpartum thyroid dysfunction, compared with 54 percent at medium levels and 75 percent at very high levels.
- The remaining function. In the Korean study, it was mainly people with a lower starting TSH, whose hypothyroidism was therefore less pronounced, who recovered under iodine restriction.
Active phase
Antibodies high or rising, a hypoechoic ultrasound image, the gland still makes hormone on its own. Here, studies point to a particular sensitivity to additional iodine.
Supplements only with medical supervisionMonitor over timeQuiet phase on levothyroxine
The gland hardly makes any hormone of its own anymore, and levothyroxine covers the requirement. Iodine from food then plays a smaller role in hormone production. This is physiologically plausible, but has hardly been studied specifically.
PlausibleFew studiesTrying to conceive, pregnancy, breastfeeding
Requirements rise, and the child depends on a good supply. In a Danish study, supplementation within the range of requirements did not worsen the situation of TPO-positive women.
Do not skip it out of fearAgree it with your physicianHigh iodine load in everyday life
Seaweed, kelp, drops, some medications and contrast media. This is often where the biggest practical lever lies, because the amounts can reach many times the requirement.
Take inventoryKnow your sourcesThe review from Athens describes in more detail what can happen in the immune system along the way. In susceptible organisms, too much iodine can increase pro-inflammatory Th17 cells in the gland and hold back regulatory T cells. In addition, it can drive thyroid cells into cell death via a signal called TRAIL.
A team around Noel Rose from Philadelphia describes Hashimoto as an interplay of genetic predisposition and environmental triggers. According to this review, too much iodine is one of the triggers, and in the mouse model it intensified the disease in a dose-dependent way. Why the immune system targets the thyroid in the first place, I explain in Hashimoto: causes in the immune system.
From the perspective of functional medicine, this is the heart of the matter: not a single nutrient, but the interplay. Alongside iodine and selenium, Shiqian Hu and Margaret Rayman explicitly name iron and vitamin D as factors in Hashimoto. Then there are lifestyle, stress and the gut, with more on that in Thyroid and gut. Which of these play a role for you is shown by a careful medical history, not by a forum.
The decisive question is not: what is iodine? It is: which thyroid is it meeting right now?
And now you know why the same recommendation fits one person and not another.
What is well supported and what remains open
I want to show you where the data offer solid ground and where the argument rests on plausibility or experience.
Well supported
Additional iodine can shift thyroid function and make antibodies visible in people with Hashimoto or a corresponding predisposition, often reversibly after stopping. Iodine deficiency does harm as well, especially early in life. In studies, TPO antibodies fell with selenium, without fT4, fT3 or, in CATALYST, quality of life improving.
Plausible, human data thin
Selenium as a spark guard against iodine-related oxidative stress rests mainly on cell experiments, animal models and cross-sectional data. Several small studies suggest that inflammatory activity determines sensitivity. A large study that tests this specifically is missing.
Clinical experience
Clinically, I observe that the uncertainty around iodine weighs heavily on many people, and that a sober inventory of all iodine sources can take a lot of pressure off. This is experience, not evidence from studies.
What lies between “iodine can do everything” and “iodine is poison” is not a lazy compromise. It is biology.
In the end, this is not about an element from the periodic table. It is about no longer being ground down between two camps. About being able to shop, cook and decide without fear of the salt shaker. Clarity is no small thing. Clarity is freedom.
Three levers for your everyday life
You do not have to settle the controversy for the whole world. You can sort it out for yourself. You can start these three steps right away.
Your next steps
- Take an iodine inventory. Put all your supplements on the table: multivitamins, thyroid complexes, seaweed, kelp, drops. Note the amount of iodine per day according to the label, and bring the list to your next appointment. Why the content of seaweed products varies so widely is explained in Putting iodine in perspective.
- No self-experiments with high doses. If you want to add iodine through a supplement or leave it out, talk to your practice first and have TSH and fT4 checked over time. In the studies, shifts appeared within weeks to months, and after stopping they often receded.
- Selenium by status, not by gut feeling. Have your selenium level measured before you supplement long term. More is not better: EFSA sets the upper limit for adults at 255 micrograms per day, and too much can burden metabolism.
You do not need to know whether iodine is good or evil. You need to know how much reaches you, how good your spark guard is and how your gland is doing right now. Those are three questions that have answers.
And now you know why iodine in Hashimoto is neither help in itself nor a fire accelerant in itself. It can become either, depending on the amount, on selenium and on the state of your gland.
Frequently asked questions about iodine in Hashimoto
Can I use iodized salt if I have Hashimoto?
Blanket avoidance cannot be derived from the studies. The clearest warning signals come from studies with iodine tablets, drops or very high amounts, not from the salt shaker. After salt iodization in Denmark, more people in the population had antibodies, mostly at low levels, while in Western Pomerania in Germany this was not seen over ten years. What counts is your total amount from salt, food and supplements. If the inflammation is active, the question belongs in a conversation with your physician.
Can iodine trigger Hashimoto?
Iodine is considered one of several environmental factors that, in people with a corresponding predisposition, can set off an autoimmune reaction of the thyroid or make it visible. In a double-blind study from Mainz, 6 of 31 people with goiter developed high antibody levels on 500 micrograms of iodide daily. Their tissue samples showed many immune cells. After stopping, the thyroid dysfunction receded. According to current understanding, iodine is not the sole cause here. It meets genes, the immune system and the selenium supply.
How much iodine is too much in Hashimoto?
There is no single limit that applies to everyone. In a study from Essen, thyroid dysfunction occurred in 9 of 40 people with Hashimoto on an additional 250 micrograms of potassium iodide daily, and in 1 of 43 without iodine. The American Thyroid Association, ATA, generally advises against iodine and kelp supplements with more than 500 micrograms per day and names people with Hashimoto as a sensitive group. What fits you depends on your situation and belongs in medical hands.
Is iodine poison in Hashimoto?
No. Iodine is the building block from which the thyroid makes its hormones, and T4 carries four iodine atoms. Iodine deficiency can impair cognitive development and growth early in life and can promote nodular goiter in adults. In a Danish study, 150 micrograms of iodine during pregnancy and breastfeeding did not worsen postpartum thyroid dysfunction in TPO-positive women. It is about the amount and the state of your thyroid, not about a ban.
What does selenium have to do with iodine?
When iodine is incorporated into the hormone, hydrogen peroxide is generated, a reactive molecule. Selenium-containing enzymes such as the glutathione peroxidases intercept the excess and protect the cells. If selenium is lacking, more iodine might mean more oxidative stress, as cell and animal studies suggest. In a Chinese study of 6,152 people, a higher selenium level was associated with an odds ratio of 0.47 for autoimmune thyroiditis.
Should I take selenium if I have Hashimoto?
That depends on your selenium status. A meta-analysis of 35 studies found lower TPO antibodies with selenium and, in people without hormone therapy, a slightly lower TSH, but no change in fT4 and fT3. In the CATALYST trial with 412 people on levothyroxine, quality of life improved equally with selenium and with placebo. Too much selenium can do harm, and EFSA sets the tolerable upper intake level for adults at 255 micrograms per day. A measurement before taking it for a longer period can make sense.
What does inflammatory activity mean in Hashimoto?
It means how actively the immune system is working in your thyroid right now. Clues come from the antibody level, a dark, hypoechoic ultrasound image and how much hormone the gland still makes on its own. In the Essen study, all nine people who developed thyroid dysfunction on iodine had a hypoechoic ultrasound image. In a Danish pregnancy study, the risk of postpartum thyroid dysfunction depended more on the antibody level than on iodine.
How can I have my iodine status measured?
Urinary iodine concentration is a good marker for populations, but not very reliable for individual people. In a Swiss study, excretion in the same woman varied by around a third, and about ten urine samples were needed for 20 percent precision. For populations, the WHO considers a median value of 100 to 199 micrograms per litre adequate. In practice, a careful list of your iodine sources can be useful, together with TSH, fT4 and ultrasound.
Do seaweed, kelp and iodine drops make sense in Hashimoto?
In Hashimoto, particular caution is called for here. The ATA warns that some iodine, potassium iodide and kelp supplements contain up to a hundred times the tolerable daily upper limit. In an older study, 4 of 7 people with Hashimoto developed hypothyroidism within four to six weeks on about 180 milligrams of iodide daily. After stopping, the values returned to the normal range. For high-dose iodine in Hashimoto, I have not found any controlled study that shows a benefit.
Do I need iodine in pregnancy even though I have Hashimoto?
Iodine requirements rise in pregnancy: the German Nutrition Society, DGE, names 220 micrograms per day, and 230 while breastfeeding. It recommends that pregnant women take an iodine supplement in addition to iodized salt, and advises consulting a physician beforehand if a thyroid condition is present. In a Danish study of TPO-positive pregnant women, 150 micrograms of iodine did not lead to more frequent or more severe postpartum thyroid dysfunction. Please decide this together with your gynecologist or endocrinologist.
Does levothyroxine contain iodine?
Yes. The thyroid hormone T4 carries four iodine atoms, and by calculation just under two thirds of the weight of levothyroxine is iodine. When the hormone is broken down in the body, this iodine is released again. A life entirely free of iodine is therefore not possible with levothyroxine, for biochemical reasons alone. Please never change your dose on your own.
Does a low-iodine diet make sense in Hashimoto?
For most people with Hashimoto in Germany, this is not supported by evidence. The Korean study in which more people recovered under iodine restriction involved participants with a very high starting intake, whose iodine excretion was in the milligram range per litre. In Western Pomerania, by contrast, the median value was most recently 112 micrograms per litre, and deficiency can promote problems of its own, such as goiter and nodules. Rather than blanket avoidance, it makes more sense to recognise large hidden sources of iodine.
What is the Wolff-Chaikoff effect?
It describes a protective reaction of the thyroid: when a very large amount of iodine suddenly arrives, the gland temporarily throttles the incorporation of iodine into the hormone. Normally it resumes its work after a few days. In Hashimoto, the gland seems to react more sensitively to large amounts of iodine. The ATA counts people with Hashimoto among the sensitive groups. You will find a detailed explanation in the article on iodine and the thyroid.
Further reading in context
Iodine and the thyroid
Too little, too much, seaweed, contrast media and the German numbers.
ThyroidLowering Hashimoto antibodies
What selenium, vitamin D and nutrition measurably change.
Heavy metalsHeavy metals and Hashimoto
How environmental burdens can affect the thyroid.
FastingFasting in Hashimoto
Relief for the thyroid or extra stress for the axis?
PlantsAshwagandha and the thyroid
When caution is called for with ashwagandha.
Immune systemUnderstanding autoimmune diseases
Genes, triggers and the immune system at a glance.
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