What happens if you have too much iodine in the body? The short answer is that the impact depends on your body’s unique chemistry and processing abilities, including your baseline iodine status, thyroid health, and how your body handles an iodine spike.
Consuming excessive amounts of iodized salt or trendy snacks like seaweed can quickly take your iodine levels from healthy to concerning, according to the Office of Dietary Supplements.
What happens if you have too much iodine in the body
Seaweed is notoriously rich in iodine. A single sheet of kelp often contains more iodine than the recommended daily allowance (RDA) of 150 mcg for adults. Many people who regularly consume seaweed in larger quantities, as well as those who use iodized salt or regularly eat fast food from restaurants that use iodates in dough conditioners for bread buns, unknowingly consume too much iodine.
Too much iodine in the body has several documented effects. In the thyroid, there can be the Wolff-Chaikoff effect (a temporary slowdown in thyroid hormone production through the body, one way of doing this being via the body increasing anti-TPO activity in the thyroid) or the Jod-Basedow effect (when the thyroid gland overproduces thyroid hormone). Most people trend toward hypothyroidism after iodine build-up, but some swing the other way into hyperthyroidism.
A 2025 research article shows that the body increases inflammation in multiple systems in response to iodine excess and not just inflammation regarding the thyroid via the Wolff-Chaikoff effect to suppress thyroid hormone production. Instead, inflammatory markers have been noted as correlated with iodine excess in systems such as the cardiovascular system.
Future studies on iodine excess may show just how many systems in the body demonstrate inflammation in response to iodine excess. Our founder, Marion Davis, in her recovery journey after iodine-induced hyperthyroidism, with a body now more sensitive to iodine, has noted increased joint pain after testing her current daily limit for iodine with fairly immediate symptoms afterwards, as her body slowly sheds the excess iodine built up in 2024.
Marion has consistently had positive antinuclear antibodies (ANAs) tests in her lifetime with a family history of autoimmune conditions, including siblings with Hashimoto’s thyroiditis and juvenile rheumatoid arthritis (JRA). While she has consistently tested negative for any specific autoimmune conditions, including testing negative for autoimmune thyroiditis in tests this year, there is a known trend in online communities of spinal CSF leak patients finally testing positive on specific autoimmune tests for newly developed autoimmune conditions. The question constantly emerges of what the connection is here. Most likely, as the body is complex, the cause would be multifactorial.
Previously, Marion thought that this tendency to develop an autoimmune condition was due to the stress of having a spinal CSF leak, which certainly could still play a role, with poor sleep and losing the ability to eat foods for many patients with a spinal CSF leak, and so on. However, we now also wonder whether iodine plays a factor based on noted trends in the patient population.
Our goal is not to fearmonger but to empower. If iodine plays a significant role and the solution is straightforward in the approach of staying within the U-curve of benefit for the individual, then clinicians guiding patients in moderating iodine intake and using blood work to test outcomes could potentially have a significant positive therapeutic benefit. We would never claim a single factor like iodine intake was a cure-all, but certainly, there could be substantial relief as low-hanging fruit are targeted first.
How much iodine is too much: Official limits and real-world nuance
The National Institutes of Health (NIH) sets the tolerable upper iodine intake level in the U.S. for adults at 1,100 mcg/day, which is a regulatory safety fence, not a guarantee of good thyroid health.
That said, multiple studies show long-term problems can occur even at levels only slightly higher than the recommended daily allowance of 150 mcg for non-pregnant and non-lactating adults. We can hypothesize that this is due to iodine accumulation. Anecdotally, we have observed that physicians who promote high-dose iodine supplements to patients often downplay the potential risks by suggesting that a well-functioning body can naturally eliminate any excess, much like a water-soluble vitamin. However, from personal experience, Marion has felt what iodine expulsion feels like with significant fluid shifts in her body overnight, accompanied by heavy sweating with an iodine smell in the sweat as well as frequent urination. This can lead to electrolyte imbalances as patients try to replenish fluids and overhydrate, as well as lead to headaches and fluid loss that exacerbate other conditions, such as POTS.
Additionally, the body does store some iodine rather than flush it all away, and this small stored amount often takes a long time to deplete, as the goal here from a survival perspective is that the body conserves enough iodine for the thyroid to continue functioning for several weeks to a few months, even if iodine intake stops completely. Furthermore, the body becomes more efficient if intake is low, conserving iodine and recycling it from thyroid hormones. This is why patients must be monitored carefully, and clinicians should be cautious about recommending a sudden return to the recommended daily allowance or slightly above, as Marion discovered, and as an iodine case study in research demonstrated, where the reintroduction of too much iodine for the individual, even at lower amounts, sent both into iodine-induced hyperthyroidism.
Few research studies consider long-term iodine over-intake, even at lower amounts, as well as iodine excess in patients, where their bodies were previously handling iodine efficiently due to lower intake. Population studies reveal a U-shaped risk curve for iodine: both deficiency and chronic excess raise your risk of developing goiter, hypothyroidism, and autoimmune thyroid disease, like Hashimoto’s disease. This means that both too little and too much iodine can be harmful to your thyroid health.
What are the symptoms of too much iodine?
A research article posted by StatPearls on iodine toxicity noted that the symptoms were often hard to identify as connected to iodine excess as the root cause. Milder symptoms can include nausea, vomiting, and diarrhea, but then progress to delirium, stupor, and shock. The article notes that a patient's history of consuming iodine supplements can be a clue to include iodine toxicity in the differential diagnosis. However, many physicians are not aware of other sources high in iodine, such as patients consuming iodized salt in large quantities due to sodium needs for POTS, of patients consuming high amounts of seaweed, or of patients consuming any other known or hidden sources of iodine or iodates regularly and in high quantities. Questions regarding diet notoriously are not common in the U.S. in physician consultations with patients.
We have observed that patients often begin to recognize the pattern and report being allergic to iodine. As Marion has experienced, the level of iodine excess in her body determines which foods she can tolerate. For instance, she would feel nauseous after eating eggs, but this nausea would disappear as her iodine excess gradually decreased from 2024. Her body became more tolerant of a slightly higher daily iodine intake (but still far below the recommended daily allowance, with medical guidance).
Similar to other patients, Marion has noted a unique trend with iodine-induced nausea, and that is the smell of seawater, as the sea has a smell likened to iodine. At times, when she has eaten more iodine than her body could handle, she started feeling nauseous with the sensation that she had swallowed a lot of seawater that she needed to vomit. At other times, she noted an ocean-like smell in her sweat, which is a unique symptom that other patients have reported as well, especially spinal CSF leak patients with hypothyroidism who had consumed iodine supplements. While physicians likely would be skeptical of such a unique symptom, search queries pop up on Google and in forums asking, “Why do I smell like the ocean?” Weirdness happening in trends is almost always helpful data.
Symptoms of iodine deficiency or excess can also be those related to thyroid dysfunction in general, as this deficiency or excess can cause thyroid disorders. These symptoms include fatigue, weight change, palpitations, anxiety, heat or cold intolerance, and a visible or palpable goiter (enlarged thyroid gland). Excess iodine consumption can also worsen or trigger autoimmune thyroiditis (for example, Hashimoto’s) in vulnerable populations, sometimes without exhibiting classic symptoms at first.
Start a conversation with your clinician if you experience any of these symptoms after starting a high-iodine diet or supplement.
Is 250 mcg of iodine too much?
The short answer is: sometimes. Some clinical trials and case reports show that individuals whose bodies are more sensitive to iodine (for example, people with autoimmune tendencies and/or from low-iodine regions where their bodies are using iodine more efficiently) can develop hypothyroidism or hyperthyroidism consuming as little as 250 mcg of iodine daily. Autoimmune tendencies refer to the body's immune system mistakenly attacking its own tissues, which can affect the thyroid gland in the case of iodine sensitivity.
Keep in mind that past iodine intake can also be an influential factor if your body has become more efficient in iodine usage.
Excess iodine causes hyperthyroidism — When does that happen?
Yes, excess iodine causes hyperthyroidism in some people, particularly those with preexisting nodular thyroid disease, those given a sudden extremely high dose of iodine, and/or in those individuals who have shifted rapidly from deficiency to repletion.
The Jod-Basedow phenomenon can appear in people with normal iodine intake who suddenly consume vast amounts of iodine or even after iodine is reintroduced at a lower amount than the upper limit to a previously deficient population or individual, such as shown in the research study on 250 mcg/day supplements where this sent one person into hyperthyroidism or in the case study on a 150 mcg/day supplement with the patient also rapidly adding in iodine-rich foods after eating very little iodine for three years. But it’s not the only possible outcome.
How clinicians and researchers judge the evidence
- Many population studies are cross-sectional (one point in time) and can show associations (U-shaped risk), but they can’t prove cause-and-effect. Sample sizes and how iodine was measured (spot urine vs. 24-hour collections vs. dietary recall) vary a lot.
- Some supplementation trials that reported adverse medical effects had small sample sizes, lacked baseline iodine measurements, and failed to control participants’ dietary iodine. These limitations make it difficult to attribute outcomes to the supplement. That’s why individualized assessment of iodine status is crucial, as it takes into account your unique body and dietary habits.
What to do if you think you’re eating too much iodine
Here’s a short checklist to work through if you think you’re consuming too much iodine:
- Audit your diet: Calculate your daily iodine intake by counting obvious sources, such as seaweed (nori/kelp), iodized salt, some seafood, seaweed snacks, and kelp supplements.
- Get tested: Urine iodine tests can estimate recent intake, but vary significantly based on how much you ate just recently and not how much your body has stored and how efficiently your body is using iodine. A complete thyroid panel (TSH, free T4, free T3) plus thyroid autoantibodies gives better insight into how iodine affects your thyroid as an individual. A single urine test won’t tell the entire story.
- Work with your team: Consult with a primary-care physician (PCP), endocrinologist, and dietitian if you have symptoms of thyroid dysfunction. Discuss with your team a gradual reduction of high-iodine foods if you are over the recommended daily allowance rather than making abrupt changes and ask for guidance in replacing any nutritious high-iodine foods with lower-iodine options, ensuring you maintain a healthy diet. For instance, if you are keeping your high cholesterol in check via Omega 3 in a diet full of fatty fish, ask your dietitian how you can continue to keep a solid Omega 3 to 6 balance if you reduce the amount of fish you eat per week.
- Learn more: Our course with registered dietitian Vincci Tsui empowers you to take control of your health. It walks you through auditing your dietary iodine, performing “iodine swaps,” and using research sources to self-advocate with your medical team for better nutrition-based thyroid care, giving you the knowledge to make informed decisions. Please note that this educational course is not a substitute for professional medical advice. Patients should consult with their healthcare team, including their primary care physician, endocrinologist, or registered dietitian, to determine the best course of action for their individual needs.
