Iodine-Induced Thyroid Dysfunction Explained: Causes, Risks & Insights

Revisiting this trace mineral arose for two reasons.

1.Inspite universalization of iodized salt in India thyroid cases are rising today at rates higher than ever in past.

2. Added Iodine in salt is very sensitive to temperature, exposure to sun, heat and other conditions and degrades from manufacturing to end user that is why its mandated that production stage must be higher at production stage than sales stage and sales stage higher than user stage and lot of loss can happen at using stage ---thus we have no idea of what is happening and that is why in USA iodine deficiency in spite universalization of iodized salt –thyroid cases are on rise.

3. A doctor friend of mine literary jolted me about hydrogen peroxidization in thyroid gland. Hydrogen peroxidization is necessary function of thyroid gland ----but that has to be within normal parameters. But now we are getting elevated reports of this being the cause of thyroid malfunctioning and researchers are wondering what can be reason and I join that bandwagon ---since what we use as iodine in salt is unstable compound and there are several sources of its production ---we know very little of what is used and not many detailed researches have been done over the time years about its downstream effects. Is just adding iodine sufficient. In fact, these questions were even raised when GOI decided to go via iodized salt and it was said a big industrial house which was not able to push salt sales lobbied a lot for pushing iodized salt and proved a wealth mine for them. It is not our job here to go in that ---we just are raising the issue from functional health issue.

Iodine is a mineral nutrient essential for the regulation of a variety of key physiological functions including metabolism and brain development and function in children and adults. Iodine, a trace element, is an essential component of thyroid hormones thyroxine (T4) and triiodothyronine (T3), which are critical for liver, kidney, muscle, brain, and central nervous system function. Iodine regulates overall metabolism and plays a critical role in fetal and child neurodevelopment, organ, and tissue function. A healthy adult body contains 15–20 mg of iodine, of which 70–80% is in the thyroid gland. For the developing fetus, deficiency is one of the greatest causes of preventable intellectual disability, thus iodine status of pregnant and women of reproductive age is a recognized international concern.

Iodine is the heaviest stable halogen element and primarily exists in nature as iodide (I-), the form typically used to produce supplements and iodized table salt in the form of potassium iodide (KI). It can also be found naturally as iodate (IO3-), another form used to fortify table salt as potassium iodate (KIO3). Iodide is naturally in soil and seawater, which affects the iodine content of produce. However, in many regions surface soils are depleted of iodide. Since iodide is found in seawater, it volatizes into the atmosphere and can return to the soil. In non-coastal regions this cycle is incomplete and as a consequence plant food and drinking water are depleted.

In the human gut iodine is metabolized to iodide and in healthy adults > 90% is absorbed. Once in circulation, it mainly accumulates in the thyroid gland or is excreted by the kidney, with small amounts accumulating in the salivary glands, mammary gland, or choroid plexus. Clearance by the kidney is constant, while uptake by the thyroid is dependent upon iodine status and intake. When iodine supply is sufficient, uptake by the thyroid may be ≤10%, whereas it can exceed 80% due to chronic deficiency.

After active transport into the thyroid, iodide is stored in the thyroglobulin (Tg) protein before undergoing conversion into T3 and T4. The hormones T3 and T4 enter circulation bound to carrier proteins and then target tissues; however, T3 is the primary physiologically active form and preferentially binds to its receptors. Both free T3 and T4 are assessed in serum by immunoassay. However, serum thyroid stimulating hormone (TSH) is the best marker of individual thyroid status and is used clinically for this purpose. The hormones T3 and T4 do not change sufficiently as a result of iodine deficiency to be clinically useful.

Over 90% of ingested iodine is excreted in the urine by the kidneys, which is why measurement of UIC is considered one of the best biomarkers of recent dietary iodine intake. The hormone TSH, secreted by the pituitary gland, is the main regulator of T3 and T4 metabolism through a negative feedback loop regulated by thyroid hormones and modulated by TSH-releasing hormone. In addition to signaling degradation of Tg and release of T3 and T4 into the circulation, TSH also increases iodine uptake; therefore, an elevated TSH concentration is generally a symptom of hypothyroidism, while low TSH levels indicate hyperthyroidism.

To maintain homeostasis and hormone synthesis, the thyroid absorbs 50–60 µg/day of iodine when supply is sufficient. The daily recommended dietary allowance (RDA) established by the Institute of Medicine (IOM) is 90 μg for children 1–8 years old, 120 μg for children 9–13 years old, 150 μg for males and most females ages 14 and older, 220 μg for pregnant women and 290 μg for lactating women. The daily Tolerable Upper Intake Level (UL) for individuals over age 18 not receiving iodine for medical reasons is 1100 μg.

Severe growth curve of thyroid in last two decades is upfront fact. Though some people claim it’s because of better detection but application of observational mind –it is on a growth trajectory.

Iodine Induced Dysfunction of Thyroid:

“This study is the first comprehensively performed a scientometric analysis exploring the research trends and hotspots of iodine-induced thyroid dysfunction from 2000 to 2022. The development of iodine-induced thyroid dysfunction has progressed through a three-stage development period from 2000 to 2022” (Boshen Gong et. el 2023)—established based on retrieved data came to conclusion of its growing roots and conclusion that iodine induced dysfunction of thyroid gland.

Iodine is essential in thyroid hormone production. Iodine deficiency is associated with serious complications (i.e. miscarriage and stillbirth), whereas excess can cause thyroid dysfunction (i.e. hyperthyroidism, hypothyroidism, thyroid autoimmunity).

The WHO and the International Council for the Control of Iodine Deficiency Disorders adopted a global framework to prevent iodine deficiency. The use of iodized salt has been found to reduce iodine deficiency disorders and alter the pattern of thyroid illness. Nonetheless, one significant effect of excessive iodine on thyroid function is termed the Wolf-Chaikof effect or long-term hypothyroidism caused by excess consumption of iodine. In addition, thyrotoxicosis associated with elevated iodine levels can cause acute toxic damage. There is a well-established relationship between population iodine intake and nonautoimmune thyroid disorders, though there is less clarity on iodine's role in AITDs (Teti C et. el 2021).

“Iodine supplementation increases the frequency and severity of autoimmune thyroiditis in animal models, which is consistent with epidemiological studies. Iodization of salt remains the most successful strategy to eradicate iodine deficiency in human diets. However, the hazards (and iodine induced hyperthyroidism, in particular) exceed the advantages. (Iyshwarya Bhaskar Kalarani and Ramakrishnan Veerabathiran 2022).

Issues with Iodized Salt and Iodine for Thyroid.

“Among the 51,637 subjects included in this study, the prevalence of thyroid nodules was 40.25%, and the prevalence of thyroid cancer was 0.76%; among all enrolled subjects, only 3.59% had a daily iodized salt intake less than 5 g. In addition, we found that a daily intake of more than 5 g of iodized salt was not only an independent risk factor for the occurrence of thyroid nodules (odds ratio (OR): 2.08, 95% confidence interval (CI): 1.86–2.31, p < 0.001) but also an independent risk factor for the occurrence of thyroid cancer (OR: 5.81, 95% CI: 1.44–23.42, p = 0.012). A pooled analysis showed a significantly higher risk of thyroid nodules in subjects aged > 60 years with a daily iodized salt intake of more than 5 g compared to subjects aged < 60 years with a daily iodized salt intake of no more than 5 g (OR: 4.88, 95% CI: 4.29–5.54, p < 0.001); the risk of thyroid cancer was not significantly different between subjects aged > 60 years with a daily iodized salt intake of more than 5 g and those aged < 60 years with a daily iodized salt intake of no more than 5 g (OR: 2.15, 95% CI: 0.52–8.95, p = 0.281). The risk of thyroid nodules was not increased in physically active subjects with a daily iodized salt intake of more than 5 g compared to physically inactive subjects with a daily iodized salt intake of no more than 5 g (OR: 1.12, 95% CI: 0.97–1.28, p = 0.111). The same protective effect of physical activity was observed for thyroid cancer in subjects whose daily iodized salt intake exceeded 5 g. The risk of thyroid nodules was reduced for subjects with an education level of postgraduate and above, even when the daily iodized salt intake exceeded 5 g, compared to those with high school education and below and a daily iodized salt intake of no more than 5 g (OR: 0.79, 95% CI: 0.66–0.93, p = 0.005); however, a protective effect of education level on the occurrence of thyroid cancer was not observed.

Independent risk factors affecting daily iodized salt intake greater than 5 g included age, triglycerides, family history of tumors, physical activity, and marital status.” ( Yaohui Wang et al 2021).

Aiman Khudair et al 2025 “In summary, while iodine is essential, excess intake can have detrimental effects on various physiological systems. IE is associated with increased inflammatory markers, OS, and vascular dysfunction, contributing to cardiovascular issues such as hypertension and atherosclerosis. Additionally, high iodine intake may elevate the risk of TC, particularly through genetic mutations and cellular mechanisms promoting cancer cell proliferation. Iodine-induced autoimmunity, including conditions like GD and HT, also underscores the negative impact of excessive iodine on immune health, with mechanisms involving immune cell polarization and gut microbiota changes. Moreover, elevated iodine levels give rise to neurotoxic effects, affecting brain development and dopamine function. In addition, excess iodine can have a nephrotoxic effect, leading to the risk of acute kidney injury and damage to the renal system.”

So possibly time to test whether we are exposing ourselves to excessive iodine by intaking iodized salt. So possibly we can do with using maximum salt as non-iodized salt and limited quantity of iodizes salt it will solve two problems, we will get iodine and since iodized salt is more acute in taste it will reduce the need of salt in quantity.

For adults, WHO recommends less than 2000 mg/day of sodium (equivalent to less than 5 g/day salt (just under a teaspoon). For children aged 2–15 years, WHO recommends adjusting the adult dose downward based on their energy requirements. And want it to be implemented globally by 2025.

With iodized salt the norm ----more salt we take not only sodium increases even iodine intake increases.