Can Excess Iodine Cause Hypothyroidism? Recommended Usage, Risk Factors & Warnings

The chemical element iodine is crucial for the human body. However, your body lacks the ability to produce its own iodine content, and therefore iodine has to be included in food. The most direct and common form of iodine content in our daily diets is salt. Iodine is necessary for the development of thyroid glands, growth and development. Even with the plethora of uses it encompasses, iodine consumption has to be controlled because overdosing of anything is [1]  simply not good for your body.

Long-term and excessive use of iodine has been proved to be unsafe [1]  for your body. It can cause various side effects in some people, with the common ones being nausea, stomach pain, runny nose, headache, metallic taste, and diarrhoea. The side effects of iodine poisoning can impact different people, differently. In some of the extreme cases, it can even result in angioedema. Apart from the natural iodine content, it is also obtained through the consumption of iodine[2]  supplements.

excess iodine image

Iodine can enter your body through food and can be applied on the skin. Studies have revealed that iodine overdosing is not rare and is commonly found in people who regularly consume salty foods or iodine-rich food [3] such as seaweed, tuna, shrimp etc. Get to know the symptoms of excess iodine - what it does to you and your body!

What Are The Symptoms Of Excess Iodine?

The chances of consuming excess iodine are sort of normal, especially if your diet is comprised [4]  of seafood, eggs, prunes etc. You may not know that you are consuming excess iodine, so here are the most common symptoms to help you understand.

excess iodine symptom

What Is The Daily Recommended Dosage Of Iodine?

The amount of iodine you need on a daily basis is highly dependent on your age (in micrograms).

  • Newborns to 6 months - 110 mcg
  • Infants (7-12 months) - 130 mcg[5]
  • Children (1-8 years) - 90 mcg
  • Children (9-13 years) - 120 mcg
  • Teens (14-18 years) -150 mcg
  • Adults - 150 mcg
  • Pregnant teens & women - 220 mcg
  • Breastfeeding teens & women - 290 mcg

How Much Is Too Much?

The excessive consumption of iodine has been proven to have a plethora of side effects. With the common side effects being headache and metallic taste etc., it can have severe side effects such as swelling of the lips and face (angioedema), fever, joint pain, severe bleeding and bruising, allergic reactions including hives, lymph node enlargement, and even in some extreme [6]  cases - death.

The maximum limit of iodine daily dose it as mentioned below (in micrograms)

  • Newborns to 12 months - Not established [7]
  • Children (1-3 years) -200 mcg
  • Children (4 - 8years) - 300 mcg
  • Children (9 - 13 years) - 600 mcg
  • Teens (14 - 18 years) - 900 mcg
  • Adults - 1,100 mcg
  • Pregnant teens (14 - 18 years) - 900 mcg
  • Pregnant teens & women (over 18 years) - 1100 mcg

What Are The Risk Factors?

Contrary to the common belief which suggests that consumption of iodine supplements are the cause of excess iodine content, certain components [8]  can make you sensitive to iodine elevating the risks of developing iodine poisoning.

The risk factors pertaining to the consumption of excess iodine are

  • Graves' disease.
  • Goitres.
  • Hashimoto's thyroiditis. 
  • The iodine supplements can combine with the anti-thyroid medications such as methimazole, and cause [9] your body to produce a limited and restricted amount of thyroid hormone. 
  • Supplements such as potassium iodide can interact with medicines for high blood pressure and hike the amount of potassium level in the blood to an unsafe level.

What Is The Diagnosis?

If you suspect that you are suffering from any of the above-mentioned symptoms, it is advisable that you immediately go to the hospital. The diagnosis will depend on the severity [10]  of your symptoms.

1. Doctor's evaluation - The doctor may give you medication to vomit. This is done so as to pump out your stomach. The doctor may give you activated charcoal, so as to help your body from absorbing the iodine.

2. Blood tests - The blood tests are done to determine the levels of thyroid [11]  hormones and thyroid-stimulating hormone (TSH).

3. Imaging tests - Imaging tests[12] will also be done to get a clearer idea and picture of your condition.

What Are The Treatments?

The treatments for excess iodine consumption or iodine poisoning depends on the severity of the condition. In milder cases, getting immediate medical help [13]  can aid in avoiding any long-term and lasting problems. However, severe cases can result in causing long-term effects. It is critical that you get medical help in the event[14]  of iodine poisoning.

1. Dietary changes - Individuals are advised to use salt that is not fortified with iodine. Also, to reduce the consumption of iodine-containing food such as seafood, seaweed, yoghurt, and milk.

2. Thyroid hormones - In the event of hypothyroidism due to too much iodine consumption, consuming less iodine can cure the disorder. But, some individuals will be advised to take thyroid hormones [15]  for a longer period of time, sometimes lifelong.

What Are The Precautions & Warnings?

1. During pregnancy and breastfeeding - It is advised not to take more than 1100 mcg of iodine per day if you are over 18 years old. If you are 14 to 18 years old, do not take more than 900 mcg of iodine per day. Avoid the high dose consumption [16]  through the mouth, as applying it to the skin is applicable during pregnancy and breastfeeding.

2. Dermatitis herpetiformis - A type of rash, dermatitis herpetiformis can worsen in the case of regular iodine[17]  consumption.

3. Autoimmune thyroid disease - Individuals diagnosed with the thyroid problem are sensitive to iodine and the harmful side effects of the element.

4. Thyroid disorders - Individuals suffering from thyroid disorders such as hypothyroidism, goitre or a thyroid tumour can be negatively impacted by regular iodine [18] consumption as it will worsen the conditions.

Can Too Much Iodine Cause Hypothyroidism?

According to various studies, consumption of an excess amount of iodine is not a direct factor in causing[19] hypothyroidism. That is, individuals who are already suffering from thyroid related issues and risk factors are easily prone to the develop hypothyroidism in the event of excessive iodine intake, which is termed as iodine-induced thyroid dysfunction. The thyroid dysfunction can be overt or sub-clinical, and the source of the excess iodine[20]  may not be recognisable.

View Article References
  1. [1] Burman, K. D. (2015). Introduction. In A Case-Based Guide to Clinical Endocrinology (pp. 121-125). Springer, New York, NY.
  2. [2] Harding, K. B., Peña‐Rosas, J. P., Webster, A. C., Yap, C. M., Payne, B. A., Ota, E., & De‐Regil, L. M. (2017). Iodine supplementation for women during the preconception, pregnancy and postpartum period. Cochrane Database of Systematic Reviews, (3).
  3. [3] Nyström, H. F., Brantsæter, A. L., Erlund, I., Gunnarsdottir, I., Hulthén, L., Laurberg, P., ... & Meltzer, H. M. (2016). Iodine status in the Nordic countries–past and present. Food & nutrition research, 60(1), 31969.
  4. [4] Zimmermann, M. B., & Galetti, V. (2015). Iodine intake as a risk factor for thyroid cancer: a comprehensive review of animal and human studies. Thyroid research, 8(1), 8.
  5. [5] La Vecchia, C., Malvezzi, M., Bosetti, C., Garavello, W., Bertuccio, P., Levi, F., & Negri, E. (2015). Thyroid cancer mortality and incidence: a global overview. International journal of cancer, 136(9), 2187-2195.
  6. [6] Thompson, J. J., & Manore, M. (2015). Nutrition for Life: Books a la Carte Edition. Benjamin-Cummings.
  7. [7] Whitney, E. N., & Rolfes, S. R. (2018). Understanding nutrition. Cengage Learning.
  8. [8] Burman, K. D. (2015). Introduction. In A Case-Based Guide to Clinical Endocrinology (pp. 121-125). Springer, New York, NY.
  9. [9] Völzke, H., Caron, P., Dahl, L., De Castro, J. J., Erlund, I., Gaberšček, S., ... & Karanfilski, B. (2016). Ensuring effective prevention of iodine deficiency disorders. Thyroid, 26(2), 189-196.
  10. [10] Zhao, W., Zhang, Z., Han, D., Yang, J., Liu, C., & Zhao, W. (2015). Iodine Concentration on Dual-energy Contrast Enhanced CT in Differential Diagnosis of Thyroid Nodules. Chinese Journal of Medical Imaging, (11), 815-818.
  11. [11] Hardley, M. T., Chon, A. H., Mestman, J., Nguyen, C. T., Geffner, M. E., & Chmait, R. H. (2018). Iodine-Induced Fetal Hypothyroidism: Diagnosis and Treatment with Intra-Amniotic Levothyroxine. Hormone research in paediatrics, 1-5.
  12. [12] Gandhi, A., Wong, K. K., Gross, M. D., & Avram, A. M. (2016). Lingual thyroid ectopia: diagnostic SPECT/CT imaging and radioactive iodine treatment. Thyroid, 26(4), 573-579.
  13. [13] Yu, C. Y., Saeed, O., Goldberg, A. S., Farooq, S., Fazelzad, R., Goldstein, D. P., ... & Goldsmith, C. H. (2018). A Systematic Review and Meta-analysis of Subsequent Malignant Neoplasm Risk after Radioactive Iodine Treatment of Thyroid Cancer. Thyroid, (ja).
  14. [14] Orgiazzi, J. (2018). Which Factors Predict the Outcome of Ablative Radioactive Iodine Treatment of Hyperthyroid Graves' Disease?. Clinical Thyroidology, 30(11), 500-504.
  15. [15] Wallner, L. P., Reyes-Gastelum, D., Hamilton, A. S., Ward, K. C., Hawley, S. T., & Haymart, M. R. (2018). Choice of radioactive iodine treatment for thyroid cancer: Results from a population-based survey.
  16. [16] Pearce, E. N., Lazarus, J. H., Moreno-Reyes, R., & Zimmermann, M. B. (2016). Consequences of iodine deficiency and excess in pregnant women: an overview of current knowns and unknowns. The American journal of clinical nutrition, 104(suppl_3), 918S-923S.
  17. [17] Kárpáti, S. (2015). Dermatitis herpetiformis. In Blistering Diseases (pp. 441-447). Springer, Berlin, Heidelberg.
  18. [18] Smith, T. J., & Hegedüs, L. (2016). Graves’ disease. New England Journal of Medicine, 375(16), 1552-1565.
  19. [19] Leung, A. M., & Braverman, L. E. (2012). Iodine-induced thyroid dysfunction. Current opinion in endocrinology, diabetes, and obesity, 19(5), 414.
  20. [20] Leung, A. M., & Braverman, L. E. (2014). Consequences of excess iodine. Nature Reviews Endocrinology, 10(3), 136.
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