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Iodine Allergy: The Truth Behind Your Allergic Reaction

Written by Dr. Group, DC Founder
A bowl of salt. Iodine is not the cause of allergic reactions in iodine-rich foods.

Iodine is an essential trace mineral that supports the body’s production of thyroid hormones, which regulate metabolism — the chemical reactions that occur in every cell in the body and provide energy for life.

So how could someone be allergic to a vital nutrient? Well, because iodine is not the actual cause of allergic reactions. Research has shown that the adverse reactions occurring in association with iodine-rich foods like seafood or shellfish, iodine antiseptics, and radiocontrast dyes are the body’s response to other chemicals or allergens found with iodine but not to iodine itself. The revelation that iodine is, in fact, not an allergen is good news for anyone who believes they have an iodine allergy yet wants to take an iodine supplement.[1]

Iodine is not the cause of allergic reactions from iodine-rich foods. These adverse responses are associated with other chemicals found in foods or products like seafood, shellfish, iodine antiseptics, and radiocontrast dyes.

What Does Iodine Do in the Body?

Iodine is an essential nutrient that regulates metabolism, sustains energy levels, and supports hormone synthesis.[2] This mineral is particularly important in the thyroid, a bow tie-shaped gland just above the larynx or Adam’s apple, where it supports the creation of the thyroid hormones thyroxine (T3) and triiodothyronine (T4). These thyroid hormones regulate metabolism and influence the body’s sensitivity to adrenaline, norepinephrine, and other hormones. Some research even suggests that iodine supports brain health and IQ levels.[2, 3] Although iodine is a vital nutrient, it’s even more critical for women who are pregnant or lactating as it supports bone and nervous system development in children.

How Much Iodine Is Necessary?

The National Institutes of Health recommends adults get 150 mcg (micrograms) per day, while pregnant women should get 220 mcg per day and lactating women 290 mcg per day.[4] The NIH also recommends an upper limit on iodine of 1,110 mcg while some practitioners recommend mega-servings. Many experts believe that the recommended daily allowance of 150 mcg is too low. Larger servings of iodine can increase the amount of toxic metals the body excretes, and Japanese citizens, who have the world’s highest iodine intake, have better breast and prostate health.[4]

What Happens if I Don’t Get Enough Iodine?

On a global scale, the World Health Organization (WHO) estimates one-third of the world’s population is at risk for iodine deficiency.

Many people struggle to get enough iodine in their diet. The "standard American diet" (SAD), which generally contains a lot of processed foods and vegetables grown in nutrient-depleted soils, doesn’t always provide a full spectrum of nutrients. On a global scale, the World Health Organization (WHO) estimates that, as of 2004, two billion people are at risk for iodine deficiency.[5]

The consequences of iodine deficiency range from mild to severe. On one end of the spectrum, too little iodine leads to brain fog, memory loss, and low energy levels. Serious deficiencies can lead to conditions like hypothyroidism or goiter.[6]

What Causes an Allergic Reaction?

An allergy occurs when your body responds to some external allergen that causes an immune response. An encounter with an element like dust, pollen, or shellfish sets off a reaction, and the immune system produces antibodies to attack the allergen (which is an antigen). This tells the body to produce histamines that make blood vessels expand and cause other common allergy symptoms.

YouTube Video

Allergic to Iodine?

Length: 2 minutes

Why Do People Associate Iodine with Allergies?

If iodine is an important nutrient, how can someone be allergic to it? The short answer is that they can’t. While there’s no question that some people have an adverse reaction to shellfish, radiocontrast dyes, and topical antiseptics that contain iodine, there is a question as to what prompts that reaction.

It turns out that the iodine molecule is too small and simple to cause an antibody response, which is why scientists ruled it out as an allergen. However, iodine could theoretically act as a hapten — a molecule that's too small to cause issues by itself but can combine with another substance to stimulate an antigen-antibody response.[7, 8, 9, 10]

Iodine & Shellfish Allergies

The high iodine content of seafood and shellfish, such as lobster and shrimp, led some people to believe that this nutrient causes allergic reactions when certain people consume it. The symptoms of shellfish allergy can range from mild to severe, with some severe allergic responses causing anaphylactic shock, a potentially fatal condition.[7]

The truth is that shellfish allergies are caused by four proteins found in the food and not the iodine.

This myth that iodine is to blame persists, despite evidence to the contrary. One 2005 study of 60 patients with a confirmed shellfish allergy found that 92 percent believed iodine was responsible for their allergic reaction rather than something else in the shellfish. Most of those respondents received their information on the internet or in a magazine.[9]

The truth is that scientists have ruled out iodine as the cause of these allergic reactions after identifying four proteins from shellfish that cause an allergic response: tropomyosin, arginine kinase, myosin light chain kinase, and sarcoplasmic calcium-binding protein.[1, 9]

Allergy to Iodine-Based Contrast Dyes

To improve the quality of images produced from x-rays and computed tomography (CT) scans, doctors may use an iodine-based radiocontrast dye. Contrast dyes help to reveal irregularities that might otherwise be missed.[10, 11] Around one to 12 percent of people react to contrast dyes, with less than one percent experiencing severe reactions. The risks are higher with the older, ionic iodine-based radiographic dyes, and reactions have been reduced even further with newer, non-ionic dyes.[12] Itchy skin accounts for 70 percent of the reactions to the radiocontrast dye.[12]

As a result of the reactions, it was believed that the iodine in this solution was responsible. However, several studies have found that antibodies do not form after exposure to iodine-dye combinations; thus any reactions that occur are not allergies, per se, but an activation of the nonspecific immune system. A true allergy can only occur the second time one encounters a substance because the immune system must have formed antibodies to protect against it. One study showed that zero of 23 patients with previous sensitivity to contrast dye reacted to sodium iodide injected under the skin.[1, 12] Hence, the reaction to radiocontrast dyes is considered an allergy-like reaction rather than a true allergy.

Those who suffer from asthma and cardiomyopathy have a greater chance of experiencing a reaction to iodine-based contrast dyes. The severity of the response is linked to age, gender (females are more likely to be affected), and the use of ACE inhibitors and beta-blockers.[1]

Topical Iodine Allergy

Povidone-iodine solution is often used as an antiseptic to treat skin abrasions or to disinfect the skin before and after surgery. Some patients treated with povidone-iodine solution developed an itchy "iodine rash." Other patients who previously had a response to povidone-iodine antiseptics had no reaction when treated with potassium-iodide, thus indicating that other chemicals are the cause of reactions, not iodine itself.[12, 13]

Healthy Sources of Iodine

Since our bodies don't produce iodine, an iodine-rich diet or supplements are essential to sustain healthy levels of this trace element.

Dietary Sources of Iodine

Iodine is present in the soil, so vegetables grown in regions that are iodine-rich will naturally have more iodine, though most people are not familiar with whether their produce is grown in iodine-rich soil. Foods naturally high in iodine include seaweed and kelp, lima beans, and fruit like plums, cranberries, and strawberries.

Iodized Table Salt and Sea Salt

Some people think that salt has a lot of iodine, but this is not necessarily true. There are two main types of salt used for cooking and consumption: table salt and non-iodized natural salts like sea salt or Himalayan crystal salt. "Iodized" table salt has been supplemented with iodine since 1924 to reduce iodine deficiency.

Non-iodized salt is the healthier option as it is natural and minimally processed. This status enables sea and rock salt to retain other minerals like magnesium, calcium, and potassium. One might think that non-iodized salt would have less iodine than iodized table salt, and some sea and rock salt does contain less, but some varieties of Himalayan crystal salt contain more iodine than table salt. Sea salt typically has a small amount of iodine, while iodized table salt has more.

Iodine Supplements

If you live in a landlocked area, your food is grown in low-iodine soil, or you’re switching away from iodized table salt as a source of iodine, you may benefit from an iodine supplement. Keep in mind that iodine supplements vary in quality and nascent iodine is the most beneficial.

Can I Have an Allergic Reaction to Iodine Supplements?

As explained above, iodine itself does not cause an allergic reaction, but some supplements may contain other chemicals that can cause an allergic response. If you have any allergies, your risk of additional allergies might be higher. In this case, look for an iodine supplement that’s free of additives.

Detoxadine® is a premium-quality, deep-earth sourced nascent iodine supplement that supports thyroid health, the immune system, and more. Made from iodine, vegetable glycerin, and water, it’s a pure formula and one of the easiest ways to ensure healthy iodine intake.

References (14)
  1. Iodine allergy and contrast administration. UCSF Department of Radiology & Biomedical Imaging. University of California. ucsf.edu. Accessed 18 Jan 2018.
  2. Raffensberger L. How Adding Iodine to Salt Boosted Americans’ IQ. Discover Mag. Jul 2013. Accessed 15 Feb. 2018.
  3. Feyrer J, et al. The Cognitive Effects of Micronutrient Deficiency: Evidence from Salt Iodization in the United States. National Bureau of Economic Research Working Paper No. 19233. Jul 2013.
  4. Aceves C, et al. The Extrathyronine Actions of Iodine as Antioxidant, Apoptotic, and Differentiation Factor in Various Tissues. Thyroid. 2013; 23(8):938-946.
  5. Andersson M, et al. Iodine deficiency in Europe: A continuing public health problem. World Health Organization. 2007. Accessed 15 Feb. 2018.
  6. Salisbury S. Cretinism: The past, present and future of diagnosis and cure. Paediatr Child Health. 2003; 8(2):105-106.
  7. Woo C, et al. Not all shellfish ‘allergy’ is allergy!. Clin Transl Allergy. 2011;1(1):3.
  8. Schabelman E,et al. The relationship of radiocontrast, iodine, and seafood allergies: a medical myth exposed. J Emerg Med. 2010;39(5), 701-707.
  9. Huang, S. Seafood and Iodine: An Analysis of a Medical Myth. Allergy Asthma Proc. 2005;26(6):468-469.
  10. Scherer K,et al. The role of iodine in hypersensitivity reactions to radio contrast media. Clin Exp Allergy. 2010;40(3):468-475.
  11. Moussa L, et al. Immediate hypersensitivity reactions to iodinated contrast agents used in radiology: a review. J Med Liban. 2012 Jul-Sep;60(3):159-163.
  12. Bottinor W, et al. Adverse Reactions to Iodinated Contrast Media. Int J Angiol. 2013; 22(3):149-154.
  13. Kunze J,et al. Relevance of an iodine allergy to commercial polyvidone-iodine preparations. Z Hautkr. 1983;58(4):255-261.
  14. Van Ketel W, et al. Sensitization to povidone-iodine. Dermatol din 1990;8:107-109.

†Results may vary. Information and statements made are for education purposes and are not intended to replace the advice of your doctor. If you have a severe medical condition or health concern, see your physician.


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