 Iodine is a constituent of the thyroid hormones thyroxine (T4) and triiodothyronine (T3) and is an essential mineral in human nutrition. Iodine deficiency results in syndromes known as Iodine Deficiency Disorders (IDD), and in the case of extreme deficiency, goiter. Deficiencies of the thyroid hormones have many effects, including thyroid gland enlargement, congenital and developmental defects, poor growth, and mental retardation. Except for rare instances of hypersensitivity to iodine (note that this is not the same as an allergy), humans are remarkably tolerant to high intakes of iodine. However, excessive supplementation (at least 2,000 mcg per day) may cause or exacerbate acne in some individuals. Kelp as a dietary supplement or fast foods containing high levels of iodized salt may deliver sufficient iodine for this adverse effect. Many people who have had allergic reactions to seafood or x-ray solutions may have been told that it is the iodine component that they are allergic to, which is not very probable. The radiology solutions and foods that contain iodine have many other components (allergens) that are more likely to cause these types of reactions. If dietary iodine were truly the cause, one could not eat any foods containing iodine. Since so many foods contain small amounts of iodine it would be very difficult to avoid it completely. Of course, if you did avoid iodine completely, you would be faced with the deficiency problems discussed previously. Some of the foods commonly containing dietary iodine and their iodine content per serving are as follows: dried beans -115 mcg, shrimp – 35 mcg, spinach – 56 mcg, vegetables – 30 mcg, milk – 56 mcg, eggs – 24 mcg, whole grain wheat – 9 mcg; smaller amounts are found in other grains, beef, rice, and even fruits. If you have been told to avoid supplemental iodine because of a medication you are taking or because of a thyroid condition, please discuss the use of dietary supplements containing iodine with your health care provider.
Shellfish allergies are the most common food allergies in adults and among the most common food allergies in children. Approximately 2% of the U.S. population reports an allergy to shellfish.1 Shellfish allergies are usually lifelong. When a person with an allergy to a particular shellfish is exposed to that shellfish, proteins in the shellfish bind to specific IgE antibodies made by the person’s immune system. This triggers the person’s immune defenses, leading to reaction symptoms that can be mild or very severe. There are two groups of shellfish: crustaceans (such as shrimp, prawns, crab and lobster) and mollusks/bivalves (such as clams, mussels, oysters, scallops, octopus, squid, abalone, snail). Allergy to crustaceans is more common than allergy to mollusks, with shrimp being the most common shellfish allergen for both children and adults. Finned fish and shellfish are not closely related. Being allergic to one does not always mean that you must avoid both, though care is needed to prevent cross-contact between fish and shellfish. Discuss this issue in detail with your allergist to make sure the appropriate food restrictions are implemented.
Iodine is a chemical element that humans require in trace amounts for proper growth and development. For adults, the recommended daily allowance is 150 micrograms. Iodine exists naturally in most soils, and is taken up by plants, which in turn are eaten by humans and animals. Most of the human body’s stores of iodine are located in the thyroid gland, which requires it for the synthesis of thyroid hormones. Allergic reactions to iodine usually stem from iodine-based contrast dyes injected to sharpen pictures in medical imaging studies such as x-rays and CT scans. These reactions typically are mild and involve nausea, vomiting, itching, flushing and hives. But in some cases, reactions can be quite severe (anaphylaxis) with swelling of the throat, difficulty breathing, profound low blood pressure, convulsions, and cardiac arrest. If you’ve experienced a severe reaction as a result of the dye used for an imaging study, make sure your physician and the radiologist supervising any future x-rays or scans are fully aware of your history. Strictly speaking, a reaction to an iodine-based dye is not the same thing as an allergy to iodine because it generally doesn’t stem from the same type of immune-system response as a true allergy. Having a reaction to an iodine-based contrast dye is also not the same as an allergy to seafood, which may be rich in iodine. If you’re reacting to shellfish, the iodine it contains is unlikely to be responsible. It is more likely due to distinctive allergens found in these foods. Most people who are allergic to shellfish react to certain proteins these foods contain, not to iodine. You can be allergic to all types of shellfish or only to mollusks (clams, mussels, oysters and scallops as well as limpets, periwinkles, snails [escargot], abalone, squid, cuttlefish and octopus) or to crustaceans (crabs, lobster, crayfish, shrimp and prawns). Each of these two general types of shellfish contains different proteins. There is a small chance (about three percent) that if you’re allergic to seafood, you’ll have a reaction to contrast dye, but this is no more likely to happen than it is among people with other types of food allergies. In general, if you reacted to an iodine-based contrast dye, you should be able to safely eat seafood and other foods high in iodine. If your reaction was to shellfish of some type, you are probably allergic to something other than iodine. And don’t worry about your thyroid. Your body will get the trace amounts of iodine needed to make thyroid hormone from your diet. Andrew Weil, M.D.
Iodine is a nutrient that is essential for thyroid function. Iodine can be found in fish, shellfish, iodine-based contrast agents used in medical imaging (substances taken into your body to enhance images, making them easier to read), and some disinfectant products. In the past, it was believed that people who experienced an allergic reaction to substances containing iodine were allergic to the nutrient. Healthcare providers now believe that the term, “iodine allergy” should no longer be used because it is inaccurate. Iodine is essential for thyroid function, and an allergy to it would be life-threatening. Research shows that iodine is likely not an allergen and that other substances in items also containing iodine are responsible for any hypersensitivity reactions people may have. This article will explain why some people experience allergic reactions to iodine-containing substances and how to manage the symptoms. AsiaVision / Getty Images If you have an allergy to fish or shellfish, you may have been told that you have an iodine allergy. However, hypersensitivity reactions to fish and shellfish are likely caused by the protein tropomyosin, not iodine.
Possible symptoms of a reaction to shellfish include:
Reactions to iodized contrast agents were considered iodine allergies in the past. However, these reactions are likely caused by another component of the contrast. Symptoms of an allergic reaction may include:
If you think you have an intolerance to iodine or experience symptoms, contact your healthcare provider to get tested. Because a true iodine allergy is unlikely, allergic reactions to iodine-containing substances are likely caused by a sensitivity to a different element in the substance. Without iodine in our diets, our thyroid gland would not function and produce thyroid hormones. These hormones are responsible for growth, brain development, bone formation, and energy metabolism. Our bodies do not make iodine, and so we need to obtain it from our diets. Allergies to seafood, contrast agents, and antiseptic agents have all been diagnosed as iodine allergies in the past. Healthcare providers believe that individuals who experience a hypersensitivity reaction to one or more of these substances are reacting to a protein instead of iodine. An allergic reaction can be life-threatening and requires immediate medical treatment. If you develop difficulty breathing, seek care right away. If you have been diagnosed with an iodine allergy in the past, talk with your healthcare provider to determine which substance caused the reaction. If you can remember, tell your provider the exact symptoms you experienced and how long they lasted. To manage a hypersensitivity to contrast agents, let your healthcare team know that you have reacted to this medication in the past. Next time you are in need of an imaging study such as a computed tomography (CT) scan, your provider will discuss a plan with you. Often people with a history of allergic reactions are treated with medications to prevent a reaction before the procedure. It is estimated that out of 100 million CT scans performed each year, only about 1% to 3% of patients experience a hypersensitivity reaction. If you have ever experienced an allergic reaction to seafood, talk with your healthcare provider about the kinds of fish and shellfish to avoid. Individuals with a shellfish allergy should avoid mollusks like clams, mussels, and oysters, as well as crustaceans like crab, lobster, and shrimp. Iodine is naturally found in dairy products and seafood. It is also added to other foods like table salt. Healthcare providers now believe that an iodine allergy is not caused by iodine at all. What was once thought to be an iodine allergy is most likely a hypersensitivity to a protein. A shellfish allergy is believed to be caused by a sensitivity to the protein tropomyosin. An allergy to disinfectants or contrast is believed to be caused by another ingredient in the substances. Talk with your healthcare provider if you have questions about your risk of allergy. Iodine is a vital nutrient that is needed for thyroid function. It is unlikely for an individual to be allergic to iodine because the nutrient is needed to sustain life. Allergies to shellfish are likely caused by a hypersensitivity to the protein tropomyosin, rather than iodine. An allergic reaction is a medical emergency and requires immediate treatment. If you have ever been diagnosed with an iodine allergy in the past, you may be feeling understandably confused. As research evolves and we learn more about allergies and hypersensitivity reactions, most healthcare providers feel confident that a true iodine allergy is unlikely. To better understand your risk, talk with your healthcare provider about any past allergic reactions. Frequently Asked Questions
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What foods to avoid if you are allergic to iodine
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