Iodine is used for a variety of conditions, both in medical diagnosis and as a form of treatment for a number of thyroid conditions. Side effects to iodine are fortunately rare. They may range from mild reactions, known as "iodism," to potentially life-threatening reactions that include anaphylaxis. Individuals who have an iodine allergy should alert their doctor before undergoing any imaging or radiologic procedures to avoid any potentially dangerous effects.
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Sources of Iodine
Iodine is taken up by the thyroid gland to create thyroid hormone, which plays a critical role in maintaining metabolism. These disorders are relatively rare in the developed world. Iodine is given therapeutically in the treatment of iodine deficiency disorders. Large doses of iodine can paradoxically shut down the thyroid gland temporarily, and hence it can be used in some hyperthyroid emergencies. Radioactive iodine is used in the treatment of Grave's disease, an autoimmune disease that can cause thyroid hyperactivity.
Iodine can also be found in a variety of other sources. Contrast agents are used by radiologists in certain diagnostic procedures and may contain free iodine. In addition, Iodine can be found in a number of antiseptics, as well as in iodized salt, bread preservatives and seafood.
Iodine taken orally for thyroid deficiencies is usually safe. Adverse reactions may occur when excess iodine is taken. Side effects include diarrhea, nausea, stomach pain, mild fever and a headache. Iodine can cause a metallic taste in the mouth, numbness or tingling in the hands and feet, and swollen salivary glands. Allergic reactions to iodine are rare but can include hives, difficult breathing and chest tightness. Anaphylatic reactions, in which there is a dangerous fall in blood pressure, difficult breathing and irregular heartbeat, are very rare with iodine therapy.
Radioactive Iodine Therapy
Radioactive iodine therapy is used in the treatment of Grave's disease. The radiation is typically too low to increase the risk of future thyroid cancer. The iodine may cause mild throat pain, swelling of salivary glands, and nausea that can last for several hours. However, use of radioactive iodine can cause a gradual deterioration of thyroid function and lead to hypothyroidism. Women who are pregnant or lactating should not be given radioactive iodine as it may cause thyroid deficiencies in the fetus.
Iodine is used on computerized tomogoraphy, or CT, studies as a contrast agent to sharpen images. Iodine used in radiology can provoke a variety of reactions. While the symptoms resemble those of allergies, they do not directly involve the immune system and hence are not allergic. Mild reactions consist of skin hives, which can manifest as red, itchy welts over the skin that can vary in size and shape over time. They can last for several days. Angioedema is a reaction of the tissues below the skin and can cause puffiness of the face and of the larynx, which can make breathing difficult. More severe reactions can cause asthmatic airway constriction or even a systemic response known as anaphylaxis.