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What is Iodine?
Iodine is a vital micronutrient essential for the synthesis of thyroid hormones, which play a crucial role in regulating growth, development, and metabolism. This article explores the importance of iodine, its sources, the consequences of deficiency and excess, and its broader biological roles. Other names include: Atomic number 53, Cadexomer Iodine, Diatomic Iodine, I2, Iode, Iode de Cadexomer, Iode Diatomique, Iode Moléculaire, Iode Mono-atomique, Iode de Povidone, Iode de Sodium, Iodide, Iodized Salt, Iodure, Iodure de Potassium, Iodure de Potassium en Solution Saturée, Iodure de Sodium, KI, Lugol’s Solution, Molecular Iodine, Monoatomic Iodine, Numéro atomique 53, Periodate de Sodium, Potassium Iodide, Povidone Iodine, Saturated Solution Potassium Iodide, Sel Iodé, Sodium Iodide, Sodium Iodine, Sodium Periodate, Solution de Lugol, SSKI, Yodo.
Importance of Iodine
Iodine is indispensable for the production of thyroid hormones, which are critical for numerous physiological processes. These hormones are particularly important during periods of rapid growth and development, such as pregnancy and early childhood. Inadequate iodine intake can lead to a spectrum of disorders known as iodine deficiency disorders (IDD), which include hypothyroidism, goiter, and severe neurodevelopmental impairments in infants1 4 5.
Sources of Iodine
The primary sources of iodine in the diet include iodized salt, dairy products, seafood, and certain vegetables. Iodine can also be obtained from supplements, which are particularly important in regions where dietary intake is insufficient2 4 6.
Iodine Deficiency
Iodine deficiency remains a significant public health issue globally, affecting approximately 2 billion people. The consequences of iodine deficiency are severe, especially during pregnancy and early childhood, leading to impaired growth, cognitive deficits, and increased infant mortality. Universal salt iodization is a widely recommended strategy to combat iodine deficiency4 5 6 8.
Effects on Pregnancy and Early Development
During pregnancy, iodine requirements increase significantly to support fetal development. Insufficient iodine intake during this period can result in adverse outcomes such as stillbirth, congenital anomalies, and cretinism, a condition characterized by severe intellectual and physical disabilities1 4 5.
Iodine Excess
While iodine deficiency is a major concern, excessive iodine intake can also lead to thyroid dysfunction. In susceptible individuals, such as those with pre-existing thyroid conditions, excessive iodine can cause hypothyroidism or hyperthyroidism. The body’s ability to tolerate high iodine levels is generally robust due to homeostatic mechanisms, but certain populations remain at risk2 4.
Broader Biological Roles
Beyond its role in thyroid hormone synthesis, iodine has other significant biological functions. It acts as an antioxidant, scavenging reactive oxygen species (ROS), and has antimicrobial properties. Additionally, iodine has been shown to have antineoplastic effects, potentially inhibiting cancer progression3 7.
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Uses of Iodine
Nutritional and Health Uses
Thyroid Function and Cognitive Development: Iodine is essential for the metabolism of the thyroid and the development of cognitive abilities in humans. It helps in the biosynthesis of thyroid hormones, which regulate growth, development, and metabolism1 4 5.
Goiter Prevention: Historically, iodine has been used to prevent and treat goiter, an enlargement of the thyroid gland. The use of iodized salt has been effective in preventing simple endemic goiter9 10.
Pregnancy and Postpartum: Iodine supplementation during preconception, pregnancy, and postpartum periods helps meet increased iodine needs, preventing iodine deficiency and its consequences4.
Antiseptic and Disinfectant
Antiseptic Properties: Iodine is widely used as an antiseptic for skin, wounds, and mucous surfaces. It is effective against bacteria, viruses, and fungi, and is used for sterilizing surgical instruments and disinfecting drinking water3 7 8.
Povidone-Iodine: This iodine compound is used in various medical applications due to its broad antimicrobial spectrum and excellent local tolerability8.
Agricultural Uses
Biofortification: Iodine is used to biofortify crops, enhancing their growth, environmental adaptation, and stress tolerance. This can contribute to the nutritional intake of iodine in the population1.
Plant Growth and Stress Tolerance: Some studies report beneficial effects of iodine on plant growth and stress tolerance, although results can vary depending on environmental conditions and application methods1.
Industrial and Synthetic Applications
Organic Synthesis: Hypervalent iodine compounds are used in organic synthesis as selective oxidants and environmentally friendly reagents. They are employed in halogenation reactions, various oxidations, rearrangements, and C-C bond-forming reactions6 10.
Environmental Sustainability: Hypervalent iodine compounds offer an environmentally sustainable alternative to heavy metals in chemical transformations6.
Miscellaneous Uses
Water Purification: Iodine is used for the disinfection of drinking water and swimming pool water3.
Animal Feeds and Dyes: Iodine is used in animal feeds and as a component in dyes and inks2.
Photographic Chemicals: Iodine compounds are used in the production of photographic chemicals2.
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Adverse Effects of Iodine
Thyroid Dysfunction from Excess Iodine Intake in Children
Chronic long-term iodine excess in children can lead to increased thyroid volume, goiter, and elevated thyroglobulin levels. The risk of goiter significantly increases at iodine intakes of 250-299 µg/day in younger children and 300-399 µg/day in older children1.
Adverse Effects of Radioactive Iodine (I-131) Therapy
Radioactive iodine therapy for differentiated thyroid carcinoma (DTC) can cause salivary gland dysfunction, lacrimal gland dysfunction, transient gonadal dysfunction, and secondary primary malignancies. These effects are dose-dependent2 6.
Iodine-Induced Thyroid Disorders
Excessive iodine intake can lead to thyroiditis, goiter, hypothyroidism, and hyperthyroidism. Individuals with underlying thyroid conditions are more susceptible to these effects5 7.
Adverse Effects of Iodine Thyroid Blocking (ITB)
ITB, used in radiological or nuclear accidents to prevent thyroid cancer, generally does not cause severe adverse reactions in the general public. However, the evidence base is weak due to the scarcity of studies4.
Short-Term Adverse Effects of High-Dose Radioactive Iodine Therapy
Short-term effects of high-dose radioactive iodine therapy include gastrointestinal issues, salivary dysfunction, and thyroiditis. These effects are generally self-limiting6.
Iodine Toxicity from Various Sources
Exposure to excessive iodine through foods, supplements, and medications can result in thyroiditis, goiter, hypothyroidism, hyperthyroidism, and sensitivity reactions. Some individuals can tolerate high levels of iodine without adverse effects, but others may experience significant issues even at lower doses7.
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🌀What are the adverse effects of iodine?
How has Iodine Improved Patient Outcomes?
Improved Survival in Thyroid Cancer Patients
RAI therapy is associated with improved overall survival in patients with intermediate-risk papillary thyroid cancer (PTC) and high-risk differentiated thyroid carcinoma (DTC)1 2 7 9.
RAI treatment significantly reduces mortality in patients with Hürthle cell carcinoma (HCC) and stage IV DTC, showing a 30% reduction in mortality for HCC and improved 5- and 10-year survival rates for DTC3 7.
Near-total thyroidectomy followed by RAI therapy is beneficial for stage II, III, and IV thyroid cancer patients, contributing to longer overall survival2.
Cognitive and Developmental Benefits
Iodine supplementation in iodine-deficient schoolchildren significantly improves cognitive functions such as information processing, fine motor skills, and visual problem-solving5.
Maternal iodine sufficiency is associated with better birth outcomes, including higher birth weight and reduced risk of small for gestational age (SGA) infants8.
Enhanced Efficacy of RAI Treatment
A low-iodine diet (LID) before RAI treatment increases the efficacy of thyroid remnant ablation and I-131 uptake, potentially improving long-term thyroid cancer outcomes4.
Psychological and Behavioral Interventions
Psychological and behavioral interventions for patients undergoing RAI treatment for differentiated thyroid cancer improve health-related quality of life and mental health, reducing symptoms of depression and anxiety10.
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Iodine Mechanisms of Action
Antithyroid Action
Iodide can block the formation of organically-bound iodine in the thyroid, inhibiting thyroid hormone synthesis1 7.
Excess iodide can induce the Wolff-Chaikoff effect, temporarily halting thyroid hormone production by blocking iodide organification1 8.
Thyroid Hormone Synthesis
Iodine is essential for the biosynthesis of thyroid hormones (THs), which are critical for metabolic regulation and brain development4 10.
Iodine’s role in thyroid hormone production involves its oxidation and incorporation into thyroglobulin3 6.
Cellular and Molecular Effects
Iodine can inhibit thyroid cell proliferation by affecting both cAMP-dependent and cAMP-independent pathways8.
Iodine interacts with cell membrane lipids, potentially altering membrane properties and affecting cellular functions6.
Antioxidant and Antimicrobial Properties
Molecular iodine (I2) acts as an antioxidant, neutralizing free radicals and inducing antioxidant enzyme expression5 10.
Iodine has bactericidal, antiviral, and antifungal properties due to its oxidation to hypoiodite (IO-)10.
Immune Modulation and Antineoplastic Effects
Iodine can modulate immune responses, acting as either an inhibitor or activator depending on the context5.
Iodine has been shown to exert antineoplastic effects, potentially inhibiting cancer cell growth5 10.
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Common Complaints Associated with Iodine Use
Iodine Deficiency and Neurodevelopmental Issues
Severe iodine deficiency during pregnancy is linked to significant neurodevelopmental problems in children, including language delays, behavior problems, and reduced fine motor skills2.
Suboptimal maternal iodine intake is associated with child language delay, externalizing and internalizing behavior problems, and reduced fine motor skills at 3 years of age2.
Transient Increase in Thyroid Disorders with Iodine Introduction
Introduction of iodized salt in regions with chronic iodine deficiency may temporarily increase the incidence of thyroid disorders, although the benefits of addressing iodine deficiency outweigh these risks1.
Iodine Excess and Thyroid Dysfunction
Excessive iodine intake can lead to thyroid dysfunction, including hypothyroidism and hyperthyroidism, particularly in susceptible individuals such as those with pre-existing thyroid conditions, the elderly, fetuses, and neonates3.
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