Iodine (Potassium Iodide/Kelp)
1. Introduction – What is the product, chemical/botanical basics, mechanism of action
Iodine is a trace element essential for human health, primarily known for its critical role in the synthesis of thyroid hormones, thyroxine (T4) and triiodothyronine (T3) [1]. These hormones are vital regulators of numerous biochemical reactions, including protein synthesis, enzymatic activity, and metabolic rate, and are indispensable for proper skeletal and central nervous system development in fetuses and infants [1, 2].
Iodine is not produced by the body and must be obtained through diet or supplementation. In supplements, it is commonly found in the form of potassium iodide (KI) or sodium iodide. When sourced naturally, it is often derived from kelp (a type of brown seaweed, Laminariales), which is one of the richest natural sources of the element [3].
Chemical/Botanical Basics
- Chemical Form: Iodine rarely exists as the element (I₂) but rather as the reduced salt, iodide (I⁻), or as iodate (IO₃⁻) [2]. Potassium iodide (KI) is a stable, white crystalline salt that is easily absorbed by the body [4].
- Botanical Source (Kelp): Kelp is a large, brown algae belonging to the order Laminariales. The iodine content in kelp and other seaweeds can vary dramatically depending on the species, harvest location, and processing [3].
Mechanism of Action
The primary mechanism of action for iodine is its incorporation into the thyroid hormones.
- Uptake: Iodide (I⁻) from the circulation is actively concentrated by the thyroid gland via the sodium-iodide symporter (NIS). Iodate is reduced in the gastrointestinal tract and absorbed as iodide [2].
- Organification: Within the thyroid, iodide is oxidized and then incorporated into tyrosine residues on the thyroglobulin protein.
- Hormone Synthesis: This process forms monoiodotyrosine (MIT) and diiodotyrosine (DIT), which are then coupled to form the active thyroid hormones, T4 (four iodine atoms) and T3 (three iodine atoms) [1].
- Regulation: Thyroid-stimulating hormone (TSH), secreted by the pituitary gland, regulates this process. Insufficient iodine causes TSH levels to remain elevated, leading to goiter as the thyroid attempts to trap more iodine [2].
2. Chemical Composition/Key Bioactive Roles
The key bioactive component of the supplement is the iodide ion (I⁻), which is the substrate for thyroid hormone production.
| Bioactive Compound | Source in Supplement | Key Role in the Body |
|---|---|---|
| Iodide (I⁻) | Potassium Iodide, Kelp | Essential substrate for the synthesis of thyroid hormones (T3 and T4) [1]. |
| Thyroxine (T4) Precursor | Iodide | Regulates metabolic rate, protein synthesis, and enzymatic activity [1]. |
| Triiodothyronine (T3) Precursor | Iodide | The most active thyroid hormone, crucial for growth and development [1]. |
| Potassium (K⁺) | Potassium Iodide | An essential electrolyte; maintains cell membrane potential and fluid balance. |
| Other Trace Minerals | Kelp | Kelp is a source of other minerals like iron, manganese, and zinc, though iodine is the primary focus [3]. |
3. Health Benefits
Iodine’s health benefits are overwhelmingly linked to its role in thyroid function and the prevention of Iodine Deficiency Disorders (IDD).
Fetal and Infant Neurodevelopment
Iodine sufficiency during pregnancy is paramount for the proper development of the fetal brain and nervous system [5]. The fetus relies entirely on maternal T4 during early pregnancy. Studies have shown that even mild to moderate maternal iodine insufficiency can subtly affect fetal development, potentially leading to lower verbal IQ scores in children [5, 6].
- Evidence: A meta-analysis of over 6,000 mother-child pairs found that lower maternal iodine status in the first trimester was associated with lower verbal IQ in children aged 1.5 to 8 years [6].
- Dosage Context: To meet the increased demands, the RDA for pregnant women is 220 mcg/day, and for lactating women, it is 290 mcg/day [2].
Cognitive Function in Children
Severe iodine deficiency is a known cause of preventable intellectual disability worldwide [7]. Correcting even mild iodine deficiency in children has been shown to improve cognitive measures.
- Evidence: A randomized, placebo-controlled study in New Zealand children (median urinary iodine concentration 63 mcg/L, indicating mild deficiency) found that supplementation with 150 mcg/day of iodine for 28 weeks significantly improved measures of perceptual reasoning and overall cognitive score compared to placebo [8].
Protection Against Radiation-Induced Thyroid Cancer
Potassium iodide (KI) is approved by the FDA as a thyroid-blocking agent in the event of a nuclear emergency involving the release of radioactive iodine [9].
- Mechanism: When taken in a high, pharmacological dose (typically 16 mg to 130 mg of potassium iodide, depending on age), the stable iodine saturates the thyroid gland, preventing the uptake of harmful radioactive iodine [9]. This is a medical intervention, not a daily supplement use.
Fibrocystic Breast Disease
Some limited research suggests that iodine supplementation may help alleviate symptoms of fibrocystic breast disease, a benign condition characterized by painful, lumpy breasts.
- Evidence: A randomized, double-blind, placebo-controlled clinical trial found that women receiving 3,000 mcg (3 mg) or 6,000 mcg (6 mg) of iodine per day for five months reported a significant decrease in breast pain, tenderness, and nodularity compared with those receiving placebo [10]. Note: These doses are several times higher than the Tolerable Upper Intake Level (UL) and should only be used under medical supervision [2].
4. Dosage and Usage
Recommended Daily Allowances (RDAs)
The Recommended Dietary Allowance (RDA) for iodine is expressed in micrograms (mcg) [2].
| Age Group | RDA (mcg/day) |
|---|---|
| Children 1–8 years | 90 mcg |
| Children 9–13 years | 120 mcg |
| Adolescents 14–18 years | 150 mcg |
| Adults (19+ years) | 150 mcg |
| Pregnant Women | 220 mcg |
| Lactating Women | 290 mcg |
Food Sources
The iodine content of food is highly variable, but the best sources include [3]:
- Seaweed (Kelp, Nori, Wakame): Kelp is exceptionally high, with concentrations ranging from 16 mcg/g to nearly 3,000 mcg/g in commercially available products.
- Seafood: Cod, tuna, and shellfish (e.g., oysters, shrimp). A 3-ounce serving of baked cod provides about 146 mcg [3].
- Dairy Products: Milk and yogurt (iodine content is variable).
- Iodized Salt: ¼ teaspoon of iodized table salt provides about 78 mcg [3].
5. Safety and Precautions
Tolerable Upper Intake Level (UL)
The FNB has established a Tolerable Upper Intake Level (UL) for iodine, which is the maximum daily intake unlikely to cause adverse health effects [2].
| Age Group | UL (mcg/day) |
|---|---|
| Children 1–3 years | 200 mcg |
| Children 4–8 years | 300 mcg |
| Children 9–13 years | 600 mcg |
| Adolescents 14–18 years | 900 mcg |
| Adults (19+ years) | 1,100 mcg (1.1 mg) |
Serious Safety Warnings (Excessive Intake)
WARNING: High intakes of iodine can paradoxically cause the same symptoms as iodine deficiency, including goiter, elevated TSH levels, and hypothyroidism [11]. In susceptible individuals (e.g., those with pre-existing autoimmune thyroid disease or long-standing iodine deficiency), excess iodine can inhibit thyroid hormone synthesis. Iodine-induced hyperthyroidism can also occur [11].
- Acute Poisoning: Rare, but can occur with doses of many grams. Symptoms include burning of the mouth, throat, and stomach; fever; abdominal pain; nausea; vomiting; diarrhea; weak pulse; and coma [11].
- Kelp Supplements: Due to the high variability of iodine content in kelp, some kelp supplements can provide extremely high, potentially unsafe doses of iodine, exceeding the UL [3]. Supplement users should verify the exact iodine content.
Contraindications and Drug Interactions
Individuals taking certain medications should consult a healthcare provider before supplementing with iodine [12].
| Medication Class | Interaction | Warning |
|---|---|---|
| Antithyroid Medications (e.g., Methimazole) | Additive effect. High doses of iodine can increase the risk of hypothyroidism when combined with these drugs. | Increased risk of hypothyroidism. |
| Angiotensin-Converting Enzyme (ACE) Inhibitors (e.g., Lisinopril, Benazepril) | Potassium iodide can increase the risk of hyperkalemia (elevated blood potassium levels). | Increased risk of hyperkalemia. |
| Potassium-Sparing Diuretics (e.g., Spironolactone, Amiloride) | Potassium iodide can increase the risk of hyperkalemia. | Increased risk of hyperkalemia. |
6. References
[1] National Research Council, Committee to Assess the Health Implications of Perchlorate Ingestion. Health Implications of Perchlorate Ingestion. Washington, DC: The National Academies Press, 2005.[2] Institute of Medicine, Food and Nutrition Board. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. Washington, DC: National Academy Press, 2001.[3] USDA, FDA, and ODS-NIH Database for the Iodine Content of Common Foods Release 4.0. 2024.[4] Aquaron R, Delange F, Marchal P, Lognoné V, Ninane L. Bioavailability of seaweed iodine in human beings. Cell Mol Biol (Noisy-le-grand). 2002 Jul;48(5):563-569. [PubMed abstract] [5] Zimmermann MB. Iodine deficiency. Endocr Rev. 2009 Jun;30(4):376-408. [PubMed abstract] [6] Levie D, Korevaar TIM, Bath SC, Murcia M, Dineva M, Llop S, Espada M, van Herwaarden AE, de Rijke YB, Ibarluzea JM, Sunyer J, Tiemeier H, Rayman MP, Guxens M, Peeters RP. Association of maternal iodine status with child IQ: A meta-analysis of individual participant data. J Clin Endocrinol Metab 2019;104:5957-67. [PubMed abstract] [7] Zimmermann MB, Jooste PL, Pandav CS. Iodine-deficiency disorders. Lancet. 2008 Oct 4;372(9645):1251-1262. [PubMed abstract] [8] Gordon RC, Rose MC, Skeaff SA, Gray AR, Morgan KM, Ruffman T. Iodine supplementation improves cognition in mildly iodine-deficient children. Am J Clin Nutr. 2009 Nov;90(5):1264-1271. [PubMed abstract] [9] Center for Drug Evaluation and Research, Food and Drug Administration. Guidance. Potassium iodide as a thyroid blocking agent in radiation emergencies. December 2001.[10] Kessler JH. The effect of supraphysiologic levels of iodine on patients with cyclic mastalgia. Breast J. 2004 Jul-Aug;10(4):328-336. [PubMed abstract] [11] Pennington JA. A review of iodine toxicity reports. J Am Diet Assoc. 1990 Nov;90(11):1571-1581. [PubMed abstract] [12] Natural Medicines Comprehensive Database. Iodine. Accessed 10/13/2009.Full Reference List with Clickable URLs
[1] National Research Council, Committee to Assess the Health Implications of Perchlorate Ingestion. Health Implications of Perchlorate Ingestion. Washington, DC: The National Academies Press, 2005. (No public URL available for this book) [2] Institute of Medicine, Food and Nutrition Board. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. Washington, DC: National Academy Press, 2001. (No public URL available for this book) [3] USDA, FDA, and ODS-NIH Database for the Iodine Content of Common Foods Release 4.0. 2024. (No public URL available for this database) [4] Aquaron R, Delange F, Marchal P, Lognoné V, Ninane L. Bioavailability of seaweed iodine in human beings. Cell Mol Biol (Noisy-le-grand). 2002 Jul;48(5):563-569. [PubMed abstract]. URL: https://pubmed.ncbi.nlm.nih.gov/12478546/ [5] Zimmermann MB. Iodine deficiency. Endocr Rev. 2009 Jun;30(4):376-408. [PubMed abstract]. URL: https://pubmed.ncbi.nlm.nih.gov/19460986/ [6] Levie D, Korevaar TIM, Bath SC, et al. Association of maternal iodine status with child IQ: A meta-analysis of individual participant data. J Clin Endocrinol Metab. 2019;104:5957-67. [PubMed abstract]. URL: https://pubmed.ncbi.nlm.nih.gov/31338487/ [7] Zimmermann MB, Jooste PL, Pandav CS. Iodine-deficiency disorders. Lancet. 2008 Oct 4;372(9645):1251-1262. [PubMed abstract]. URL: https://pubmed.ncbi.nlm.nih.gov/18848365/ [8] Gordon RC, Rose MC, Skeaff SA, et al. Iodine supplementation improves cognition in mildly iodine-deficient children. Am J Clin Nutr. 2009 Nov;90(5):1264-1271. [PubMed abstract]. URL: https://pubmed.ncbi.nlm.nih.gov/19797087/ [9] Center for Drug Evaluation and Research, Food and Drug Administration. Guidance. Potassium iodide as a thyroid blocking agent in radiation emergencies. December 2001. URL: https://www.fda.gov/regulatory-information/search-fda-guidance-documents/potassium-iodide-thyroid-blocking-agent-radiation-emergencies [10] Kessler JH. The effect of supraphysiologic levels of iodine on patients with cyclic mastalgia. Breast J. 2004 Jul-Aug;10(4):328-336. [PubMed abstract]. URL: https://pubmed.ncbi.nlm.nih.gov/15239792/ [11] Pennington JA. A review of iodine toxicity reports. J Am Diet Assoc. 1990 Nov;90(11):1571-1581. [PubMed abstract]. URL: https://pubmed.ncbi.nlm.nih.gov/2229598/ [12] Natural Medicines Comprehensive Database. Iodine. Accessed 10/13/2009. (No public URL available for this database)Note on References 1, 2, 3, and 12: The NIH ODS fact sheet cited several books and proprietary databases (like the IOM/FNB DRIs and Natural Medicines Comprehensive Database) that do not have direct, publicly accessible, clickable URLs. For the purpose of meeting the “at least 3 scientific sources with full URLs” requirement, I have ensured that the other 8 references are scientific papers with full PubMed or FDA URLs. The core information is validated by the NIH ODS fact sheet itself.
