Iodine
Many women lack sufficient iodine during pregnancy and lactation, and prenatal supplements often lack sufficient amounts.
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Critical for fetal development, [1,2] including brain, [1,2] nervous system, [1,2] and skeletal formation [1]
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Necessary for proper thyroid hormone production, which affects growth and metabolism, temperature regulation, and reproduction [1,2]
How it works
Recommended daily amount
The iodine content of foods can vary due to the amount found in the soil, water, and animal feed. Thus, plant foods may or may not have iodine depending on where they are grown and other factors. [1-3]
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Iodized salt
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Seaweed (e.g., kombu, kelp, wakame, nori)
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Supplements, including some multivitamins
Animal sources: primarily seafood. Dairy and eggs may have some iodine due to animal feed supplementation and sanitizing solutions used in processing dairy in the U.S. [1]
Sources of nutrient
Daily upper limits
Examples of nutrient-rich foods
Typically, greater than 90% of iodine from most food sources is absorbed,[2,3] and supplements and fortified salt are almost completely absorbed. [1,2]
High intake of foods with goitrogens (e.g., cassava, soy, cabbage, millet) has the potential to inhibit iodine transfer to the thyroid gland; however, this is typically not a concern in individuals with sufficient iodine intake and those consuming a variety of foods. [1,2]
Bioavailability
Urinary iodine reflects recent (days) dietary intake. [1,2] Multiple urine spot measures or 24-hour urinary iodine measures are more accurate for individuals than one single measure. [1,7]
The following values are taken from population values of median concentrations of urinary iodine for adequate iodine status: [1,7]
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Children and adults: 100 – 199 mcg/L (excessive [3,7] > 300 mcg/L)
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Pregnant: 150 – 249 mcg/L (excessive [3,7] ≥ 500 mcg/L)
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Lactating: > 100 mcg/L (the lower levels are due to iodine excretion into breast milk [7])
24-hour urinary iodine can estimate intake by the following formula: urinary iodine (mcg/L) x 0.0235 x weight (kg) = daily iodine intake. [2]
Thyroid size, either by palpitation (each lobe should be no larger than the terminal phalanx of the patient’s thumb) or more precisely, by ultrasound, can be used to estimate the presence of iodine deficiency. [2] Reference values related to body surface area and age exist for school-age children in the U.S., Europe, and several other countries. [2]
Serum TSH reflects thyroid hormone production that requires iodine. [2] Although many countries use TSH in newborns to estimate population iodine status, serum TSH in older children and adults is not a sensitive indicator of iodine status and can be in the normal range with iodine deficiency. [7] T3 and T4 are relatively insensitive and unreliable measures of iodine status. [2]
Measures of Adequate Status
Pregnant women who do not consume good sources of iodine (e.g., iodized salt) - It is critical that a source of iodine be in the diet for proper fetal development. Lack of iodine can result in impaired mental and physical development and birth defects. [1,3]
Breastfed babies of mothers with insufficient iodine intake (maternal diet affects milk concentrations). Studies in the U.S. found nearly 50% of women had insufficient iodine concentrations in breast milk. [1]
Persons consuming excessive amounts of goitrogenic foods (e.g., cassava, soy, millet, cabbage) AND do not consume sufficient iodine. [1]
Persons who do not regularly use iodized table salt or consume rich sources of iodine (e.g., seafood) [6]
Smokers (due to cyanide in tobacco) [7]
Populations at risk for deficiency
Deficiency signs and symptoms
Hypothyroidism [1,2]
Increased TSH [2]
Goiter [1,2]
Impaired child development, stunted growth [1,2]
Delayed sexual maturation [1]
Impaired mental function [1,2]
Stillbirth, miscarriage, birth defects, endemic cretinism [1]
Increased risk of thyroid cancer with chronic deficiency [1,2]
For diets that lack sufficient iodine, especially in countries that lack iodized salt or are at risk for iodine deficiency (e.g., many European countries), the following should be considered:
Pregnant and lactating women - At least 150 mcg per day of iodine as part of prenatal/ multivitamin supplements; [8] high-dose iodine supplements should be avoided,[9] and avoid more than 1100 mcg/d of total iodine from food & supplements (≤18 years old should avoid ≥ 900 mcg/d). [2,9]
Infants under 6 months – Iodine should only come from breast milk or formula. Infants 7 – 12 months – Iodine should come from breast milk or infant formula, although some countries recommend 50 mcg/d for infants consuming home-made food [10]
Children one year and older - Iodine supplement may be indicated only when iodine intake from foods is insufficient. Families should be advised about the potential harms of excessive iodine intake.
Prevention of Deficiency
The content provided is for informational purposes only and may not be an exhaustive list of potential interactions.
Anti-thyroid medications (e.g., methimazole, [1,7] propylthiouracil, [7] carbimazole [7]) and high doses of iodine can have an additive effect and could cause hypothyroidism. [1,7]
Amiodarone contains high levels of iodine and may affect thyroid function. [7]
ACE inhibitors (e.g., Lisinopril) and potassium-sparing diuretics (e.g., spironolactone) with potassium iodide (found in supplements, iodized salt substitutes) can increase the risk of hyperkalemia. [1]
Long-term use of lithium may increase the risk of hypothyroidism. [7]
Pharmaceutical doses of potassium iodide may decrease the anticoagulant effect of warfarin. [7]
Potential drug-nutrient interactions
Thyroiditis [2]
Hypothyroidism [1,2]
Hyperthyroidism [2]
Sensitivity reactions [2]
Elevated TSH [1,2] Goiter [1,2]
Increased risk of thyroid cancers [1,2]
Acute iodine poisoning symptoms include: [1,2]
Burning of the mouth, throat, stomach
Fever Abdominal pain
Nausea, vomiting, diarrhea
Weak pulse
Coma
Toxicity signs and symptoms
Heading 3
Notes
Many supplements, including prenatal vitamins, do not contain adequate iodine. [6]
Adverse effects of using iodine supplements have been documented, [1,2] including increased risk of hyperthyrotropinemia in pregnant women using iodine supplements. [1]
Breast milk iodine concentrations depend on maternal intake; thus, exclusively breastfed infants rely on maternal iodine sufficiency for optimal development. [1]
Switching to iodized salt (but not adding extra salt to the diet) is a feasible source of iodine, particularly for those who do not regularly consume dairy, eggs, and seafood. [6] Approximately half a teaspoon of iodized salt can provide 100% of the recommended daily amounts of iodine for many age groups but may exceed sodium requirements for younger children. [1,4,5]
Most processed foods in the U.S. do not use iodized salt; if they do, they must be listed with the nutrition facts label.[1]
Deficiencies in selenium, vitamin A, or iron can exacerbate iodine deficiency. [2,7]
Iodine is absorbed in the stomach and duodenum. [1] Iodine is primarily cleared by the kidney and thyroid. [2,3] Iodine uptake by the thyroid varies by intake, [3] and 90% of ingested iodine is ultimately excreted in urine. [1,2] Iodine also gets recycled in the body. [2]
Notes
1. Iodine. Fact Sheet for Health Professionals. Office of Dietary Supplements. National Institutes of Health. Updated Mar 2020. Accessed Nov 2020. https://ods.od.nih.gov/factsheets/Iodine-HealthProfessional/.
2. Institute of Medicine 2001. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. Washington, DC: The National Academies Press. https://doi.org/10.17226/10026.
3. Zimmerman M, Trumbo PR. Iodine. Adv. Nutr.2013; 4: 262–264.
4. FoodData Central Database. United States Department of Agriculture. Accessed Oct 2021. https://fdc.nal.usda.gov.
5. Iodine. USDA, FDA, ODS-NIH Iodine Database Release 1.0. https://www.ars.usda.gov/ARSUSERFILES/80400535/DATA/IODINE/IODINE%20DATABASE_DOCUMENTATION.PDF
6. U.S. Department of Agriculture and U.S. Department of Health and Human Services. Dietary Guidelines for Americans, 2020-2025. 9th Edition. December 2020. Available at https://DietaryGuidelines.gov.
7. Iodine. Linus Pauling Institute Micronutrient Information Center, Oregon State University. Updated August 2015. Accessed Nov 2020. https://lpi.oregonstate.edu/mic/minerals/iodine
8. Leung AM, Pearce EN, Braverman LE, Stagnaro-Green A. AAP recommendations on iodine nutrition during pregnancy and lactation. Pediatrics. 2014 Oct;134(4):e1282.
9. Leung AM, Braverman LE. Consequences of excess iodine. Nat Rev Endocrinol. 2014 Mar;10(3):136-42. doi: 10.1038/nrendo.2013.251. Epub 2013 Dec 17.
10. Remer T, Johner SA, Gärtner R, et al. Ein Risiko für die Kognitive Entwicklung [Iodine deficiency in infancy - a risk for cognitive development]. Dtsch Med Wochenschr. 2010 Aug;135(31-32):1551-6. German. doi: 10.1055/s-0030-1262446. Epub 2010 Jul 27. PMID: 20665419.