Are Iodine Supplements Needed?
Posted:
2025-07-02
What’s happening?
Consumer eating habits and resultant diet quality has changed over the years (1,2). Individuals are eating away from home more often and are eating more processed and ultra-processed foods which contain lower levels of iodized salt. At the same time, consumers are decreasing their intake of iodized table salt (a major source of iodine) and opting for non-iodized salt options including kosher, Himalayan pink or sea salt that contain little to no iodine (1,3). Concerns have been raised that iodine supplements may be needed to prevent mild to moderate iodine deficiencies that have been increasing (1). Just under 10 years ago, the PEN Team wrote a short Trending Topic on Iodine Deficiency in the UK, so we thought it was a good time to review this topic.
About iodine
Iodine is a component of thyroid hormones, which regulate various enzymes and metabolic processes, including protein synthesis important for growth and development (4). It is an essential nutrient that is needed through food or supplements: food sources include seaweed, seafood, eggs and dairy (from cows receiving iodine feed supplements and sanitizing agents); fortification (added iodine to salt); or supplements (4,5). Soil is often low in iodine, failing to provide a source of iodine within crops and fruits grown in these soils. During pregnancy and lactation a higher iodine intake is needed (4-6). With both iodine deficiencies and excess iodine resulting in similar symptoms, including goitre and hypothyroidism (4), ensuring individuals get the right amounts of iodine is important. To note, not all goitres are related to iodine deficiency or excess (7).
What does the evidence say?
A 2022 Canadian study (Prospective Urban and Rural Epidemiology (PURE) study) looked at the prevalence and risk factors associated with iodine deficiency in adults (n=800, median age of 61 years) based on the analysis of 24 h urine iodine concentration (UIC) (8). The authors found that overall the Canadian adult cohort had adequate iodine status as reflected by a median UIC of 111 mcg/L; however, 11.9% of the population with UIC <50 mcg/L were grouped as having moderate to severe iodine deficiency, suggesting that greater public awareness of iodine nutrition in a healthy diet may be warranted.
A 2020 systematic review and meta-analysis of 37 studies (10 randomized controlled trials (RCT), 4 non-RCT interventions and 23 observational studies; n=183,814) found that there was not enough high quality evidence to support iodine supplementation in pregnant women with mild to moderate iodine deficiency for the prevention or improvement of maternal thyroid function (measured by thyroid-stimulating hormone (TSH), free thyroxine, thyroglobulin or thyroid volume), infant thyroid function (measured by TSH or free thyroxine) or child neurological development (cognitive, motor or behavioural) (9). Most included studies were conducted in high income countries and baseline UIC ranged from 35 to 197 mcg/L.
Of note, the daily recommended dietary allowance for iodine is (4.5): birth to 6 months 110 mcg (adequate intakes); 7 to 12 months 130 mcg (adequate intakes); children 1 to 8 years 90 mcg; children 9–13 years 120 mcg; over 14 years including adults 150 mcg; and in pregnancy 220 mcg and lactation 290 mcg. An example of food sources of iodine are: seafood (i.e. 75 g cooked salmon provides 8 mcg); seaweed (i.e. 30 mL of nori provides 11 mcg); and eggs (1 egg provides 31 mcg) (4,10).
The bottom line
In general, healthy individuals appear to be meeting daily iodine requirements and do not need added supplementation. Dietitians are encouraged to promote healthy eating guidelines that include eating a variety of foods that contain natural iodine.
Other considerations include:
Adequate amounts of iodine are needed during pregnancy and lactation for the baby’s brain and nervous system development (4). There is not enough high-quality evidence to recommend iodine supplementation during pregnancy to prevent or treat low maternal or infant biomarkers of thyroid function. Similarly, iodine supplementation does not appear to affect child neurological development (cognitive, motor or behavioural) (11). Dietitians are encouraged to promote adequate intake through healthy eating guidelines.
Australia and the American Thyroid Association recommend that pregnant women take a multivitamin supplement that contains iodine (150 mcg/day) (11). The American Thyroid Association and the American Association of Clinical Endocrinologists (ACCE) 2012 guidelines for the treatment of hypothyroidism do not recommend the use of iodine supplements consisting of kelp or other seaweed-based products to manage iodine deficiency in pregnant women due to variability in iodine content (11).
For individuals with hypothyroidism who are pregnant and taking thyroid medication, iodine supplements are not needed as the medication provides the hormone needed (12).
For individuals with hypothyroidism who are taking thyroid medications, iodine supplementation, including kelp supplementation, is not recommended due to the risk of worsening thyroid function and the lack of clinical benefit (13).
For individuals who follow a vegetarian diet, seaweed, eggs and dairy are sources of iodine (4). Vegans who do not consume enough iodine from seaweed, such as nori or kelp and iodine-fortified plant-based dairy alternatives (check the labels) may need to discuss their need for a supplement with a dietitian.
See Additional Content:
Australia
Iodine (Betterhealth Channel)
Iodine and Vegetarian Diets
Canada
Food Sources of Iodine
Healthy Eating Guidelines for Vegans (Adults)
United Kingdom
BDA Food Fact Sheet: Iodine
BDA Food Fact Sheet: Vegetarian, Vegan and Plant-Based Diet
References:
Noon J. Iodine in table salt: how a public health victory is becoming a victim of its own success. CBC News. 2025-02-15. Available from: https://www.cbc.ca/news/health/iodine-deficiency-second-opinion-1.7459781
Guthrie J. Food consumption and nutrient intake trends emerge over past four decades. 2024-08-24. Available from: https://www.ers.usda.gov/amber-waves/2024/august/food-consumption-and-nutrient-intake-trends-emerge-over-past-four-decades
Dietitians of Canada. PEN. Q: What dietary patterns may affect blood pressure in individuals with or at risk for hypertension? Last Updated: 2023-02-09. Available from: https://www.pennutrition.com/KnowledgePathway.aspx?kpid=674&pqcatid=146&pqid=29539
National Institutes of Health. Iodine - Fact Sheet for Professionals. (Nov 5, 2024) Available from: https://ods.od.nih.gov/factsheets/Iodine-HealthProfessional/
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. Available from: https://nap.nationalacademies.org/read/10026/chapter/2
World Health Organization. United Nations Children’s Fund & International Council for the control of iodine deficiency disorders. Assessment of iodine deficiency disorders and monitoring their elimination. 3rd ed. Geneva, Switzerland: WHO, 2007. Available from: https://iris.who.int/handle/10665/43781
Mayo Clinic. Goitre. Apr 29, 2025. Available from: https://www.mayoclinic.org/diseases-conditions/goiter/symptoms-causes/syc-20351829
Mathiaparanam S, Nori de Macedo A, Mente A, Poirier P, Lear SA, Wielgosz A, Teo KK, Yusuf S, Britz-Mckibbin P. The prevalence and risk factors associated with iodine deficiency in Canadian Adults. Nutrients. 2022 Jun 21;14(13):2570. doi: 10.3390/nu14132570. PMID: 35807751; PMCID: PMC9268597. Abstract available from: https://pubmed.ncbi.nlm.nih.gov/35807751/
Dineva M, Fishpool H, Rayman MP, Mendis J, Bath SC. Systematic review and meta-analysis of the effects of iodine supplementation on thyroid function and child neurodevelopment in mildly-to-moderately iodine-deficient pregnant women. Am J Clin Nutr. 2020 Aug 1;112(2):389-412. doi: 10.1093/ajcn/nqaa071. PMID: 32320029. Abstract available from: https://pubmed.ncbi.nlm.nih.gov/32320029/
United States Department of Agriculture, Methods and Application of Food Composition Laboratory: Beltsville, MD. USDA, FDA and ODS-NIH database for the iodine content of common foods. October 2024. Available from: https://www.ars.usda.gov/ARSUserFiles/80400535/Data/Iodine/IODINE_DATABASE_RELEASE_4_PER_SERVING.pdf
Dietitians of Canada. PEN. Q: What are the indications for the use of vitamin/mineral supplements during pregnancy? Updated: 2021-11-30. Available from: https://www.pennutrition.com/KnowledgePathway.aspx?kpid=3043&pqcatid=146&pqid=724
Dietitians of Canada. PEN. Q: For pregnant women with hypothyroidism taking thyroid medication, does iodine supplementation improve thyroid function? Updated: 2022-01-13. Available from: https://www.pennutrition.com/KnowledgePathway.aspx?kpid=6927&pqcatid=146&pqid=28820
Dietitians of Canada. PEN: Q: For individuals with hypothyroidism taking thyroid medication, does iodine supplementation improve thyroid function? Updated: 2021-02-05. Available from: https://www.pennutrition.com/KnowledgePathway.aspx?kpid=6927&pqcatid=146&pqid=28649
