Home Ingredients Iodine
Thyroid Health

Iodine

Evidence Level
Very Strong
1 Clinical Trial
4 Documented Benefits
5/5 Evidence Score

Iodine is an essential trace mineral that the thyroid gland uses to make thyroid hormones, which regulate metabolism, growth, and development throughout the body. Adequate iodine is especially critical during pregnancy for healthy fetal brain development. Most people in regions using iodized salt get enough, and seafood and dairy are good sources, so routine supplements provide modest amounts (around 150 mcg). Both too little and too much iodine can disrupt the thyroid, so very high-dose products such as some kelp supplements should be used cautiously. People with thyroid conditions should discuss iodine intake with their doctor before supplementing.

Studied Dose 150 mcg/day (adults RDA); 220–290 mcg/day (pregnancy/lactation); upper limit 1,100 mcg/day
Active Compound Potassium Iodide / Sodium Iodide / Kelp (organic iodine)
Deficiency information View details

Iodine deficiency was once endemic in the US Midwest 'goiter belt' but largely eliminated by salt iodization beginning in 1924. It remains one of the world's most common preventable causes of intellectual disability — severe deficiency during pregnancy causes irreversible brain damage and cretinism in offspring. Mild-to-moderate iodine deficiency is re-emerging in some US groups due to reduced iodized salt use and increased processed food consumption.

Common symptoms

  • Enlarged thyroid (goiter) — visible swelling at the front of the neck
  • Fatigue and lethargy
  • Weight gain, cold intolerance
  • Dry skin, brittle hair, hair loss
  • Constipation
  • Memory or concentration problems, depression
  • Heavy or irregular menstrual periods
  • Slowed heart rate (hypothyroid symptoms)
  • In severe maternal deficiency: miscarriage, stillbirth, intellectual disability or cretinism in offspring (IRREVERSIBLE)

At-risk groups

  • Pregnant and breastfeeding women (requirements increase to 220-290 µg/day; ATA recommends 150 µg supplemental)
  • Women planning pregnancy (fetal brain development depends on adequate iodine from week 1)
  • People avoiding iodized salt (sea salt and kosher salt typically aren't iodized)
  • People on strict vegan diets (limited dairy and fish, both major sources)
  • People avoiding dairy (lactose intolerance, dairy allergy) without replacement sources
  • People in regions with selenium-deficient soils (selenium needed for thyroid hormone metabolism)
  • People consuming large amounts of goitrogenic foods (raw cruciferous vegetables, soy) without adequate iodine
When to see a doctor: Visible neck swelling, persistent fatigue with cold intolerance, or unexplained weight gain warrants TSH and possibly free T4 testing. CRITICAL: anyone planning pregnancy or in early pregnancy should ensure adequate iodine — most prenatal vitamins contain 150 µg, but check the label. Severe maternal iodine deficiency damages the fetal brain in the first trimester, often before pregnancy is recognized. Note: excessive iodine (especially from kelp supplements) can also disrupt thyroid function — moderation matters.
Explore related deficiencies →
Sources: NIH ODS — Iodine Health Professional Fact Sheet · Iodine Deficiency in Pregnancy (PMC3637994)

Benefits

Thyroid hormone production

Iodine is incorporated into thyroxine (T4) and triiodothyronine (T3) by the thyroid gland. These hormones regulate basal metabolic rate, protein synthesis, and nearly every organ system in the body.

Supported by Trial 1

Metabolic regulation

Thyroid hormones control metabolic rate, body temperature, heart rate, and energy utilization. Adequate iodine prevents hypothyroidism-related fatigue, weight gain, and cold intolerance.

Supported by Trial 1

Fetal brain development

Iodine is critical during the first trimester when the fetal thyroid is not yet functional. Severe deficiency causes cretinism; mild deficiency impairs IQ and cognitive development.

Supported by Trial 1

Antioxidant activity

Iodide acts as an electron donor in cellular antioxidant reactions and may help neutralize hydrogen peroxide produced during thyroid hormone synthesis, protecting thyroid tissue.

Supported by Trial 1

Mechanism of action

1

Thyroid hormone synthesis

Iodide is actively transported into thyroid follicular cells by the sodium-iodide symporter, oxidized by thyroid peroxidase (TPO), and incorporated into tyrosine residues on thyroglobulin to form T3 and T4.

2

HPT axis regulation

Thyroid hormone levels are tightly controlled by the hypothalamic-pituitary-thyroid (HPT) axis. Low T3/T4 triggers TSH release, stimulating thyroid iodine uptake and hormone synthesis. Iodine deficiency leads to compensatory goiter formation.

Clinical trials

1
Iodine Supplementation and Cognition in Mildly Deficient Children — RCT
PubMed

Randomized controlled trial of iodine supplementation (150 µg/day) vs placebo in 184 mildly iodine-deficient children aged 10-13 in New Zealand for 28 weeks. Outcomes: cognitive function (perceptual reasoning, processing speed, working memory), thyroid function. (Gordon et al. 2009, Am J Clin Nutr)

184 mildly iodine-deficient children. 28-week intervention.

Iodine supplementation significantly improved perceptual reasoning and overall cognitive performance vs placebo. Underscores cognitive importance of adequate iodine status — even mild deficiency affects cognition. Population-level public health implication: maintaining iodized salt programs is critical.

Side effects and drug interactions

Common Potential side effects

Thyroid dysfunction (both hypo- and hyperthyroidism) with chronic excess intake
Acne-like skin eruptions (iodism) at very high doses
Metallic taste and GI irritation with high-dose iodide supplementation

Important Drug interactions

Antithyroid drugs (methimazole, propylthiouracil) — iodine may interfere with treatment
Lithium — combined use increases hypothyroid risk
ACE inhibitors and potassium-sparing diuretics — potassium iodide may raise potassium levels

Featured in these supplement guides

Thyroid Support→

More Thyroid Health Ingredients

Thyroid Health
Potassium Iodide (KI)
Potassium iodide (KI) is the pharmaceutical/inorganic form of iodine — well-characterized,…
Antioxidant
Selenium
Selenium is an essential trace mineral that the body uses to build antioxidant enzymes (su…
Antioxidant
Selenomethionine
Selenomethionine is the organic form of selenium — naturally found in foods (Brazil nuts,…
Antioxidant
SelenoForce® (Selenium-Enriched Yeast — Sabinsa)
SelenoForce® is Sabinsa's branded selenium-enriched Saccharomyces cerevisiae yeast — a foo…

Explore Other Ingredients

Energy
Iron
Iron is an essential mineral best known for its central role in making hemoglobin, the pro…
Cognitive
Phosphatidylserine
Phosphatidylserine (PS) is a phospholipid concentrated in neuronal cell membranes (10-20%…
Athletic Performance
Cordyceps
Cordyceps is a medicinal mushroom traditionally prized as an energy and vitality tonic, po…

Frequently asked questions about Iodine

How much iodine should I take?

The RDA is 150 mcg per day for adults, and 220 to 290 mcg in pregnancy and breastfeeding. Most people in countries using iodized salt get enough. Supplements often provide around 150 mcg; avoid routinely taking very high doses.

What is iodine good for?

Iodine is essential for making thyroid hormones, which regulate metabolism, growth, and development. Adequate iodine is especially important during pregnancy for the baby's brain development.

Can you take too much iodine?

Yes. Both too little and too much iodine can disrupt thyroid function. Very high doses, such as from some kelp supplements, can trigger or worsen thyroid problems in susceptible people. Stay near the recommended amount unless a doctor advises otherwise.

Should I take iodine or kelp for my thyroid?

If you use iodized salt or eat seafood and dairy, you likely get enough already, and extra iodine will not help a thyroid that is not iodine-deficient. Kelp can deliver erratic, very high doses. Check with your doctor before supplementing iodine for thyroid concerns.

What is Iodine?

Iodine is an essential trace mineral that the thyroid gland uses to make thyroid hormones, which regulate metabolism, growth, and development throughout the body. Adequate iodine is especially critical during pregnancy for healthy fetal brain development.

What is Iodine used for?

Iodine is researched primarily for Thyroid Health. Iodine is incorporated into thyroxine (T4) and triiodothyronine (T3) by the thyroid gland. These hormones regulate basal metabolic rate, protein synthesis, and nearly every organ system in the body.

What are the signs of Iodine deficiency?

Iodine deficiency was once endemic in the US Midwest 'goiter belt' but largely eliminated by salt iodization beginning in 1924. It remains one of the world's most common preventable causes of intellectual disability — severe deficiency during pregnancy causes irreversible brain damage and cretinism in offspring.

What is the recommended dosage of Iodine?

The clinically studied dose is 150 mcg/day (adults RDA); 220–290 mcg/day (pregnancy/lactation); upper limit 1,100 mcg/day Always follow the product label and check with a healthcare provider for personal advice.

Is Iodine safe, and does it have side effects?

For most healthy adults, Iodine is well tolerated at studied doses. Reported effects can include: Thyroid dysfunction (both hypo- and hyperthyroidism) with chronic excess intake Acne-like skin eruptions (iodism) at very high doses It may also interact with some medications. Iodine is not right for everyone, so check with a healthcare provider first if you are pregnant or breastfeeding, have a medical condition, or take prescription medication.

Does Iodine interact with any medications?

Possible interactions include: Antithyroid drugs (methimazole, propylthiouracil) — iodine may interfere with treatment Lithium — combined use increases hypothyroid risk If you take prescription medication, check with a pharmacist or doctor before using it.

How strong is the scientific evidence for Iodine?

NutraSmarts rates the evidence for Iodine as Very Strong (5 out of 5). It is backed by 1 clinical trial and 5 cited references summarized on this page. A higher rating reflects more, larger, and better-designed human studies.

References(5 citations)

Evidence ratings on NutraSmarts are based on the totality of human clinical research, with emphasis on randomized controlled trials, meta-analyses, and systematic reviews. The references below directly support claims made throughout this page.

  1. Zimmermann MB, Jooste PL, Pandav CS. Iodine-deficiency disorders. Lancet. 2008;372(9645):1251-62. doi: 10.1016/S0140-6736(08)61005-3.PubMedUsed to support: Authoritative Lancet seminar on iodine-deficiency disorders: goiter, hypothyroidism, cretinism, and impaired neurodevelopment; iodine deficiency is the leading preventable cause of intellectual impairment worldwide; salt iodization is the primary control strategy.
  2. Zimmermann MB. Iodine deficiency. Endocr Rev. 2009;30(4):376-408. doi: 10.1210/er.2009-0011.PubMedUsed to support: Comprehensive review of iodine physiology, thyroid hormone synthesis, assessment of iodine status, and the spectrum of iodine-deficiency disorders across the life cycle.
  3. Bath SC, Steer CD, Golding J, Emmett P, Rayman MP. Effect of inadequate iodine status in UK pregnant women on cognitive outcomes in their children: results from the Avon Longitudinal Study of Parents and Children (ALSPAC). Lancet. 2013;382(9889):331-7. doi: 10.1016/S0140-6736(13)60436-5.PubMedUsed to support: Large prospective cohort (ALSPAC). Children of mothers who were iodine-deficient in early pregnancy had significantly lower verbal IQ and reading scores at age 8-9. Links maternal iodine status to offspring neurodevelopment even in a mildly deficient population.
  4. Zhou SJ, Anderson AJ, Gibson RA, Makrides M. Effect of iodine supplementation in pregnancy on child development and other clinical outcomes: a systematic review of randomized controlled trials. Am J Clin Nutr. 2013;98(5):1241-54. doi: 10.3945/ajcn.113.065854.PubMedUsed to support: Systematic review of RCTs of maternal iodine supplementation. Found limited high-quality trial evidence and no clear proof of improved child cognition from supplementation in mildly-to-moderately deficient areas — an honest counterweight to the observational data.
  5. 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;112(2):389-412. doi: 10.1093/ajcn/nqaa071.PubMedUsed to support: Systematic review/meta-analysis. Iodine supplementation in pregnancy improved some maternal thyroid measures but evidence for improved child neurodevelopment was insufficient/inconclusive in mild-to-moderate deficiency.