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Iodine

Evidence Fact Sheet

Iodine is an essential trace mineral and the rate-limiting substrate for thyroid hormone (T3/T4) synthesis. EFSA authorizes function claims for thyroid, cognition, nervous system, energy metabolism and skin. Research findings are mixed: pediatric RCTs show cognitive benefit in deficient children, while landmark maternal-supplementation trials found no child IQ effect.

Also known as: Iodo · Iode · Yodo · Iodide · Potassium iodide · Potassium iodate · I

Overview

Iodine is an essential trace mineral that serves as the rate-limiting substrate for thyroid hormone biosynthesis (T3 and T4) via thyroid-peroxidase-catalysed iodination of tyrosine on thyroglobulin; thyroid hormones in turn regulate basal metabolic rate and, during fetal/neonatal life, neuronal myelination and brain development. It is typically supplied as potassium iodide or potassium iodate, with adult reference intakes around 150 mcg/day and tolerable upper limits set by EFSA (600 mcg/day) and IOM (1100 mcg/day). Regulatory status: EFSA Reg 432/2012 authorizes five function claims (thyroid, cognition, nervous system, energy metabolism, skin); in the US it is a GRAS essential nutrient marketed under DSHEA structure/function claims with no SSA health claim; ANVISA and China (GB 14880) recognize it as a permitted fortification nutrient. Excess chronic intake can precipitate thyroid dysfunction, so doses are kept within recommended ranges.

Mechanism of Action

Essential substrate for thyroid hormone biosynthesis (T3/T4) via iodination of tyrosine residues on thyroglobulin · Supports thyroid peroxidase (TPO) catalysed organification of iodide in the thyroid follicular lumen · Thyroid hormones regulate basal metabolic rate and mitochondrial energy-yielding metabolism in peripheral tissues · T3/T4 mediated regulation of neuronal myelination and synaptogenesis during fetal and early postnatal brain development · Trace antimicrobial / antioxidant activity in extra-thyroidal tissues (mammary gland, gastric mucosa, salivary glands)

Body systems: Endocrine & Metabolic · Neurological & Cognitive · Skin & Connective Tissue · METABOLISM

Evidence-Based Benefits

Each benefit below is anchored to a specific PubMed-indexed study. Effect sizes, sample sizes, and p-values are reported as published; no values are inferred. Honest negatives and null results are kept alongside the positive findings, and disease-research populations are described as such — Iodine is not characterized as a treatment for any disease.

Maternal Supplementation and Child Neurodevelopment

Null / no benefit RCT supported
  • -0.7verbal IQ diff · p=0.77
  • -1.6performance IQ diff · p=0.44
  • 313 childrenanalysed at age 5-6

In this landmark double-blind RCT, mildly iodine-deficient pregnant women in India and Thailand received 200 mcg iodine daily or placebo. At age 5-6 years their children showed no benefit in verbal or performance IQ. An honest negative for routine maternal supplementation in mild deficiency.

Reported effect: Verbal IQ mean difference -0.7 (95% CI -2.9 to 1.5; p=0.77); performance IQ mean difference -1.6 (95% CI -4.5 to 1.3; p=0.44); 313 children analysed (iodine n=159, placebo n=154)

“Mean difference -0.7 (95% CI -2.9 to 1.5; p=0.77) ... Performance IQ: Mean difference -1.6 (95% CI -4.5 to 1.3; p=0.44) ... Daily iodine supplementation in mildly iodine-deficient pregnant women had no effect on child neurodevelopment at age 5-6 years.”

Source: PMID 29030199 · Gowachirapant 2017 · Lancet Diabetes Endocrinol

Maternal Thyroid Function and Infant Neurodevelopment (Pooled)

Null / no benefit Meta-analysis supported
  • 37 publications10 RCTs · 23 observational
  • -0.18child cognitive MD
  • 1.28language MD (ns)

This systematic review and meta-analysis pooled trials of iodine supplementation in mildly-to-moderately deficient pregnant women. It found no effect on child cognitive, language or motor scores and judged the evidence insufficient to support current pregnancy supplementation recommendations in mild-to-moderate deficiency.

Reported effect: No effect on child cognitive (MD -0.18; 95% CI -1.22, 0.87), language (MD 1.28; 95% CI -0.28, 2.83), or motor scores (MD 0.28; 95% CI -1.10, 1.66); 37 publications included (10 RCTs, 4 non-RCT, 23 observational)

“no effect on child cognitive [mean difference (MD): -0.18; 95% CI: -1.22, 0.87], language (MD: 1.28; 95% CI: -0.28, 2.83), or motor scores (MD: 0.28; 95% CI: -1.10, 1.66) ... There is insufficient good-quality evidence to support current recommendations for iodine supplementation in pregnancy in areas of mild-to-moderate deficiency.”

Source: PMID 32320029 · Dineva 2020 · Am J Clin Nutr

Cognition in Mildly Iodine-Deficient Schoolchildren

RCT supported
  • 0.19 SDsoverall cognitive score · P=0.011
  • 184 childrenaged 10-13 y
  • 150 microgdaily dose · 28 wk

In a double-blind RCT of mildly iodine-deficient New Zealand children, 150 mcg iodine daily for 28 weeks raised the overall cognitive score by 0.19 SD versus placebo, improving perceptual-reasoning subtests (picture concepts and matrix reasoning). A positive finding distinct from the null maternal trials.

Reported effect: Overall cognitive score 0.19 SDs higher than placebo (P=0.011); significant on 2 of 4 subtests: picture concepts (P=0.023) and matrix reasoning (P=0.040); 184 children aged 10-13 y, 150 microg I/day for 28 wk

“The overall cognitive score of the iodine-supplemented group was 0.19 SDs higher than that of the placebo group (P = 0.011). ... significantly improved scores for 2 of the 4 cognitive subtests [picture concepts (P = 0.023) and matrix reasoning (P = 0.040)]”

Source: PMID 19726593 · Gordon 2009 · Am J Clin Nutr

Cognition in Moderately Iodine-Deficient Schoolchildren

RCT supported
  • 4 of 7 testsimproved · P<0.0001
  • 310 childrenaged 10-12 y
  • 172 microg/Lmedian urinary iodine at 24 wk

In a randomized double-blind trial of 310 moderately iodine-deficient Albanian schoolchildren given iodized oil, iodine repletion significantly improved 4 of 7 cognitive tests including rapid target marking, symbol search, rapid object naming and Raven's matrices, indicating gains in information processing and visual problem solving.

Reported effect: Iodine treatment significantly improved performance on 4 of 7 tests (rapid target marking, symbol search, rapid object naming, Raven's Coloured Progressive Matrices; P < 0.0001); n=310 children aged 10-12 y; at 24 wk median urinary iodine 172 microg/L

“Iodine treatment significantly improved performance on 4 of 7 tests: rapid target marking, symbol search, rapid object naming, and Raven's Coloured Progressive Matrices (P < 0.0001). ... Information processing, fine motor skills, and visual problem solving are improved by iodine repletion in moderately iodine-deficient schoolchildren.”

Source: PMID 16400058 · Zimmermann 2006 · Am J Clin Nutr

Cyclic Mastalgia / Fibrocystic Breast Pain

RCT supported
  • 111 womeneuthyroid · double-blind
  • p < 0.01Lewin pain scale vs placebo
  • More than 50%6.0 mg/day group responders

In a randomized, double-blind, placebo-controlled multicenter trial of 111 euthyroid women with cyclic breast pain, molecular iodine (1.5-6.0 mg/day) produced a dose-related, statistically significant reduction in the Lewin overall pain scale; over half of the 6.0 mg/day group achieved a clinically significant reduction in pain.

Reported effect: Dose-related significant improvement in Lewin overall pain scale for all treated groups vs placebo (p < 0.01); more than 50% of the 6.0 mg/day group recorded a clinically significant reduction in overall pain; n=111 women

“A statistically significant improvement (p < 0.01) associated with dose was observed in the Lewin overall pain scale for all treated groups compared to placebo. ... More than 50% of the 6.0 mg/day treatment group recorded a clinically significant reduction in overall pain.”

Source: PMID 15239792 · Kessler 2004 · Breast J

Dosage (research context · not a recommendation)

Adult RDA 150 mcg/day (EFSA AI 150 mcg/day adults; WHO RNI 150 mcg/day). Pregnancy: 220-250 mcg/day (WHO/IOM). Lactation: 250-290 mcg/day. Upper Limit (UL): EFSA 600 mcg/day adults; IOM 1100 mcg/day adults. Typical supplement doses: 100-225 mcg/day as potassium iodide or potassium iodate. Avoid chronic intake >1100 mcg/day (risk of iodine-induced hyperthyroidism or autoimmune thyroiditis exacerbation).

Regulatory Status · 4 Markets

US · FDA
FDA: No SSA (Significant Scientific Agreement) authorized health claim exists for iodine under 21 CFR Part 101 Subpart E (the 12 SSA-eligible nutrients do not include iodine). Iodine is a recognized essential nutrient with an established RDI (150 mcg) per 21 CFR 101.9. Marketed in dietary supplements under DSHEA (1994) — structure/function claims permitted (e.g. "supports thyroid function", "supports normal energy metabolism") provided they carry the mandatory DSHEA disclaimer ("This statement has not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.") and the manufacturer notifies FDA within 30 days of first marketing per 21 USC 343(r)(6). GRAS status as a nutrient (potassium iodide, cuprous iodide, calcium iodate) for use in iodized salt and infant formula per 21 CFR 184.1634 / 21 CFR 184.1635.
EU · EFSA
EFSA / EU Commission Regulation (EU) 432/2012 authorizes 5 health claims for iodine in the Annex (Article 13.1 function claims), each subject to the condition that the food is at least a source of iodine per Annex to Regulation (EC) 1924/2006 (>=15% of NRV per 100 g / 100 mL / per portion). NRV for iodine = 150 mcg (Regulation 1169/2011 Annex XIII). EFSA Tolerable Upper Intake Level (UL): 600 mcg/day adults; 200 mcg/day children 1-3 y; 250 mcg/day 4-6 y; 300 mcg/day 7-10 y; 450 mcg/day 11-14 y; 500 mcg/day 15-17 y. EFSA NDA Adequate Intake (AI, 2014): 150 mcg/day adults, 200 mcg/day pregnancy and lactation.
CN · China
Established nutrient (SAMR): iodine is a GB 14880 permitted nutritional fortification substance, and potassium iodide / potassium iodate are statutory additives for iodized salt; iodine-related health-food function claims require SAMR health-food registration
BR · ANVISA
ANVISA Instrução Normativa IN 28/2018 Anexo V authorizes iodine ("iodo") functional claims for dietary supplements ("suplementos alimentares") when the product delivers the minimum iodine content per portion specified in Anexo III of the same IN and complies with RDC 243/2018 and RDC 27/2010 labelling rules. Brazilian iodization of table salt mandated by Lei 6.150/1974 and RDC 23/2013 (15-45 mg iodine/kg salt). Pregnancy/lactation supplementation guidance per Ministério da Saúde / SBEM Departamento de Tireoide.

Authorized Claims

ANVISA — “O iodo auxilia no metabolismo energético.” (ANVISA IN 28/2018 Anexo V)

Safety

Generally safe within recommended ranges. Excess intake (>1100 mcg/day adults chronic) may precipitate iodine-induced hyperthyroidism (Jod-Basedow phenomenon), hypothyroidism (Wolff-Chaikoff escape failure), or exacerbate autoimmune thyroid disease (Hashimoto, Graves). Contraindicated or requires medical supervision in patients with pre-existing autoimmune thyroid disease, multinodular goitre, or thyroid carcinoma. Caution in pregnancy if dose >500 mcg/day. Rare hypersensitivity to iodine-containing compounds. Potassium iodide may cause GI irritation, metallic taste, sialadenitis at high doses. Drug interactions: lithium (additive hypothyroid risk), amiodarone (iodine-rich), anti-thyroid drugs (methimazole/PTU).

Goals: longevity-stack · cognitive-support

Lifestyles: senior-60-plus

References

PubMed-indexed citations anchoring the benefit findings above. Effect sizes are reported as published.

  1. PMID 29030199 · Gowachirapant 2017 · Lancet Diabetes Endocrinol — Maternal Supplementation and Child Neurodevelopment
  2. PMID 32320029 · Dineva 2020 · Am J Clin Nutr — Maternal Thyroid Function and Infant Neurodevelopment (Pooled)
  3. PMID 19726593 · Gordon 2009 · Am J Clin Nutr — Cognition in Mildly Iodine-Deficient Schoolchildren
  4. PMID 16400058 · Zimmermann 2006 · Am J Clin Nutr — Cognition in Moderately Iodine-Deficient Schoolchildren
  5. PMID 15239792 · Kessler 2004 · Breast J — Cyclic Mastalgia / Fibrocystic Breast Pain

Frequently Asked Questions

1. Does iodine supplementation in pregnancy improve a child's IQ?

Not in the strongest trials conducted in mild deficiency. The landmark Gowachirapant 2017 double-blind RCT (313 children) found no effect of 200 mcg/day maternal iodine on child verbal IQ (difference -0.7, p=0.77) or performance IQ (difference -1.6, p=0.44) at age 5-6. The Dineva 2020 meta-analysis (37 publications) reached the same conclusion, finding no effect on child cognitive, language or motor scores. This is an honest negative for routine supplementation in mildly-to-moderately deficient pregnant women.

2. Then who shows a cognitive benefit from iodine in studies?

The positive signal comes from supplementing deficient children directly, not their mothers. In Gordon 2009, mildly deficient 10-13-year-olds given 150 mcg/day for 28 weeks scored 0.19 SD higher on overall cognition (P=0.011). In Zimmermann 2006, moderately deficient Albanian schoolchildren improved on 4 of 7 cognitive tests (P<0.0001). The benefit appears tied to correcting an existing deficiency.

3. Has iodine been studied for breast pain?

Yes. The Kessler 2004 randomized, double-blind, placebo-controlled trial in 111 euthyroid women with cyclic mastalgia found molecular iodine produced a dose-related, significant reduction in the Lewin overall pain scale (p<0.01), with more than 50% of the 6.0 mg/day group reporting a clinically significant reduction. This is a research finding in a studied population, not a treatment recommendation.

4. What is iodine's established role and regulatory status?

Iodine is the essential substrate for thyroid hormone (T3/T4) synthesis, which regulates metabolic rate and supports nervous-system and cognitive function. EFSA Regulation 432/2012 authorizes five function claims (thyroid, cognition, nervous system, energy metabolism, skin). In the US it is a GRAS essential nutrient marketed under DSHEA structure/function claims, and ANVISA and China's GB 14880 recognize it as a permitted fortification nutrient. Adult reference intake is around 150 mcg/day, with upper limits of 600 mcg/day (EFSA) and 1100 mcg/day (IOM).

Last evidence review: 2026-06-04

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