Mineral

Iodine

Iodine (I, element 53)

Evidence TierAWADA NOT PROHIBITED

tuneTypical Dose

150-300 mcg per day

watchEffect Window

Weeks for biochemical normalization of thyroid markers in deficiency correction.

check_circleCompliance

WADA NOT PROHIBITED

Overview

Clinical Summary

Iodine is required for thyroid hormone synthesis and normal growth and neurodevelopment. It is used to correct low iodine intake, particularly in pregnancy and in low seafood or iodized salt diets.

Correcting iodine deficiency prevents goiter and hypothyroid symptoms and supports fetal and infant neurodevelopment. Benefits are clearest in populations with low baseline intake. Minority evidence suggests improvement in fibrocystic breast discomfort in some individuals. Excess iodine can precipitate thyroid dysfunction, especially in autoimmune thyroid disease, so benefit depends on restoring adequacy rather than high dosing.

Essential substrate for thyroid peroxidase-mediated synthesis of T4 and T3. Iodide is actively transported into thyroid follicular cells via the sodium-iodide symporter, organified, and coupled to form thyroid hormones.

Outcomes

What This Is Expected To Influence

Primary Outcomes

  • Prevents goiter and cretinism in iodine-deficient populations
  • Normalizes thyroid hormone levels (T3, T4, TSH) in deficiency

Secondary Outcomes

  • Supports cognitive development in iodine-deficient children
  • Maintains adequate urinary iodine concentration

Safety

Contraindications and Interactions

Contraindications

  • Hashimoto's thyroiditis (may worsen)
  • Graves' disease
  • Uncontrolled thyroid disease

Side effects

  • Metallic taste
  • GI upset (nausea, stomach pain)
  • Acne-like skin lesions at high doses

Interactions

  • Amiodarone (additive thyroid suppression)
  • Lithium (additive thyroid suppression)
  • Anti-thyroid medications (antagonism)

Avoid if

  • Autoimmune thyroid disease without medical supervision
  • Iodine hypersensitivity

Evidence

Study-level References

iodine-SRC-001Narrative review
Sourceopen_in_new

Zimmermann MB. Iodine deficiency. Endocr Rev. 2009;30(4):376-408. PMID:19460960.

Population: General populations, with emphasis on iodine-deficient regions, pregnancy, infancy, and neurodevelopment.

Dose protocol: Population iodine prophylaxis/supplementation strategies. Adequacy framed around physiological intake targets.

Key findings: Iodine deficiency is a leading preventable cause of thyroid dysfunction and impaired neurodevelopment worldwide. Adequate iodine intake prevents endemic goiter and iodine-deficiency hypothyroidism. Maternal iodine deficiency is linked to adverse fetal brain outcomes. Prevention is a core public-health priority. Excess iodine exposure can induce thyroid dysfunction in susceptible individuals, supporting dose-range discipline.

Notes: Workbook context flags non-iodized salt adoption as a practical driver of deficiency re-emergence in some cohorts.

Paper content

This review remains a strong background source for why iodine adequacy matters, especially for thyroid hormone production and fetal neurodevelopment. It is best used as physiology and public-health context rather than as direct trial evidence for supplement benefit in already sufficient adults.

iodine-SRC-002Randomized double-blind placebo-controlled trial
Sourceopen_in_new

Ma ZF, Venn BJ, Manning PJ, Cameron CM, Skeaff SA. Iodine Supplementation of Mildly Iodine-Deficient Adults Lowers Thyroglobulin: A Randomized Controlled Trial. J Clin Endocrinol Metab. 2016;101(4):1737-1744. doi:10.1210/jc.2015-3591. PMID:26891118.

Population: Mildly iodine-deficient adults aged 18 to 40 years in New Zealand.

Dose protocol: 150 mcg/day iodine for 24 weeks in mildly deficient adults

Key findings: Iodine lowered thyroglobulin in mildly deficient adults without major between-group change in TSH or free T4.

Notes: Supports targeted deficiency correction rather than strong thyroid-performance claims.

Paper content

In mildly iodine-deficient adults, standard-dose iodine improved a deficiency biomarker (thyroglobulin) without clearly shifting routine thyroid hormone markers. This supports iodine as deficiency correction rather than a thyroid-performance booster.

iodine-SRC-003Systematic review and meta-analysis
Sourceopen_in_new

Aarsland TE, Aakre I, Stea TH, Henjum S, Markhus MW, Strand TA. Association of Mild-to-Moderate Iodine Deficiency With Thyroid Function-A Systematic Review and Meta-analysis. Adv Nutr. 2025;16(9):100471. PMID:40633808.

Population: General-population observational studies spanning infants, children, adolescents, adults, pregnant women, and lactating women.

Dose protocol: Systematic review and meta-analysis of mild-to-moderate iodine deficiency and thyroid function

Key findings: Mild-to-moderate iodine deficiency has more variable thyroid-function consequences than severe deficiency.

Notes: Useful for calibrating adult expectations and avoiding overstatement.

Paper content

This review is useful for calibrating expectations. Mild-to-moderate iodine deficiency does not always translate into a large or consistent thyroid-function abnormality, which helps explain why adult supplementation trials often improve deficiency markers more clearly than hormone panels.

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