Iodine
Trace mineralsYour intake
What each level of iodine does
Approximate dose-response bands. Individual response varies — these are starting points, not prescriptions.
- Severely lowYOU ARE HERE0 mcg – 49.5 mcg
Well below target. Risk of deficiency symptoms tied to thyroid hormones.
- Insufficient49.5 mcg – 150 mcg
Below the recommended daily target. Long-term adequacy not assured.
- Adequate150 mcg – 225 mcg
Daily target met. Standard nutritional support for thyroid hormones.
- Therapeutic225 mcg – 300 mcg
Common for specific health goals. Check the evidence for your situation before sustaining this level.
- High300 mcg – 1100 mcg
Approaching the tolerable upper limit. Monitor and consider clinical guidance.
- Over upper limit1100 mcg – +
Above the tolerable upper limit. Risk of adverse effects — back off or consult a clinician.
Overview
Trace mineral required for thyroid hormone synthesis (T3, T4) and only thyroid hormone synthesis. Universal salt iodisation programs have eliminated cretinism and goitre across most of the world, but deficiency remains a public health issue and excess from kelp supplements can trigger thyroid dysfunction.
Functions
- ●Component of T4 (4 iodine atoms) and T3 (3 iodine atoms)
- ●Required for fetal/infant brain development
- ●Modulates BMR via thyroid hormone action
- ●Possible role in breast tissue iodine pooling (controversial)
Mechanism
Iodide is actively transported into the thyroid follicular cell via the Na/I symporter (NIS), oxidised by thyroid peroxidase, and incorporated into tyrosine residues on thyroglobulin to form MIT and DIT. Coupling produces T4 and T3, stored in colloid, and released into circulation under TSH stimulation. Severe iodine deficiency in pregnancy causes irreversible neurological damage in offspring.
Benefits
- ●Prevents goitre and cretinism
- ●Supports normal thyroid function and metabolism
- ●Required for normal fetal/infant neurodevelopment
- ●Treatment for radioactive iodine exposure (KI flooding the thyroid)
Deficiency
Mild-to-moderate deficiency affects ~2 billion people globally despite iodisation programs. Pregnant women in regions without iodised salt or seafood are highest risk.
- ●Goitre (compensatory thyroid enlargement)
- ●Hypothyroidism — fatigue, cold intolerance, weight gain
- ●Cretinism (infant — irreversible neurological deficit)
- ●Reduced fertility
- ●Cognitive impairment in iodine-deficient pregnancies
- ●Pregnant and lactating women
- ●Vegans (no seafood, limited dairy)
- ●Regions without iodised salt programs
- ●Use of non-iodised speciality salts (Himalayan, kosher) without other iodine source
Excess
Excess can trigger hypothyroidism (Wolff-Chaikoff effect) or hyperthyroidism (Jod-Basedow), particularly in adults with subclinical thyroid nodules. Kelp supplements are the typical culprit — content varies 100× batch-to-batch.
- ●Hyperthyroidism (Jod-Basedow) — palpitations, weight loss, tremor
- ●Hypothyroidism (paradoxical) in susceptible individuals
- ●Thyroiditis (acute)
- ●Brassy/metallic taste
- ●Acneiform eruption
Forms
- Potassium iodide (KI)Standard supplement form; reliable, consistent dose
- Iodised salt (KIO3 or KI)Public health workhorse; ~45 mcg per 1/4 tsp
- Kelp / seaweedVariable iodine content; can deliver toxic doses; avoid as primary supplement
- Lugol's solution / SSKIPharmacologic; for thyroid emergencies and radiation exposure only
- Povidone-iodineTopical antiseptic; small systemic absorption
Food sources
- Kelp (dried) · 1 g15–3,000 mcg (highly variable)
- Cod (cooked) · 3 oz100 mcg
- Iodized salt · 1/4 tsp75 mcg
- Milk · 1 cup85 mcg
- Egg (whole) · 1 large25 mcg
- Plain yogurt · 1 cup75 mcg
Supplement forms
Potassium iodide (from a multivitamin or prenatal at 150 mcg) is reliable. Kelp-based supplements vary 100× in iodine content batch-to-batch and can deliver doses far above the UL. Pregnant and breastfeeding women should specifically check that their prenatal contains iodine — many do not.
Bioavailability
Iodide is ~95% absorbed. Iodine bound to algae (kelp) or amino acids requires more digestion but is also well-absorbed. The thyroid concentrates iodide ~30–40× plasma levels via the Na/I symporter.
Longevity relevance
Adequacy throughout life supports normal metabolic rate, cognition, and fertility. Pregnancy iodine deficiency has the largest population-level legacy effect — IQ reductions persist for the child's lifetime. Excess from kelp / unregulated supplements is the modern over-correction.
Relationships
- Selenium · Required for thyroid peroxidase and deiodinases — iodine alone can't power thyroid if selenium is low
- Iron, zinc, vitamin A · All co-required for normal thyroid hormone synthesis and metabolism
- Goitrogens (raw cruciferous, soy, cassava, millet) · Mild thyroid uptake inhibition; only relevant at high intake with low iodine
- Perchlorate, thiocyanate, nitrate · Competitively inhibit NIS uptake; environmental concern
- Lithium · Inhibits iodide release from thyroid
References
- NIH ODS — Iodineguideline
- Linus Pauling Institute — Iodinereview
- WHO — iodine deficiency status (2007)guideline
About Iodine
Thyroid hormone (T3/T4) synthesis.
- Role
- Thyroid hormones
- Daily target
- 150 mcg (DV)
- Upper limit
- 1100 mcg
- Also called
- iodine, potassium iodide, kelp
The mechanisms and systems this nutrient feeds. Click any to drill into what runs on it.
★ = load-bearing / primary cofactor. Track these in My Journey.
Top food sources of Iodine
Whole foods that contribute meaningfully (≥10% DV per 100 g serving). Click any food to see its full nutrient profile and what else it brings to the table.