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Trace mineral

Iodine

Thyroid hormone (T3/T4) synthesis; metabolism, fetal brain development

Essential nutrient

Reference intakes (RDA or AI) are set by the National Academies of Sciences, Engineering, and Medicine. Deficiency thresholds come from clinical and WHO guidance.

At a glance

Women, 19-50

150 mcg (220 mcg pregnancy, 290 mcg lactation)

Men, 19-50

150 mcg

Upper limit (adults)

1,100 mcg/day

How common is deficiency?

COMMON worldwide (about 2 billion people at risk); mild deficiency found in some US women of reproductive age

Food sources

Animal sources

Cod, seaweed-fed fish, shrimp, dairy, eggs, tuna

Plant sources

Seaweed (kelp, nori - variable amounts), iodized salt; plant content depends on soil iodine

Deficiency and testing

Signs of deficiency

Goiter (enlarged thyroid), fatigue, weight gain, cold intolerance, dry skin, hair loss, constipation, hypothyroidism; cretinism and cognitive impairment in offspring

Who is at higher risk

Pregnant and breastfeeding women, people avoiding iodized salt/dairy/seafood (vegans), residents of iodine-poor regions, high goitrogen intake

How it is tested

Urinary iodine concentration (spot or 24 h); TSH; free T4; thyroglobulin; thyroid ultrasound

Cut-offs

Population median urinary iodine <100 mcg/L = insufficient (WHO); <20 mcg/L = severe. Individual spot values vary a lot

Symptoms are not specific. Only a clinician with the right tests can tell whether you are deficient.

Supplement forms

Common forms

potassium iodide, potassium iodate, sodium iodide, iodized salt, kelp/seaweed tablets.

More effective

iodized salt and prenatal vitamins with potassium iodide or iodate at 150 mcg (reliable dose, almost completely absorbed).

Less effective

kelp and seaweed supplements (iodine content varies widely, from very low to above the UL, which can trigger thyroid dysfunction); taking iodine without testing in people with autoimmune thyroid disease; sea salt (usually not iodized).

Safety, interactions and halal notes

Safety and interactions

Upper limit for adults: 1,100 mcg/day. Going above the upper limit over time can cause harm, so check labels and talk to a clinician before high-dose supplements.

Halal note

The nutrient itself is not a halal question. For supplements, check the delivery form: gelatin (pork or non-halal bovine), capsule shells, glycerin, and alcohol-based carriers need halal certification. Ask for the halal certificate, not just a label claim. This is general guidance, not a certification.

Frequently asked questions

How much Iodine do adults need per day?

Women 19-50: 150 mcg (220 mcg pregnancy, 290 mcg lactation). Men 19-50: 150 mcg. Upper limit: 1,100 mcg/day. Needs change with age, pregnancy and health conditions.

What are the signs of Iodine deficiency?

Goiter (enlarged thyroid), fatigue, weight gain, cold intolerance, dry skin, hair loss, constipation, hypothyroidism; cretinism and cognitive impairment in offspring. These signs are not specific, so only a clinician with the right tests can confirm a deficiency.

What are the best food sources of Iodine?

Animal sources: Cod, seaweed-fed fish, shrimp, dairy, eggs, tuna. Plant sources: Seaweed (kelp, nori - variable amounts), iodized salt; plant content depends on soil iodine.

Which form of Iodine supplement is best?

iodized salt and prenatal vitamins with potassium iodide or iodate at 150 mcg (reliable dose, almost completely absorbed).

Sources

← Back to the full nutrient guide

This page is for education only and is not medical advice. These statements have not been evaluated by the Food and Drug Administration. Supplements are not intended to diagnose, treat, cure or prevent any disease. Talk to a qualified clinician before starting a supplement, especially if you are pregnant, breastfeeding, take medicine or have a medical condition. Daily needs are US reference intakes for adults 19-50.

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