Iodine

mineraliodine atom

Best with a mealTake with food

What is it

Iodine is an essential trace mineral the thyroid gland uses to make thyroid hormones, which regulate metabolism, growth, and development. Iodine deficiency is the most common preventable cause of intellectual disability worldwide.

How it works

Iodine is absorbed from food and concentrated in the thyroid gland, where it is incorporated into thyroglobulin to make thyroxine (T4) and triiodothyronine (T3). These hormones travel through the bloodstream to regulate basal metabolic rate, growth, brain development, and energy production in nearly every tissue. Deficiency reduces hormone production. The pituitary responds by increasing TSH, which causes the thyroid to enlarge — a goiter. In pregnancy and early childhood, severe deficiency causes irreversible neurological damage and stunted growth (cretinism in its most severe form). Iodized salt has dramatically reduced deficiency in many countries.

Evidence for 5 uses

AI-assisted evidence assessment — talk to your doctor before relying on any single supplement.

Prevention of iodine deficiency and cretinism

Grade A

Strong evidence

Adequate iodine intake during pregnancy and early childhood prevents the irreversible neurological damage caused by severe deficiency. One of the great public health successes of iodized salt.

Treatment of goiter

Grade A

Strong evidence

Goiter caused by iodine deficiency responds to iodine replacement.

Cognitive development in deficient populations

Grade A

Strong evidence

Even mild iodine deficiency in pregnancy is associated with lower IQ in offspring; supplementation improves outcomes.

Radioactive iodine exposure protection

Grade A

Strong evidence

Potassium iodide given before or shortly after radiation exposure blocks thyroid uptake of radioactive iodine. Standard nuclear emergency intervention.

Fibrocystic breast changes

Grade C

Moderate evidence

Some trials suggest high-dose iodine (3 to 6 mg) reduces breast pain and cysts; mechanism is uncertain and high-dose iodine is not benign.

3 commercial forms

Potassium iodide

well absorbed, used in iodized salt

The form added to iodized salt and used in most supplements. Highly bioavailable.

Kelp / sea vegetables

highly variable iodine content

Natural sources of iodine but content varies enormously between products and species. Some kelp supplements provide thousands of mcg per dose, posing risk of excess.

Iodine plus iodide (Lugol's, Iodoral)

high-dose combination products

Provides both iodine and iodide. Marketed at high doses (12.5 mg and above) without clear evidence of benefit and with real risk of thyroid problems.

Dosage

The RDA is 150 mcg per day for adults. Pregnant women need 220 mcg and breastfeeding women 290 mcg. Most multivitamins provide around 150 mcg. The tolerable upper limit is 1,100 mcg per day for adults — exceeding this can cause thyroid dysfunction in susceptible people.

When and how to take it

Iodine absorbs well with or without food. Take consistently at the same time each day. If you take thyroid medication, separate iodine supplements from levothyroxine by several hours since iodine can affect absorption and thyroid function.

Food sources

Food	Amount	%DV
Seaweed (kelp), 1 g dried	16 to 2,984 mcg (highly variable)	—
Cod, 3 oz cooked	158 mcg	105%
Greek yogurt (plain), 1 cup	116 mcg	77%
Iodized salt, 1/4 tsp	76 mcg	51%
Milk (reduced fat), 1 cup	85 mcg	57%
Egg, 1 large	26 mcg	17%
Tuna (canned in oil), 3 oz	17 mcg	11%
Cottage cheese, 1 cup	65 mcg	43%

Safety

At recommended doses iodine is safe. Excess iodine can cause both hypothyroidism (by inhibiting thyroid hormone synthesis — the Wolff-Chaikoff effect) and hyperthyroidism in susceptible individuals (the Jod-Basedow phenomenon). People with autoimmune thyroid disease are particularly sensitive. High-dose iodine supplements (like kelp products providing thousands of mcg) have caused thyroid problems and should be used cautiously. Topical iodine and contrast dyes deliver large amounts and can affect thyroid function temporarily.

Who should be cautious

People with autoimmune thyroid disease (Hashimoto's, Graves') should be cautious with iodine supplements and discuss with their doctor. Pregnant women need adequate iodine but should not exceed the RDA dramatically. People with goiter or thyroid nodules should consult their endocrinologist before iodine supplementation. Healthy people meeting needs through iodized salt usually do not need supplements.

Interactions

Iodine interacts with thyroid medications — both can affect thyroid function and must be balanced. Lithium has anti-thyroid effects that combine with iodine. Amiodarone contains substantial iodine and can cause thyroid dysfunction. ACE inhibitors and potassium-sparing diuretics may raise potassium when used with potassium iodide.

Frequently asked questions

Do I need an iodine supplement?⌄

Most people in countries with iodized salt do not. Pregnant and breastfeeding women, vegans, and people avoiding salt may need supplementation.

Is high-dose iodine (Lugol's, Iodoral) safe?⌄

Not necessarily. Doses of 12.5 mg and above are far above what the body needs and can cause thyroid dysfunction, especially in people with autoimmune thyroid disease.

Can iodine cause hypothyroidism?⌄

Yes, paradoxically — both deficiency and excess can cause hypothyroidism. People with autoimmune thyroid disease are most susceptible.

Should I take iodine if I have Hashimoto's?⌄

Talk to your endocrinologist first. Iodine can sometimes worsen Hashimoto's thyroiditis.

How much iodine is in iodized salt?⌄

About 76 mcg per quarter teaspoon (1.5 g). A typical American diet using iodized salt easily covers the RDA.

References

NIH ODS Iodine Fact Sheet — NIH Office of Dietary Supplements link

Track Iodine with Pilora

Set up dose reminders, check interactions, and join the community in the Pilora iPhone app.

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Disclaimer: These statements have not been evaluated by the FDA. This page is educational, not a substitute for personalized medical advice. Evidence grades are AI-assisted assessments — talk to your doctor before starting any new supplement, especially if you're pregnant, breastfeeding, on medications, or managing a chronic condition.