Evidence-based·Last reviewed May 30, 2026·How we grade evidence

Iodine

MineralIodine atomBest with a meal

Useful mainly for people with confirmed or high-risk iodine deficiency; pregnant and breastfeeding women.

Quick decision guide

May help most

People with confirmed or high-risk iodine deficiency; pregnant and breastfeeding women

Common dosing range

150 mcg/day (RDA for adults); 220 mcg/day in pregnancy; 290 mcg/day while breastfeeding

When to expect effects

Weeks for thyroid function normalization; months for developmental outcomes

Watch out for

Excess iodine causes thyroid dysfunction; people with autoimmune thyroid disease are particularly sensitive

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.

Is it worth it for you?

Use this as a quick fit check, not a diagnosis.

Worth considering if…

You have documented iodine deficiency or low dietary iodine (avoid iodized salt, eat little seafood)

You are pregnant or breastfeeding and your prenatal vitamin lacks iodine

You live in an iodine-deficient region

Probably skip if…

You already consume iodized salt and seafood regularly and have no deficiency

You have Hashimoto's thyroiditis or Graves' disease without endocrinologist guidance

You are taking high-dose kelp or iodine supplements above 500 mcg/day without medical monitoring

Evidence at a glance

Goal	Effect	Best fit	Time
iodine deficiency correction Strong Evidence	Definitive: prevents goiter, cretinism, and intellectual disability when given to deficient populations	Populations without reliable iodized salt access; pregnant women in deficient regions	Weeks to months
thyroid hormone production (deficiency-mediated goiter) Strong Evidence	Goiter regression with iodine repletion in deficient individuals	People with endemic goiter due to iodine deficiency	Months
radioactive iodine exposure protection Strong Evidence	Saturates thyroid, blocking radioiodine uptake when given promptly	People near nuclear accidents or who require radiation emergency prophylaxis	Hours (must be taken close to exposure time)
fetal and infant cognitive development Good Evidence	IQ preservation and developmental protection when maternal deficiency is corrected	Pregnant women in iodine-deficient regions	Effects determined in utero and early infancy

iodine deficiency correction

Strong Evidence

Effect: Definitive: prevents goiter, cretinism, and intellectual disability when given to deficient populations
Best fit: Populations without reliable iodized salt access; pregnant women in deficient regions
Time: Weeks to months

thyroid hormone production (deficiency-mediated goiter)

Strong Evidence

Effect: Goiter regression with iodine repletion in deficient individuals
Best fit: People with endemic goiter due to iodine deficiency
Time: Months

radioactive iodine exposure protection

Strong Evidence

Effect: Saturates thyroid, blocking radioiodine uptake when given promptly
Best fit: People near nuclear accidents or who require radiation emergency prophylaxis
Time: Hours (must be taken close to exposure time)

fetal and infant cognitive development

Good Evidence

Effect: IQ preservation and developmental protection when maternal deficiency is corrected
Best fit: Pregnant women in iodine-deficient regions
Time: Effects determined in utero and early infancy

Evidence for 4 uses

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

iodine deficiency correction

Corrects deficiency

Strong Evidence

Iodine is an essential mineral with no metabolic substitute. Deficiency is the world's most common preventable cause of intellectual disability. Iodized salt and supplementation programs have dramatically reduced cretinism and goiter globally. RDA-level supplementation fully corrects deficiency in at-risk individuals.

Effect size

Definitive: prevents goiter, cretinism, and intellectual disability when given to deficient populations

Time to effect

Weeks to months

Best fit

Populations without reliable iodized salt access; pregnant women in deficient regions

Less likely

People with sufficient dietary iodine from iodized salt and seafood

Bottom line: The single clearest indication for iodine supplementation: confirmed deficiency or high-risk populations (pregnancy, low-iodized-salt diets).

SourceCandido et al., 2023 — PubMed Dineva et al., 2020 — PubMed

thyroid hormone production (deficiency-mediated goiter)

Corrects deficiency

Strong Evidence

In iodine-deficient individuals, TSH drives thyroid enlargement to maximize iodine capture. Iodine repletion normalizes TSH and allows goiter regression. This is a well-established causal relationship validated over decades of public health intervention. The effect applies specifically to deficiency-driven goiter; autoimmune thyroid enlargement does not respond beneficially.

Effect size

Goiter regression with iodine repletion in deficient individuals

Time to effect

Months

Best fit

People with endemic goiter due to iodine deficiency

Less likely

People with autoimmune goiter (Hashimoto's, Graves') — iodine may worsen disease

Bottom line: Definitive treatment for iodine-deficiency goiter; does not apply to autoimmune thyroid disease.

SourceLiesenkötter et al., 1996 — PubMed Glinoer et al., 1995 — PubMed

radioactive iodine exposure protection

Disease adjunct

Strong Evidence

High-dose potassium iodide (65–130 mg) is stockpiled by governments as emergency radiation prophylaxis. By saturating thyroid iodide transport, it blocks uptake of radioactive iodine-131 released in nuclear events, reducing thyroid cancer risk. Effectiveness is highly time-dependent — most beneficial within 1–2 hours of exposure. This is a medical emergency indication, not a supplement strategy.

Effect size

Saturates thyroid, blocking radioiodine uptake when given promptly

Time to effect

Hours (must be taken close to exposure time)

Best fit

People near nuclear accidents or who require radiation emergency prophylaxis

Less likely

General population without radioactive iodine exposure risk

Bottom line: Effective thyroid protection in nuclear emergencies only when taken at the right time under public health direction.

SourceDreger et al., 2015 — PMC Pfinder et al., 2016 — PubMed

fetal and infant cognitive development

Corrects deficiency

Good Evidence

Adequate maternal iodine is essential for fetal thyroid hormone production, which drives brain development during the first trimester when the fetus cannot produce its own hormones. Maternal deficiency causes irreversible neurological impairment ranging from mild cognitive deficit to cretinism. Correction of deficiency before or early in pregnancy prevents these outcomes.

Effect size

IQ preservation and developmental protection when maternal deficiency is corrected

Time to effect

Effects determined in utero and early infancy

Best fit

Pregnant women in iodine-deficient regions

Less likely

Pregnant women with adequate iodine intake

Bottom line: Essential for fetal brain development; maternal iodine adequacy during pregnancy is non-negotiable.

SourceDineva et al., 2020 — PubMed

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.

How to take it

1. Typical dose

150 mcg/day for adults; 220 mcg/day in pregnancy; 290 mcg/day breastfeeding (match the RDA — do not exceed 1,100 mcg/day UL without medical direction)

2. Timing

With a meal for best tolerance; consistently at the same time daily

3. With food

Take with food; consistent timing more important than meal timing

4. How long to try

Ongoing to maintain sufficiency; reassess with a clinician if using for a specific condition

What to track

Thyroid function labs (TSH, free T4) if supplementing above RDA

Symptoms of excess (palpitations, weight changes, neck swelling)

Energy and cold tolerance as rough markers of thyroid function

3 commercial forms

Compare the main delivery options and what they’re best suited for.

Potassium iodide

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

well absorbed, used in iodized salt

Kelp / sea vegetables

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.

highly variable iodine content

Iodine plus iodide (Lugol's, Iodoral)

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.

high-dose combination products

Safety

Know the common side effects, key cautions, and who should avoid it.

Common side effects

metallic taste at higher dosesGI upsetacne-like skin lesions with excess intake

Serious risks

Hypothyroidism from Wolff-Chaikoff effect at excess doses
SourceNIH Office of Dietary Supplements — Iodine — NIH ODS
Hyperthyroidism (Jod-Basedow) in susceptible individuals with excess intake
SourceNIH Office of Dietary Supplements — Iodine — NIH ODS
Thyroid storm in Graves' disease with high doses
SourceNIH Office of Dietary Supplements — Iodine — NIH ODS

Who should avoid it

People with Hashimoto's thyroiditis without endocrinologist guidance
SourceNIH Office of Dietary Supplements — Iodine — NIH ODS
People with Graves' disease or hyperthyroidism without medical management
SourceNIH Office of Dietary Supplements — Iodine — NIH ODS
People with thyroid nodules (without specialist guidance)
SourceNIH Office of Dietary Supplements — Iodine — NIH ODS

Pregnancy & breastfeeding

Adequate iodine is essential in pregnancy (220 mcg/day); most prenatal vitamins include it, but check the label — do not dramatically exceed the RDA.

SourceNIH Office of Dietary Supplements — Iodine — NIH ODS

Interactions

amiodaroneMajor

Amiodarone contains large amounts of iodine and frequently causes thyroid dysfunction; additional iodine significantly increases risk

SourceNIH Office of Dietary Supplements — Iodine — NIH ODS

levothyroxine and thyroid medicationsModerate

Iodine directly affects thyroid hormone synthesis; separate from thyroid medications and monitor thyroid labs

SourceNIH Office of Dietary Supplements — Iodine — NIH ODS

lithiumModerate

Both have anti-thyroid effects; combination increases hypothyroidism risk

SourceNIH Office of Dietary Supplements — Iodine — NIH ODS

ACE inhibitors and potassium-sparing diureticsMinor

Potassium iodide can raise serum potassium; monitor when combined with drugs that also elevate potassium

SourceNIH Office of Dietary Supplements — Iodine — NIH ODS

Documented interactions

Evidence-graded pair pages with sources, dosing notes, and timing guidance — a complement to the narrative section above.

Warnings (1)

+ methimazole

high

Methimazole blocks new thyroid hormone synthesis but does not prevent the gland from using iodide already inside it. Adding a large iodine load (kelp, iodine drops, iodine-containing contrast, amiodarone) can fuel hormone production, blunt methimazole's effect, and in some people worsen hyperthyroidism or, rarely, precipitate thyroid storm.

Beneficial pairs (1)

+ selenium

synergy

Iodine is the raw material the thyroid uses to build the hormones T4 and T3, but selenium is required to make the deiodinase enzymes that convert inactive T4 into active T3 in peripheral tissues. Selenium also powers glutathione peroxidase, which protects thyroid cells from the oxidative stress generated during iodine handling. The two minerals work as a pair: each is far less useful without the other.

See all 2 Iodine interactions →

Protocols featuring Iodine

Evidence-backed routines where Iodine plays a role.

Thyroid Foundation (Hypo)

thyroid

Hypothyroidism — outside of autoimmune Hashimoto''s — is most commonly due to iodine deficiency in some populations, selenium deficiency, or post-medical causes (radiation, surgery, medication-induced). In iodine-replete countries, autoimmune Hashimoto''s accounts for the majority of cases (see the Hashimoto''s protocol). This protocol is for non-autoimmune hypothyroidism or subclinical hypothyroidism without elevated TPO antibodies — selenium, low-dose iodine (only if deficiency is documented), tyrosine (precursor to thyroid hormones), and B12 for the fatigue often accompanying hypothyroidism. If you have confirmed Hashimoto''s (positive TPO antibodies), use that protocol instead — iodine supplementation is potentially harmful in autoimmune thyroid disease. Treatment of confirmed hypothyroidism is levothyroxine. Supplements do not replace thyroid hormone replacement. They support endogenous function and address common cofactor deficiencies.

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%

Seaweed (kelp), 1 g dried

Amount: 16 to 2,984 mcg (highly variable)
%DV: —

Cod, 3 oz cooked

Amount: 158 mcg
%DV: 105%

Greek yogurt (plain), 1 cup

Amount: 116 mcg
%DV: 77%

Iodized salt, 1/4 tsp

Amount: 76 mcg
%DV: 51%

Milk (reduced fat), 1 cup

Amount: 85 mcg
%DV: 57%

Egg, 1 large

Amount: 26 mcg
%DV: 17%

Tuna (canned in oil), 3 oz

Amount: 17 mcg
%DV: 11%

Cottage cheese, 1 cup

Amount: 65 mcg
%DV: 43%

Choosing a product

What to look for on the label — and what to be skeptical of.

Look for…

Dose listed in mcg (not mg — confirm unit; 1 mg = 1,000 mcg)

Standard forms: potassium iodide, sodium iodide, or iodine as part of a multivitamin

Kelp products: verify mcg per serving — highly variable and often unpredictable

Be skeptical of…

High-dose iodine (e.g. 12.5 mg/day) is safe for everyone — it is not

Iodine detoxifies heavy metals

Iodine boosts thyroid for weight loss or energy in people with normal thyroid function

Nascent iodine or 'detoxified iodine' are meaningfully superior to standard forms

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 by claim

iodine deficiency correction

Candido et al., 2023 — PubMed (2023) link

Dineva et al., 2020 — PubMed (2020) link

thyroid hormone production (deficiency-mediated goiter)

Liesenkötter et al., 1996 — PubMed (1996) link

Glinoer et al., 1995 — PubMed (1995) link

radioactive iodine exposure protection

Dreger et al., 2015 — PMC (2015) link

Pfinder et al., 2016 — PubMed (2016) link

Safety

NIH Office of Dietary Supplements — Iodine — NIH ODS link

Track Iodine with Pilora

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

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Evidence-based·Last reviewed May 30, 2026·Evidence current as of May 30, 2026·How we grade evidence

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.