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Moderate evidenceGeneral health

Iodine

Iodine is genuinely essential and correcting severe deficiency prevents goitre and cretinism. But in mildly deficient populations the largest randomised trial found no benefit at all to children's IQ, and over-supplementing can cause the very thyroid disease you were trying to prevent.

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What the science says

  • No IQ benefit from supplementing mildly-to-moderately deficient pregnancies Limited evidence

    A double-blind RCT gave 200 mcg/day iodine or placebo from before 14 weeks' gestation to women in mildly iodine-deficient areas of India and Thailand. At age 5-6, children's verbal IQ was 89.5 versus 90.2 (difference -0.7, 95% CI -2.9 to 1.5) and performance IQ 97.5 versus 99.1 (difference -1.6, 95% CI -4.5 to 1.3) — no benefit. Severe deficiency is a completely different situation, but the mild-deficiency case is not supported.

  • Improves maternal thyroid markers; child outcome data are insufficient Moderate evidence

    A Cochrane review of 14 studies found iodine in pregnancy reduced postpartum goitre (RR 0.32, 95% CI 0.11-0.91) but showed no clear effect on maternal hypothyroidism, preterm birth, low birthweight or neonatal thyroid function — while increasing digestive intolerance roughly 15-fold. The authors concluded there were insufficient data to reach meaningful conclusions on most outcomes of interest.

  • Reduces thyroid volume in mild deficiency, with a weak cognitive signal in children Limited evidence

    A systematic review of 9 RCTs and 8 observational studies found supplementation in mild-to-moderate deficiency reduced maternal thyroid volume and serum thyroglobulin. A pooled analysis of two trials in school-age children showed modest gains in perceptual reasoning (SMD 0.55, 95% CI 0.05-1.04) and global cognitive index (SMD 0.27, 95% CI 0.10-0.44), with significant heterogeneity between the two studies.

Dosage & safety

Studied doseRDA is 150 mcg/day for adults, 220 mcg/day in pregnancy and 290 mcg/day while breastfeeding. Prenatal supplements typically provide 150 mcg as potassium iodide. Iodised salt, dairy, eggs and seafood cover most people in fortified countries — check whether your salt is iodised before assuming a gap. The tolerable upper limit is 1,100 mcg/day for adults.
SafetyBoth too little and too much iodine cause thyroid disease, and the dose-response is U-shaped. Acute excess can trigger the Wolff-Chaikoff effect (hypothyroidism) or, in people with autonomous thyroid nodules, Jod-Basedow hyperthyroidism; chronic excess raises rates of autoimmune thyroiditis. Kelp and seaweed supplements are the main real-world hazard — some deliver several thousand micrograms per capsule with inconsistent labelling, and they may also carry inorganic arsenic. Avoid high-dose iodine in Hashimoto's thyroiditis, Graves' disease and nodular goitre without endocrinology input. Interacts with lithium, amiodarone (itself iodine-rich), and antithyroid drugs. Potassium iodide at 130 mg is a radiation-emergency medication, not a nutritional supplement.

How to take it

TimingTiming does not matter.
With food?With or without food.
Worth knowingCheck whether your salt is iodised and whether your prenatal already contains 150 mcg before adding anything — the dose-response for iodine is U-shaped and too much causes the same diseases as too little.

Interactions

With medications

  • lithium

    Both lithium and iodine excess suppress thyroid function; together the risk of hypothyroidism and goitre is higher. do not add iodine supplements on lithium without thyroid monitoring

  • amiodarone

    Amiodarone is itself extremely iodine-rich and already causes thyroid dysfunction — added iodine compounds the problem. avoid iodine supplements while on amiodarone

  • antithyroid drugs (methimazole, propylthiouracil, carbimazole)

    Iodine directly opposes the treatment and can destabilise control of hyperthyroidism. do not supplement without your endocrinologist

  • ACE inhibitors, ARBs and potassium-sparing diuretics

    If the product is potassium iodide, the potassium load adds to drugs that already raise potassium. relevant mainly at high-dose potassium iodide; check the label if you take these

With other supplements

  • kelp and seaweed products

    Kelp can deliver several thousand micrograms of unlabelled iodine per capsule, stacking silently on top of any iodine supplement or prenatal. do not combine; pick one standardised source

Well-established interactions only — this is not a complete list. Always tell your doctor and pharmacist what you take.

Frequently asked questions

Should I take iodine during pregnancy?

In mildly deficient areas, a large trial of 200 mcg/day of iodine found no benefit to children's IQ at age 5–6, so that evidence is limited. The iodine RDA in pregnancy is 220 mcg/day; check whether your salt is iodised and your prenatal already contains 150 mcg before adding more.

Can too much iodine harm your thyroid?

Yes. The iodine dose-response is U-shaped: too much iodine can cause hypothyroidism, hyperthyroidism in people with nodules, and more autoimmune thyroiditis. The adult upper limit is 1,100 mcg/day.

Are kelp supplements a safe source of iodine?

Kelp is the main real-world iodine hazard: some products deliver several thousand micrograms per capsule with inconsistent labels and may carry inorganic arsenic. Pick one standardised iodine source instead.

Is iodine safe with Hashimoto's or Graves' disease?

Avoid high-dose iodine in Hashimoto's, Graves' disease and nodular goitre without endocrinology input. Iodine also interacts with lithium, amiodarone and antithyroid drugs.

Scientific references

Where to buy

Nutri, Potassium Iodide Tablets, 140 Tablets (65 mg per Tablet)

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