Supplement analysis backed by scientific evidence · PT

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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.

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.

Scientific references

Where to buy

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

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