Iodine
EVIDENCE: MODERATEAlso sold as: potassium iodide, iodide, kelp iodine, povidone-iodine
Iodine is needed to make thyroid hormones. Correcting deficiency matters, but extra iodine does not establish further benefits when intake is already adequate. Dental antiseptic research uses topical povidone-iodine, a different preparation from swallowed potassium iodide.
Compiled by iSupplementReviews editorial team ·Updated 2026-10-06 · 4 sources
- Type
- Essential trace mineral
- Studied dose
- RDA 150 mcg/day; correction of deficiency, not supra-nutritional dosing
- Best form
- potassium iodide — the standardized, stable form used in iodized salt
- Upper limit
- UL 1,100 mcg/day (adults, US)
- Our rating
- MODERATE — Several human trials — limits in size, duration, or independence
What is iodine?
Iodine is an essential trace element needed for thyroid hormones. Iodized salt helped prevent iodine-deficiency goiter and developmental harm. Dental antiseptic research concerns topical povidone-iodine, which differs from swallowed nutritional iodide.
The forms that matter
| Form | What it is | Notes |
|---|---|---|
| Potassium iodide (KI) | Stable iodine salt | The standardized supplement/fortification form — predictable dose |
| Kelp/seaweed iodine | Iodine in seaweed matrix | Wildly variable content — the form behind most overdose case reports |
| Povidone-iodine (PVP-I) | Iodine complexed to polymer | Topical antiseptic — dental irrigation, pre-op rinses; not swallowed |
| Iodine tincture/Lugol’s | Elemental iodine solutions | High-dose, specific medical uses only |
Where does it come from?
Iodized salt (the vehicle that fixed the deficiency problem), dairy, eggs, seafood, and seaweed. In countries with iodization programs, dietary sufficiency is the norm.
What does the research show?
| Claim | Evidence | Dose | Verdict |
|---|---|---|---|
| Prevents deficiency disorders | Decades of public-health evidence | 150 mcg/day | Established |
| Fetal brain development (deficiency correction) | ALSPAC cohort: mild deficiency linked to lower childhood IQ | dietary status | Established risk |
| Benefits in iodine-sufficient people | No demonstrated benefit | — | Not shown |
| Oral/dental benefit from swallowed iodide | No trials | — | Not shown |
| Povidone-iodine periodontal add-on | Clinical trials of irrigation/rinse | topical | Supported — different molecule, different route |
What dose was studied?
| Goal | Dose | Notes |
|---|---|---|
| Sufficiency | 150 mcg/day | RDA; pregnancy 220 mcg |
| Toxicity threshold | 1,100 mcg/day | UL — thyroid dysfunction above this |
| Dental antisepsis | topical PVP-I | rinse/irrigation, not systemic |
Side effects
At RDA-adjacent doses: essentially none. The danger zone is chronic high intake: thyroid inflammation, a paradoxical return of goiter, unmasked hyperthyroidism (Jod-Basedow effect), and acne-like eruptions. This is why kelp supplements with unlabeled megadoses draw safety write-ups and potassium iodide doesn’t.
Drug interactions
- Antithyroid drugs (methimazole, PTU): iodine status directly modulates them
- Lithium: additive hypothyroid risk
- ACE inhibitors/ARBs + potassium-sparing diuretics: the potassium in KI matters only at high doses
- Radioactive iodine therapy: iodine saturation changes uptake (this is why KI is the nuclear-incident drug)
Who should not take it?
People with autoimmune thyroid disease (Hashimoto’s, which iodine can accelerate), active hyperthyroidism, and anyone stacking multiple iodine sources above the UL.
What the authorities say
NIH ODS, WHO, and the iodine-deficiency literature all say the same thing: sufficiency matters enormously, supplementation matters only for the deficient. No authority suggests dental uses for swallowed iodide.
What to know about iodine
Iodine helps meet nutritional needs but is not an established swallowed dental treatment. A 50 mcg amount provides one-third of daily need. Thyroid conditions, medication, and total iodine intake still matter; adequate intake is not a reason to assume extra iodine helps.
Frequently asked questions about Iodine
What does iodine do in the body?
One thing, done well: it's the raw material for thyroid hormones T3 and T4, which regulate metabolic rate, development, and temperature. There is no meaningful second function. When you see iodine in a non-thyroid product, it's either filling the label or borrowing topical-antiseptic credibility.
Is iodine good for teeth or gums?
Topically, yes. Povidone-iodine is a legitimate dental antiseptic used in periodontal irrigation and pre-surgical rinses, with trial support as an add-on. But that's antiseptic chemistry applied to the tissue. Swallowing 50 mcg of potassium iodide isn't the same thing and has no dental-outcome trials behind it.
How much iodine do adults need?
150 mcg/day (220 mcg in pregnancy). Iodized table salt provides it; a quarter teaspoon carries ~70 mcg. Deficiency is rare in iodized-salt countries and real where salt isn't iodized.
Can too much iodine be harmful?
Yes. The thyroid is exquisitely dose-sensitive. Chronic intake above ~1,100 mcg/day can trigger or unmask thyroid dysfunction (both under- and overactive), and kelp-type supplements are notorious for overshooting. 50 mcg, by contrast, is a third of the RDA; a gesture at sufficiency, not a real dose of anything.
Who benefits from iodine supplements?
People with confirmed deficiency or restricted intake: those who don't use iodized salt, strict vegans avoiding dairy, and pregnant women in low-iodine regions (where the stakes, fetal brain development, are highest). For the already-sufficient, extra iodine is excreted or stored, not used.
References
- [1]NIH Office of Dietary Supplements — Iodine fact sheet (RDA, UL, deficiency)
- [2]Bath SC et al. — Mild iodine deficiency in UK pregnancy and child IQ, ALSPAC cohort (Lancet, 2013)
- [3]Zimmermann MB et al. — Iodine deficiency disorders (Lancet review, 2008)
- [4]Mallik U et al. — Povidone-iodine as adjunct in periodontal therapy — clinical trial evidence
Products we reviewed containing Iodine
Based on recorded labels or seller-described formulas. Inclusion does not establish a match to the strains, preparations or amounts studied here; check each review's disclosure limits.