Supports thyroid function and prevents iodine deficiency. Iodine is the atom your thyroid builds its hormones around, and those hormones set your metabolic rate. Without enough coming in, hormone production has nothing to work with.
Reviewed March 2026
Public health figures for this ingredient, reported by the agencies that publish them, cited and dated.
US pregnant women, median 129 micrograms per litre
Across 2005 to 2010, US pregnant women had a median urinary iodine concentration of 129 micrograms per litre, which is below the range considered adequate during pregnancy.
Caldwell et al. (CDC Division of Laboratory Sciences), Thyroid 2013, NHANES 2005 to 2010; median urinary iodine 129 micrograms per litre in pregnant women, less than adequate. ↗Population figures from public health data. Context for the category, not a statement about any individual and not a claim about this product.
Source: NIH ODS + Zimmermann 2009 review
In a 24 week randomised double-blind placebo-controlled trial in 112 mildly iodine-deficient New Zealand adults aged 18 to 40, 150 micrograms of iodine a day as potassium iodate lowered thyroglobulin, a blood marker of iodine status, by 12 percent at 8 weeks, 20 percent at 16 weeks and 27 percent at 24 weeks compared with placebo. Median urinary iodine reached 168 micrograms per litre against 79 on placebo. TSH and free T4 stayed within normal range and did not change significantly.
These words describe the research, not the molecule's worth. Research strength is how much work stands behind one claim, and it is never a product score.
Iodine's role in thyroid hormone synthesis is well-established and universally accepted. Deficiency leads to serious health problems, and supplementation effectively corrects this.
Why these belong in the same formula. Each row says what the basis is, from settled biochemistry through to a trial that measured the pair.
The body builds thyroid hormones by attaching iodine atoms onto tyrosine residues, so tyrosine supplies the amino acid backbone while iodine supplies the atoms that make the finished hormone active. Together they are the two raw materials the thyroid draws on to keep normal hormone production running.
Iodine lets the thyroid assemble its storage hormone T4, and selenium-dependent deiodinase enzymes then convert that T4 into the active form T3, so one nutrient makes the hormone and the other switches it on. Selenium also runs the antioxidant enzymes that shield thyroid tissue from the reactive byproducts formed while it works with iodine.
Thyroid peroxidase, the iron-containing heme enzyme that attaches iodine to the growing hormone, needs adequate iron to do its job. When iron status runs low the thyroid uses iodine less efficiently, so the two nutrients support the same synthesis step.
Thyroid hormone receptors are built as zinc-finger proteins, so zinc forms part of the structure a cell uses to read the hormone's signal and act on it. That gives the hormone iodine helps assemble the receptor machinery it needs to work, which is why zinc sits among the nutrients thyroid function draws on.
Retinoid X receptors partner with thyroid hormone receptors on shared DNA response elements, and retinol status also influences pituitary TSH output. Iodine supplies the hormone's raw material while vitamin A governs how the finished signal is read.
Bladderwrack is a brown seaweed that concentrates iodide, so it contributes iodine on top of any added potassium iodide in the same formula. Total intake is the sum of both, which matters because thyroid hormone output responds to iodine at both low and high intakes.
Glucosinolate breakdown yields thiocyanate, a monovalent anion that competes with iodide for the sodium-iodide symporter that concentrates iodide in thyroid tissue. A generous iodine intake blunts this competition, which is why the two are worth flagging together in one formula.
Carnitine reduces entry of T3 and T4 into cell nuclei, so it acts as a peripheral counterweight to thyroid hormone signalling. Iodine supplies hormone synthesis while carnitine damps the tissue-level response, an opposing pair rather than a reinforcing one.
Withanolides nudge pituitary TSH signalling and raise circulating T4, which draws on the available iodide pool for hormone assembly. Adequate iodine keeps that raw material in place when the two are formulated together.
Guggulsterones increase iodine uptake by thyroid tissue and support conversion of T4 to the more active T3 in peripheral tissue. Iodine covers synthesis and guggul the activation step.
Table salt fortified with potassium iodide or potassium iodate is the main route by which iodine reaches most populations, because salt intake is steady and the carrier is cheap. Iodised salt appears repeatedly in the co-study record for this mineral for that reason. Iodine content of salt falls with heat, humidity and long storage, so the pairing is about delivery and stability rather than any added biological effect.
Iodide enters the thyroid on the sodium-iodide symporter, and nitrate, thiocyanate and perchlorate are all recognised competitive inhibitors at that transporter. High nitrate exposure therefore competes with iodide uptake, which matters most when iodine intake is already low. This is established transport pharmacology and is a direction to flag, not a benefit.
Ascorbate reduces molecular iodine to iodide quantitatively, which is the basis of a standard titration. In a liquid or a shared tablet matrix that reaction changes which iodine species is present. It is a formulation and analytical consideration, not a claim about absorption or thyroid function.
Activated charcoal adsorbs a wide range of co-ingested substances, and separating it from nutrients by several hours is standard practice for that reason. Iodide is a small anion delivered in small amounts, so co-ingestion is a plausible loss route. No study in this candidate set measured iodine absorption with charcoal, so the confidence stays short of established.
Clay binders are used precisely because they hold onto ions in the gut, which is a reason to space them away from micronutrient doses. Whether bentonite meaningfully reduces iodide uptake in people has not been measured in this candidate set. Flagged as a timing consideration rather than an established interaction for this specific mineral.
Conversion of riboflavin to its active flavin coenzymes is influenced by thyroid hormone status, and iodine is the element those hormones are built from. The relationship is described in nutritional biochemistry and runs in both directions. No trial in this candidate set gave the two together, so this is a mechanism note only.
Talk to a doctor before taking Iodine if any of these apply to you: Hyperthyroidism, Autoimmune thyroid conditions (Hashimoto's), Pregnancy (consult doctor), Kidney problems. These are flags to check first, not effects Iodine is known to cause.
Not medical advice. Show the label to your pharmacist.Iodine is built into thyroid hormones themselves, four atoms in one and three in the other. Without it, those hormones can't be made at all.
You absorb iodine almost entirely as iodide. A pump then pulls it into thyroid cells and concentrates it there, working uphill against the gradient.
Inside the gland an enzyme activates the iodide and attaches it to tyrosine spots on a big storage protein. That step uses hydrogen peroxide made right at the cell surface.
Two of those iodine-loaded pieces get joined together to form the hormone, which stays parked on the storage protein inside the follicle until it's released.
Most iodine is mined from a nitrate-rich ore in Chile or pulled out of salty underground water brought up with natural gas. It is turned into pure iodine, cleaned by turning it straight from solid to vapour, then made into a salt like potassium iodide for supplements. Kelp products skip all that and rely on the iodine the seaweed already contains, which is why kelp amounts have to be tested rather than assumed.
From a mineral source, then refined and usually bound to a carrier so the body can take it up.
Two commercial sources dominate: iodate-bearing caliche ore in northern Chile, and iodide-rich brine co-produced with natural gas in Japan and the United States. Kelp harvesting is a separate, botanical source used for seaweed-based products.
Ore is leached with water to bring iodate into solution; brine is treated to oxidise iodide to elemental iodine, which is then stripped from the liquid.
Iodate from ore is partly reduced with sulfur dioxide or bisulfite to produce elemental iodine; brine iodide is oxidised with chlorine or another oxidant to the same product.
Crude iodine is purified by sublimation, since iodine passes readily from solid to vapour, which separates it from salts and organic residues.
Purified iodine is converted to potassium iodide, sodium iodide, potassium iodate or calcium iodate, then assayed to a declared elemental iodine content.
Salts are diluted into carriers for tablets and premixes, dissolved for drops, or, for the botanical route, kelp is dried and milled with the native iodine content declared after testing.
The whole-food sources on file. A supplement closes the gap, it does not replace dinner.
A gram-for-gram figure (how much of each you would eat to match a dose) will appear here once it is sourced and reviewed. This page will not print a number it cannot cite.
These are the studies our verdict leans on, chosen from the 2,013 we read for Iodine. The full linked list is below.
7 sources behind our Iodine verdict: peer-reviewed studies and registered clinical trials. Every one links straight to PubMed, the journal, or ClinicalTrials.gov. Read them yourself.
Evidence surfaced via Semantic Scholar (Allen Institute for AI) and ClinicalTrials.gov. Ranked by study type and citation weight, not cherry-picked.
Read this carefully. These are 36,799 voluntary, unverified reactions reported to the FDA (openFDA). The number mostly reflects how popular Iodine is, not how risky it is. A report is not proof Iodine caused anything. It is a signal of what to watch for, nothing more.
Source: openFDA adverse-event reports. Voluntary reporting, not an incidence rate.
FDA Disclaimer: These statements have not been evaluated by the Food and Drug Administration. This information is for educational purposes only and is not intended to diagnose, treat, cure, or prevent any disease. Consult your healthcare provider before starting any supplement regimen.
