Iodine
Iodine is an essential component of the thyroid hormones thyroxine (T4) and triiodothyronine (T3). Iodine rarely occurs as the element but rather as a salt; for this reason, it is referred to as iodide and not iodine. Seafood, eggs, milk, and milk products are among the best sources of iodine.
Where to get it
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Research & evidence
Strong support Some support Weak or no supportColours show how well the sources back each point. The reason is next to each one.
NIH says goiter is usually the earliest clinical sign of iodine deficiency, and that iodine deficiency disorders result from inadequate thyroid hormone production secondary to insufficient iodine.
Strong evidenceStrong support. Stated plainly by NIH or an FDA label
Study details
NIH ODS: "Iodine deficiency disorders result from inadequate thyroid hormone production secondary to insufficient iodine." "Goiter is usually the earliest clinical sign of iodine deficiency."
Source: NIH ODS, Iodine — Health Professional Fact Sheet (Updated November 5, 2024), Iodine Deficiency View source
NIH says that during pregnancy and early infancy, iodine deficiency can cause irreversible effects.
Strong evidenceStrong support. Stated plainly by NIH or an FDA label
Study details
NIH ODS: "During pregnancy and early infancy, iodine deficiency can cause irreversible effects."
Source: NIH ODS, Iodine — Health Professional Fact Sheet (Updated November 5, 2024), Iodine Deficiency View source
NIH says chronic iodine deficiency may be associated with an increased risk of the follicular form of thyroid cancer.
Limited evidenceSome support. The source hedges (“may” or “associated with”)
Study details
NIH ODS: "Chronic iodine deficiency may be associated with an increased risk of the follicular form of thyroid cancer."
Source: NIH ODS, Iodine — Health Professional Fact Sheet (Updated November 5, 2024), Iodine Deficiency View source
Dosage
| Form | Amount |
|---|---|
| Any form | No standard dose is listed by our sources. |
Side effects
Well documented Reported (case reports, anecdotal or one study) None reportedThe circle shows how well documented an effect is, not how serious it is. A rarely reported effect can still be serious, so always read ‘When to stop’.
| Effect | Frequency | When to stop |
|---|---|---|
| Thyroiditis and thyroid papillary cancer (with excessive iodine intakes)Well documentedListed plainly by NIH, MSK or LiverTox | Not stated | Stop and talk to a doctor if you notice any unexpected or concerning symptoms. |
| Acute iodine poisoningWell documentedListed plainly by NIH, MSK or LiverTox | Rare; usually caused by doses of many grams | Stop and talk to a doctor if you notice any unexpected or concerning symptoms. |
Safety & interactions
Safety
Studies have also shown that excessive iodine intakes cause thyroiditis and thyroid papillary cancer. Cases of acute iodine poisoning are rare and are usually caused by doses of many grams. Responses to excess iodine and the doses required to cause adverse effects vary. Long-term intakes above the UL (upper limit) increase the risk of adverse health effects. Iodine supplements have the potential to interact with several types of medications.
Contraindications
NIH says studies have shown that excessive iodine intakes cause thyroiditis and thyroid papillary cancer. If you take antithyroid medication for hyperthyroidism, or take an ACE inhibitor, see Drug interactions.
Drug interactions
NIH describes antithyroid medications, such as methimazole (Tapazole), as used to treat hyperthyroidism. NIH says that taking high doses of iodine with antithyroid medications can have an additive effect and could cause hypothyroidism.
NIH says that taking potassium iodide with ACE inhibitors can increase the risk of hyperkalemia (elevated blood levels of potassium).
Established: stated plainly by an authoritative source. Documented: supported by case reports or trial data. Theoretical: based on mechanism, animal data, or a cautious listing. Always check with your pharmacist or prescriber.
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