An essential mineral that the thyroid needs to make its hormones. Most studied in pregnancy, in children with low iodine, and for goiter.
Ask a doctor or pharmacist first if you:
Iodine is a trace element that the body needs to make thyroid hormones.[1] It is found in seaweed, fish, seafood, dairy, eggs and iodized salt.[1] Supplements usually contain potassium iodide or sodium iodide, and some contain kelp.[1]
The soil in some regions has little iodine, so crops grown there have little too. Iodized salt has greatly reduced iodine deficiency worldwide.[1]
Iodine supplements are mostly studied to prevent or correct iodine deficiency. Deficiency can cause goiter and can harm the growth and brain of a child.[1]
What the best studies found:
Some trials of iodine against infection and for wound healing used iodine antiseptics on the skin or in wounds, not supplements.[5][6]
At the usual intake, yes. Most people get less than the upper limit from food and supplements.[1] The US upper limit for adults is 1,100 µg a day, and the EU limit is 600 µg.[1][7]
Too much iodine can cause goiter, hypothyroidism, hyperthyroidism and inflammation of the thyroid.[1] People with autoimmune thyroid disease or iodine deficiency can react to amounts that are safe for most people.[1] Iodine can interact with antithyroid medicines, and potassium iodide with ACE inhibitors and potassium-sparing diuretics. Ask a doctor or pharmacist first if you have a thyroid disease or take these medicines.[1]
Iodine is a trace element. The thyroid gland uses it to make two hormones, thyroxine (T4) and triiodothyronine (T3).[1] A healthy adult holds 15 to 20 mg of iodine, and 70% to 80% of it is in the thyroid.[1]
When iodine is short, TSH stays high. The thyroid grows larger to trap more iodine from the blood. This enlarged thyroid is called a goiter.[1]
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Trials in pregnant women gave 150 to 225 µg of iodine a day as potassium iodide.[1][8] The US recommended intake for adults is 150 µg a day.[1]
A trial in children aged 10 to 13 with mild deficiency gave 150 µg a day.[9] In areas with iodine deficiency, trials gave one large dose by mouth, such as iodized oil: 100 mg to infants and 400 to 490 mg to children aged 6 to 17.[2][10][11] Trials for breast pain gave 1.5 to 6 mg of molecular iodine a day, above the US upper limit.[12][1]
The US recommended intake is 110 µg a day up to 6 months, 130 µg at 7 to 12 months, 90 µg at 1 to 8 years, 120 µg at 9 to 13 years and 150 µg from 14 years. It is 220 µg in pregnancy and 290 µg when breastfeeding.[1] WHO advises 250 µg in pregnancy and when breastfeeding.[1] EFSA, the EU food safety authority, sets 150 µg for adults and 200 µg in pregnancy and when breastfeeding.[13]
Most studies gave 0.1 to 0.25 mg a day, for 3 to 6 months.
The counts are study groups. A study group is one set of people in a study who took the same dose. One study can have several groups. These are amounts from studies, not advice for you.
25 of 117 study groups took iodine with something else. This shows what studies gave together, not what works together.
What studies used when they gave iodine for one goal, or to a group of people.
Each protocol describes what studies used, for one goal or for one group of people. It is not advice for you: talk to a doctor before you start a supplement.
12 questions in 4 groups. Open one for the short answer; each has its own page with the full answer and sources.
Seaweed is one of the best sources of iodine. Fish, seafood, dairy, eggs and iodized salt are also good sources.[1]
Iodine per serving in some foods:
Most fruits and vegetables contain little iodine, and the amount depends on the soil.[1] Sea salt, kosher salt and Himalayan salt are usually not iodized. In the US, most processed foods are made with salt that has no iodine.[1]
The thyroid grows larger, which is called a goiter. Goiter is usually the first sign of iodine deficiency.[1] Below about 10 to 20 µg a day, the thyroid cannot make enough hormone, and hypothyroidism follows.[1] In pregnancy, severe deficiency can harm the growth and brain of the fetus and can cause miscarriage and stillbirth.[1] Iodine deficiency is the most common cause of preventable intellectual disability in the world.[1]
People at higher risk:
In a 2-year trial, women on a Paleolithic-type diet, with no dairy and no table salt, had their urine iodine fall from 71 to 36 µg/L within 6 months.[14]
The need for iodine rises in pregnancy, from 150 to 220 µg a day in the US.[1] The American Thyroid Association advises 150 µg a day as potassium iodide for women who are pregnant, breastfeeding or planning a pregnancy.[1] Trials show that supplements raise the mother's iodine level, but reviews found no clear effect on the child's development.[3][4]
In children with low iodine, supplements give a small gain in some thinking skills.[2][15] A 2026 Cochrane review of 8 trials found a slight increase in cognitive function and likely fewer cases of hypothyroidism.[2] The trials studied children with mild or moderate iodine deficiency.[9][11]
In children with iodine deficiency, a 2026 Cochrane review found the effect on goiter very uncertain (2 trials, 432 children).[2] Without the trial at high risk of bias, iodine likely lowered the risk of goiter by 69% (1 trial, 230 children, moderate certainty).[2] In a program in Azerbaijan with severe deficiency, goiter was found in 99% of the children examined before iodized oil and in 2% of those examined four years after. This was not a randomized trial.[16]
A German trial included 1,024 adults with thyroid nodules, in a region with enough iodine. Iodine alone for 1 year did not shrink the nodules more than placebo (a 4.0% difference, not significant). Iodine with levothyroxine, a thyroid hormone medicine, shrank them by 17.3% more than placebo.[17]
Two small trials found less breast pain with high doses of iodine in women with fibrocystic breast disease, which causes lumpy and painful breasts.[1]
In a trial of 56 women, 65% had less pain after 6 months of iodine, against 33% with placebo.[1] In a trial of 111 women, 3 mg and 6 mg of molecular iodine a day reduced pain by month 3, but 1.5 mg did not. More than half of the women on 6 mg had a clear drop in pain.[12]
These doses are above the US upper limit of 1,100 µg a day, and they should only be used under a doctor's care.[1]
NIH ODS says that iodine appears to have a role in the immune response.[1] No trial found in PubMed searches tested iodine supplements taken by mouth against colds or other infections.
Some trials of iodine against infection and for wound healing used iodine antiseptics on the skin or in wounds. In one, a rinse of the wound with dilute povidone-iodine before closing it lowered infections after repeat hip and knee replacement from 3.4% to 0.4%.[5] In another, cadexomer iodine on chronic ulcers healed 58% to 66% of them in 12 weeks, against 20% with standard care.[6] These trials tested iodine on the body, not iodine supplements.[5][6]
No trial found in PubMed searches showed that iodine supplements help with weight loss. Iodine is needed for thyroid hormones, which control how fast the body uses energy.[1]
In a trial of 163 overweight or obese women in Morocco with iodine deficiency, TSH was 33% lower with 200 µg of iodine a day for 6 months than with placebo. The share of women with high total cholesterol fell to 21.5%, against 34.8% with placebo. The main outcomes of the trial were TSH and cholesterol.[18]
Too much iodine can cause hypothyroidism or hyperthyroidism.[1]
It protects the thyroid from radioactive iodine. The US FDA approved potassium iodide to block the thyroid and lower the risk of thyroid cancer in radiation emergencies that release radioactive iodine.[1] FDA advises 16 to 130 mg a day, by age, until the risk of exposure ends.[1]
After the Chernobyl accident in 1986, Poland gave potassium iodide widely, and thyroid cancer in children did not rise much. In Belarus and Ukraine, where it was not used, thyroid cancer in children and teenagers rose sharply.[1] People with iodine deficiency take up more radioactive iodine and have a higher risk.[1]
Yes. Too much iodine can cause goiter, hypothyroidism, hyperthyroidism and inflammation of the thyroid.[1] People with autoimmune thyroid disease or iodine deficiency can react to amounts that are safe for most people.[1] The US upper limit for adults is 1,100 µg a day, and the EU limit is 600 µg.[1][7]
Iodine supplements can interact with these medicines:[1]
People who take these medicines regularly should discuss their iodine intake with a doctor.[1] Amiodarone, a heart rhythm medicine, and iodine contrast media used in X-ray scans are also sources of extra iodine.[19]
Potassium iodide is the form that pregnancy trials and the American Thyroid Association use.[1] In a small study, people absorbed 96.4% of it.[1] Kelp and other seaweed supplements are less predictable, because the iodine content of seaweed varies widely.[1][20]
