Evidence explainerIodine (potassium iodide, kelp)
Switched to Sea Salt or Pink Salt? You May Have Quietly Dropped Your Main Iodine Source
Specialty salts are rarely iodized, and most salt in packaged food is not either. Here is where iodine actually comes from, how much adults need, and why more is not better.
Key takeaways
- Sea salt, kosher salt, Himalayan salt and fleur de sel are not usually iodized, and noniodized sea salt provides virtually no iodine [1].
- Iodized salt in the US is labeled at 45 mcg of iodine per gram, and a quarter teaspoon provides about 78 mcg [1].
- Most salt Americans eat comes from processed foods, and manufacturers almost always use noniodized salt [1].
- Adults need 150 mcg/day; seafood, dairy and eggs are among the best sources, so people who eat few of them may fall short [1].
- More is not better: the adult upper limit is 1,100 mcg/day, and some iodine-only supplements exceed it [1].
Safety at a glance
From our Iodine (potassium iodide, kelp) monograph. Published interactions and cautions only, each with its source.
Interactions
- Antithyroid medicines. High iodine doses with antithyroid drugs can have an additive effect and could cause low thyroid function.[1]
- ACE inhibitors. Potassium iodide with ACE inhibitors can raise the risk of high blood potassium.[1]
- Potassium-sparing diuretics. Potassium iodide with these diuretics can raise the risk of high blood potassium.[1]
Who should be careful
- High intakes. Too much iodine can cause some of the same problems as too little, including goiter, raised TSH and low thyroid function, and can also trigger an overactive thyroid or thyroid inflammation. The adult UL is 1,100 mcg/day; some iodine-only supplements exceed it.[1]
- Thyroid conditions. People with autoimmune thyroid disease, or who were previously iodine deficient, may have adverse effects at intakes considered safe for the general population.[1]
- Pregnancy. ODS reports that the American Thyroid Association and American Academy of Pediatrics advise 150 mcg/day of iodine before and during pregnancy and while breastfeeding, while noting a Spanish study linking ≥200 mcg/day supplements in pregnancy to raised TSH. Discuss amounts with a prenatal clinician.[1]
- Before you start. Talk to your pharmacist or clinician before adding this supplement, especially if you take prescription medicines, are pregnant or breastfeeding, or have a chronic health condition.[1]
The evidence, graded
Pulled from our monograph evidence tables. Grades follow our evidence-grading policy.
- Grade BImprovedCognitive scores in iodine-deficient childrenIodine slightly increased cognitive function vs placebo (SMD 0.19; 95% CI 0.04 to 0.34), high-certainty evidence. Weight showed little to no difference (low certainty).
- Grade BImprovedInformation processing and problem solving in moderately deficient schoolchildrenIodine improved iodine and thyroid status and performance on 4 of 7 cognitive and motor tests (information processing, fine motor skills and visual problem solving) vs placebo.
What the switch changes
Specialty salts such as sea salt, kosher salt, Himalayan salt and fleur de sel are not usually iodized, and the label will say so if they are [1]. Noniodized sea salt provides virtually no iodine [1].
Iodized table salt is a different story. US iodized salt is labeled at 45 mcg of iodine per gram, and a quarter teaspoon supplies about 78 mcg, roughly half the adult daily need [1].
One catch applies to everyone: most salt in the American diet comes from processed foods, and food makers almost always use noniodized salt [1]. So "I eat plenty of salt" does not mean "I get plenty of iodine".
Where iodine actually comes from
Dairy is variable. Its iodine depends on cattle feed and iodine-based sanitizers, and 59 samples of nonfat milk ranged from 38 to 160 mcg per cup [1]. Plant milks such as soy and almond contain relatively small amounts [1].
Seaweed is one of the richest sources, followed by fish and other seafood, eggs and dairy [1]. Typical amounts listed by ODS:
Who is most likely to fall short
Adults need 150 mcg a day, rising to 220 mcg in pregnancy and 290 mcg while breastfeeding [1]. ODS names vegans and people who eat few or no dairy products, seafood or eggs as groups who might not get enough, along with pregnant women [1].
Why it matters: a 2026 Cochrane review of iodine supplements in children rated a slight gain in cognitive function as high-certainty evidence [2], and in iodine-deficient Albanian schoolchildren, iodine improved scores on 4 of 7 cognitive and motor tests [4]. There is no evidence in our sources that extra iodine helps people who already get enough.
Why more is not better
The adult upper limit is 1,100 mcg/day [1]. Too much iodine can cause some of the same problems as too little, including goiter, raised TSH and an underactive thyroid, and it can also trigger an overactive thyroid or thyroid inflammation [1]. People with autoimmune thyroid disease, or who were previously deficient, can react to amounts that are fine for others [1].
That is the risk with iodine-only supplements and kelp tablets. Many multivitamins contain about 150 mcg, but iodine-only supplements often contain high doses, sometimes above the upper limit [1]. Seaweed itself ranges from 16 to 2,984 mcg of iodine per gram, and how much your body takes up varied from 61.5% to 101% depending on the seaweed and the person in one small study [1][3].
Potassium iodide, the usual supplement form, was absorbed almost completely (96.4%) in a small study [1][3]. If you take antithyroid medicine, an ACE inhibitor or a potassium-sparing diuretic, ODS advises discussing iodine intake with your clinician first [1]. Details are on the iodine monograph.
Quick answers
Is Himalayan pink salt a good source of iodine?
No. Specialty salts, including Himalayan salt, are not usually iodized unless the label says so [1].
Keep reading
Full monographs
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References
- [1]Iodine: Fact Sheet for Health Professionals. NIH Office of Dietary Supplements, 2024.
- [2]Iodine supplementation for preventing iodine deficiency disorders in children and adolescents. Cochrane Database Syst Rev, 2026.
- [3]Bioavailability of seaweed iodine in human beings. Cell Mol Biol (Noisy-le-grand), 2002.
- [4]Iodine supplementation improves cognition in iodine-deficient schoolchildren in Albania: a randomized, controlled, double-blind study. Am J Clin Nutr, 2006.