Iodine: what it does, how much you need, and how much is too much
By Vita · fact-checked against NIH ODS
Vita is Vitaminico's AI nutrition coach. Every number here is checked against the NIH Office of Dietary Supplements; these pages have not yet been reviewed by our registered dietitians.
A trace mineral your thyroid needs to make the hormones that run your metabolism.
Iodine: key facts
- Everyday need (RDA/AI)
- 150 mcg for all adults (220 mcg in pregnancy, 290 mcg in lactation)
- Safe upper limit (UL)
- 1,100 mcg
- Measured in
- mcg
- Best foods
- Iodized salt, seaweed (kelp, nori, wakame), fish and other seafood, dairy products, eggs
Adult values from the NIH ODS Iodine fact sheet. Needs differ in pregnancy, lactation and childhood.
What does iodine do?
Your thyroid gland uses iodine to make thyroid hormones (T3 and T4), which control your metabolism — how your body turns food into energy. These same hormones are essential for normal bone and brain development before birth and during infancy, which is why needs rise in pregnancy. Iodine may also play a role in immune function. The body doesn't make iodine, so it has to come from food or supplements. Adults need 150 mcg per day.
Why you might be low on iodine
- You use specialty salts (sea salt, kosher, Himalayan, fleur de sel) instead of iodized table salt — these usually contain little or no iodine
- You're vegan or eat few or no dairy products, seafood, or eggs, which are the main dietary sources
- You're pregnant or breastfeeding — needs jump to 220 mcg and 290 mcg per day, roughly 50% more
- You live in a region with iodine-poor soil (mountainous areas like the Himalayas, Alps, or Andes) and eat mostly local produce
- You follow a low-salt diet and don't get iodine from other foods
Signs of low iodine
These are common signals, not a diagnosis — a blood test and your clinician confirm a real gap.
- Goiter — swelling or enlargement of the thyroid at the base of the neck, usually the earliest sign
- Fatigue, sluggishness, and feeling cold (signs of an underactive thyroid)
- Unexplained weight gain
- Dry skin and constipation
- Elevated TSH (thyroid-stimulating hormone) on a blood test
- In pregnancy, severe deficiency can harm the baby's brain development and is linked to lower child IQ
Best food sources of iodine
| Food | Typical amount |
|---|---|
| Cod, baked, 3 ounces | 146 mcg (97% DV) |
| Seaweed (nori), dried, 2 tablespoons flaked (5 g) | 116 mcg (77% DV) |
| Greek yogurt, plain, nonfat, ¾ cup | 87 mcg (58% DV) |
| Milk, nonfat, 1 cup | 84 mcg (56% DV) |
| Iodized table salt, ¼ teaspoon | 78 mcg (52% DV) |
| Egg, hard-boiled, 1 large | 31 mcg (21% DV) |
| Shrimp, cooked, 3 ounces | 13 mcg (9% DV) |
How much iodine is too much?
The tolerable upper intake level (UL) for adults is 1,100 mcg per day. Both too little and too much iodine can cause thyroid dysfunction; use of iodized salt has largely eliminated deficiency in many countries.
The safe upper limit for adults is 1,100 mcg per day, and regularly exceeding it can paradoxically cause many of the same problems as too little — goiter, an underactive or overactive thyroid, and thyroid inflammation. High-dose kelp or iodine supplements and frequent seaweed are the usual culprits, and people with an existing thyroid condition can react even at intakes considered safe for most people.
Stacking a multivitamin, a single supplement and fortified foods adds up faster than it looks — run your full dose through the free Supplement Safety Checker before adding anything new.
Iodine FAQ
Does sea salt or Himalayan salt give me iodine?
Usually not. Specialty salts like sea salt, kosher salt, Himalayan salt, and fleur de sel typically contain little or no iodine. Only salt labeled 'iodized' reliably provides it — check the label. Most salt in processed foods is also non-iodized.
Do I need an iodine supplement?
Most people in the U.S. and Canada get enough from food, and overt deficiency is uncommon. The main exceptions are people who are pregnant, breastfeeding, or planning pregnancy — major medical groups suggest a 150 mcg/day supplement for them — and vegans who avoid dairy, seafood, and eggs. Talk to your doctor before supplementing.
Can I get too much iodine from seaweed?
Yes. Seaweeds vary enormously in iodine (from about 16 to nearly 3,000 mcg per gram), and kelp/kombu can be especially high. Eating a lot regularly, or taking kelp supplements, can push you over the upper limit and disrupt thyroid function.
Source
Every RDA/AI, upper limit and unit on this page is drawn from the NIH Office of Dietary Supplements Iodine fact sheet ›.
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Educational, not medical advice. The upper limits shown are Tolerable Upper Intake Levels for healthy adults from all sources combined; needs differ in pregnancy, lactation, childhood and with some conditions or medications. This page does not diagnose a deficiency or set your dose — talk to your clinician before starting any high-dose supplement.