The richest sources of iodine are seafood, dairy products, eggs, and iodized salt. Most adults need 150 mcg of iodine per day, and a single cup of milk or a serving of yogurt gets you more than halfway there. But iodine levels vary wildly between foods, and some sources contain hundreds of times more than others.
Seaweed: The Most Concentrated Source
Seaweed contains far more iodine than any other food, but the amount depends dramatically on the type. Kombu (a form of kelp) is in a league of its own. Dried kombu contains roughly 2,100 to 6,800 mg of iodine per kilogram, meaning even a small piece used to flavor soup can deliver thousands of micrograms. That’s well above the 150 mcg most adults need daily, and it can easily push past safe limits if you eat it regularly.
Wakame is much more moderate. Dried wakame contains about 220 to 280 mg/kg, and once cooked, the concentration drops to around 27 to 31 mg/kg. Nori, the thin sheets used to wrap sushi, is the mildest of the common seaweeds at just 9 to 20 mg/kg when dried. If you’re looking for a seaweed you can eat often without worrying about overdoing it, nori is the safest bet.
Dairy Products
Milk is one of the most reliable everyday sources of iodine. A single cup of whole milk provides about 82 mcg, and reduced-fat or skim milk delivers slightly more, around 84 to 88 mcg per serving. The iodine comes partly from iodine-containing solutions used to sanitize milking equipment and partly from iodine in cattle feed.
Yogurt falls in a similar range. A serving of plain Greek yogurt provides 55 to 87 mcg depending on the fat content, with nonfat versions tending to land higher. Even flavored varieties like strawberry or vanilla Greek yogurt deliver around 70 to 86 mcg. Frozen yogurt is lower, at roughly 53 mcg per serving. For people who drink milk or eat yogurt daily, dairy alone can cover a large share of your iodine needs.
Eggs
A single large raw egg contains about 25 mcg of iodine, with nearly all of it concentrated in the yolk. Hard-boiled eggs provide around 31 mcg, and scrambled eggs come in slightly higher at about 47 mcg per serving. The variation between individual eggs can be significant, ranging from 14 to 58 mcg for a fresh egg, because iodine content depends on what the hens were fed.
Fish and Shellfish
Ocean fish and shellfish are naturally rich in iodine because seawater contains dissolved iodide. Cod, shrimp, and tuna are commonly cited as good sources, with cod typically providing the highest amounts among popular fish. Freshwater fish contain less iodine than their saltwater counterparts. The exact amount in any piece of fish depends on the species, where it was caught, and how it was prepared.
Iodized Salt
Iodized table salt is the single most important fortified source worldwide. The World Health Organization defines adequately iodized salt as containing 15 to 40 parts per million of iodine. In practical terms, about half a teaspoon of iodized salt provides roughly 75 mcg. This fortification program exists specifically because many diets would otherwise fall short.
One important distinction: sea salt, kosher salt, and pink Himalayan salt are generally not iodized unless the label says otherwise. If you’ve switched away from regular table salt, you may be getting far less iodine than you think. The same goes for the salt used in most processed and restaurant foods, which is typically not iodized.
Bread Made With Iodate Dough Conditioners
This one surprises most people. Some commercial bread contains a dough conditioner called calcium or potassium iodate, and it makes an enormous difference. USDA data shows that a white hamburger bun without this conditioner contains about 2.2 mcg of iodine per 100 grams. The same bun made with an iodate conditioner jumps to 1,196 mcg per 100 grams. Whole wheat bread shows a similar gap: 2.8 mcg without the conditioner versus 618 mcg with it.
There’s no easy way to know which brands use iodate dough conditioners, since it’s listed in the ingredients but not highlighted on the front label. This is one reason iodine intake can vary so much between people eating seemingly similar diets.
Fruits, Vegetables, and Grains
Plant foods are generally poor sources of iodine. Whatever iodine they contain comes from the soil they grew in, and iodine levels in soil vary enormously by region. Mountainous areas, river valleys that have flooded repeatedly, and inland regions far from the ocean tend to have the most depleted soils. This geographic variability means you can’t reliably count on produce for iodine, no matter how many servings you eat.
Non-Food Sources of Iodine
Iodine also shows up in medical settings. Iodinated contrast media, the dyes used during CT scans and certain X-rays to make blood vessels and organs visible, contain substantial amounts of iodine. These are given as injections, oral drinks, or rectally. Povidone-iodine, the brown antiseptic used to clean wounds and surgical sites, is another common source. Some supplements, particularly those containing kelp, can also deliver very high doses.
How Much You Need
Most adults need 150 mcg of iodine per day. Children need less: 90 mcg for ages 1 through 8, and 120 mcg for ages 9 through 13. The requirement increases during pregnancy to 220 mcg and rises further during breastfeeding to 290 mcg, because iodine is critical for fetal and infant brain development.
Your thyroid gland uses iodine as a raw building block for its hormones. Thyroid cells actively pull iodide from your blood using a specialized transport system, then an enzyme attaches the iodine atoms to a protein to create thyroid hormones. These hormones regulate your metabolism, heart rate, body temperature, and brain function. Without enough iodine, the thyroid can’t produce adequate hormones, leading to fatigue, weight gain, and in severe cases, a visible swelling of the thyroid called a goiter.
Too Much Iodine Is Also a Problem
While deficiency gets most of the attention, excess iodine can also disrupt thyroid function. This is most relevant for people eating large amounts of kombu or kelp supplements. A single serving of dried kombu can easily deliver 10 to 40 times the daily recommendation. The upper limit for adults is 1,100 mcg per day, and exceeding it regularly can cause either an overactive or underactive thyroid, depending on your individual susceptibility. People with pre-existing thyroid conditions are particularly sensitive to iodine fluctuations in either direction.