Seaweed is the food highest in iodine. Dried nori averages 2,317 micrograms per 100 grams in the USDA, FDA and NIH iodine database, and kelp can run far higher. Among everyday foods, white fish leads: baked cod carries 172mcg per 100g, more than the 150mcg adult requirement in one portion. Dairy and eggs come next.
Most iodine lists stop there. The more useful part is why the numbers swing so much. Iodine is the rare nutrient where farming practice and food processing matter as much as the food itself. A glass of milk in winter carries more than the same glass in summer. A slice of American white bread can carry over 300 times the iodine of the loaf next to it, depending on one ingredient. The ranking below is the starting point. The sections after it explain the swings.
The short version
- Dried seaweed tops every list, with nori at 2,317mcg per 100g.
- Baked cod gives 172mcg per 100g. Baked salmon gives 13mcg.
- Adults need 150mcg a day in the US and 140mcg in the UK.
- Unfortified plant milks carry 1.7% of the iodine in cows' milk.
- Iodised salt is hard to find in UK supermarkets, so food choice does the work.
What food is highest in iodine, ranked per 100g
Every figure below comes from the USDA, FDA and ODS-NIH Database for the Iodine Content of Common Foods (Release 3, March 2023), per 100 grams. The three agencies built it specifically for iodine, which makes it the best reference available. These are US foods, cooked unless marked raw. Single foods were cooked without salt, so a pinch of iodised salt would add to any row.
| Food | Iodine (mcg per 100g) |
|---|---|
| Nori seaweed, dried | 2,317 |
| White bread made with iodate dough conditioner | 592 |
| Haddock, raw | 227 |
| Cod, baked | 172 |
| Oysters, wild, cooked | 109 |
| Fish sticks, oven-cooked | 67 |
| Eggs, hard-boiled | 61 |
| Greek yogurt, plain, nonfat | 51 |
| Cheddar cheese | 46 |
| Alaska pollock, raw | 44 |
| Milk, reduced fat (2%) | 36 |
| Milk, whole | 34 |
| Yogurt, whole milk, plain | 32 |
| Bluefin tuna, cooked | 23 |
| Pasta boiled in iodised salt water | 22 |
| Beef liver, pan-cooked | 16 |
| Shrimp, precooked | 15 |
| Salmon fillet, baked | 13 |
| Tuna, canned in water | 9.4 |
| Beef mince, pan-cooked | 7.5 |
| Spinach, boiled | 3.9 |
| Whole-wheat bread, no iodate | 1.9 |
| Chicken breast, roasted | 1.2 |
| Almond drink | 0.4 |
| Brown rice, cooked | 0 |
| Kidney beans, canned | 0 |
The pattern is blunt. The sea and the dairy aisle supply nearly all of it. Meat, grains, nuts and most vegetables sit in single figures or at zero. The database documentation puts this down to seaweed and saltwater fish concentrating iodine from seawater, while crops carry whatever their soil happens to hold.
In practical terms, a 150g fillet of baked cod works out around 258mcg. That clears the day on its own. A 250ml glass of 2% milk lands near 90mcg. The same glass of almond drink gives about one.
Seaweed: the richest source, and the hardest to dose
Seaweed tops the chart, and it also has the widest range of any food on it. A 2004 study in Thyroid tested 12 species of edible seaweed bought in the US or supplied by harvesters. Iodine ran from 16 micrograms per gram in nori to over 8,165 micrograms per gram in one sample of processed kelp granules sold as a salt substitute.
Run that top number through the arithmetic. One gram of those granules holds more than seven times the 1,100mcg daily upper limit for adults. The same paper found that two Namibian kelps ranged from 514 micrograms per gram in sun-bleached blades to 6,571 in freshly cut young ones. Two kelps from the same coast, and a twelvefold gap between the extremes. The authors also noted that iodine leaches into cooking water and can be lost in humid storage, and that some seaweed dishes may exceed the upper limit.
Nori sits at the gentle end. At 2,317mcg per 100g, that's roughly 23mcg per gram of dried sheet. Sushi is a reasonable way to eat iodine. A daily spoonful of kelp powder is a gamble, because nobody can tell you which end of the range is in the jar.
Why white fish beats salmon by thirteen to one
"Eat more fish" is the standard iodine advice, and the table shows why it needs an edit. Baked cod carries 172mcg per 100g and raw haddock 227. Baked salmon carries 13. Canned tuna in water carries 9.4, and precooked shrimp 15.
The database records the gap without explaining it, so we won't invent a reason. What matters is that it holds across the salmon entries: raw sockeye at 14, canned pink at 15, raw pink at 26. Oily fish earns its place for other reasons. If iodine is the goal, the lean white fish (cod, haddock, pollock) and oysters do the job, and fish fingers made from them still land at 67.
Milk: the main source for most people, with a seasonal catch
Milk is the iodine story in Britain. A 2017 study in the British Journal of Nutrition called UK milk the principal dietary iodine source. The iodine is partly a farming by-product. The US database documentation lists iodine supplements given to animals and iodine-based sanitisers among the reasons levels vary.
That makes milk inconsistent. A 2024 meta-analysis covering 34 countries found milk iodine ranging from 5.5 to 49.9 micrograms per 100g, with a median of 17.3. Winter milk ran about 6 micrograms per 100g higher than summer milk. Conventional milk ran about 6 higher than organic, though that gap was only significant in summer.
The plant-milk swap is the bigger drop. The 2017 UK study tested 47 milk-alternative drinks. The 44 unfortified ones had a median of 7.3 micrograms per kilo, 1.7% of the 438 measured in winter conventional cows' milk. Three of the 47 were fortified with iodine. If you've moved to oat or almond and eat little fish, that's the gap worth checking, and our iodine deficiency symptoms post covers what it can look like.
Salt and bread: the hidden iodine most UK diets don't get
In the US, iodised table salt averages 5,213mcg per 100g, about 52mcg per gram. Boil pasta in it and the pasta picks up 22mcg per 100g, against 0.3 for pasta cooked plain.
The UK picture is different. A survey of 77 UK supermarkets found iodised salt on the shelf in 32 of them. Weighted by market share, availability was 21.5%. The main UK brand carried 11.5mg per kilo, which is 11.5mcg per gram, roughly a fifth of the US average. The authors concluded that table salt is unlikely to add meaningful iodine to UK diets, and that UK intake depends on food choices.
Bread is the odd one. Some US bakeries use potassium or calcium iodate as a dough conditioner, and the database lists those loaves separately because the difference is so large: 592mcg per 100g of white bread with it, 1.8 for white bread without. Check the ingredient list for "iodate". It's the only way to know.
How to get 150mcg of iodine a day from food
Using the USDA iodine database figures above, any one of these covers most or all of the US requirement:
- A 150g fillet of baked cod, at around 258mcg.
- A 250ml glass of 2% milk plus 100g of Greek yogurt, at around 140mcg.
- A 250ml glass of 2% milk, 40g of cheddar and 50g of hard-boiled egg, at around 140mcg.
- A sushi meal with a couple of nori sheets, which varies too much to put a number on.
The hard case is the man who eats no fish, little dairy and drinks unfortified plant milk. Looking down the table, his diet sits almost entirely in the single-figure rows. For him, a fortified plant drink or a supplement is the practical fix. For the other trace mineral that tracks soil, see what food is highest in selenium.
Where Fireblood fits
Fireblood carries 75mcg of iodine from sea kelp. That's half the US requirement and just over half the UK one, so the other half still has to come from your plate. If you eat fish or dairy most days, the table says that's easy. If you eat neither, it's the half worth planning for.
The difference between our kelp and a jar of kelp granules is the label. Ours is a fixed 75mcg per scoop. The 2004 seaweed study shows why that matters more with iodine than with almost any other nutrient.
Fireblood contains 75mcg of iodine from sea kelp alongside 38 other nutrients, including 25mcg of selenium. See the full formula.
Header photo: drying kelp in Hokkaido by Marie-Sophie Mejan, Wikimedia Commons, CC BY 4.0.
