Iodine is found in seafood, dairy products, eggs, seaweed, and iodized salt. These are the most reliable everyday sources, though the exact amount varies widely depending on the specific food. Most adults need 150 mcg of iodine per day, and a single serving of cod or a cup of milk can cover a large portion of that.
Why Your Body Needs Iodine
Iodine is the raw material your thyroid gland uses to build its hormones. The thyroid captures iodine from your bloodstream and incorporates it into two hormones, T3 and T4, which regulate your metabolism, heart rate, body temperature, and brain development. Without enough iodine, the thyroid can’t produce adequate hormones, and the gland may enlarge (a condition called goiter) as it works harder to compensate.
Many people with mild iodine deficiency don’t notice any symptoms. When levels drop further, signs of an underactive thyroid can appear: fatigue, unexpected weight gain, dry skin, constipation, a slow heartbeat, and depression. During pregnancy, iodine deficiency is more serious. It can cause brain damage in the developing baby, congenital disorders, miscarriage, or stillbirth. Pregnant women need 220 mcg daily, and breastfeeding mothers need 290 mcg.
Seafood: The Richest Natural Source
Fish and shellfish concentrate iodine from seawater, making them the most dependable natural sources. A 3-ounce serving of baked cod provides about 146 mcg, which alone nearly meets the full daily requirement for an adult. Pacific cod delivers a similar amount at 144 mcg per 4-ounce raw serving.
Other seafood provides iodine too, though amounts vary. Raw shrimp contains about 18 mcg per 4-ounce serving, far less than cod. Breaded and fried shrimp drops even lower, to around 8.5 mcg per 3-ounce serving. The general pattern holds: white fish tends to be higher in iodine than shellfish, and preparation methods can affect the final numbers.
Seaweed: Extremely High but Unpredictable
Seaweed is the most concentrated food source of iodine on the planet, but the amounts swing dramatically by type. Nori, the thin sheets used in sushi rolls, provides about 116 mcg per 2-tablespoon serving of flaked dried seaweed. That’s a reasonable amount, roughly comparable to a serving of cod.
Other varieties are in a completely different league. Wakame contains around 5,049 mcg in a 30-gram serving, and kombu packs a staggering 22,033 mcg in just 5 grams. Those numbers are far above the tolerable upper limit of 1,100 mcg per day for adults. Regularly eating kombu or wakame in large amounts can actually overwhelm the thyroid and cause dysfunction. If you enjoy seaweed, nori is the safest everyday choice.
Dairy, Eggs, and Bread
In many Western diets, dairy products are a primary source of iodine. This is partly because iodine-containing solutions are used to sanitize milking equipment, and partly because cattle feed is often supplemented with iodine. A cup of milk typically provides a meaningful share of your daily needs, and yogurt follows a similar pattern.
Eggs contain iodine as well, concentrated mostly in the yolk. Bread is a less obvious source. Some commercial bakeries use iodate as a dough conditioner, and when they do, the iodine content of the bread is significantly higher than in loaves made without it. USDA researchers found enough variation that they created separate database entries for breads made with and without iodate conditioners. There’s no way to tell from the label whether your bread contains it, so this isn’t a source you can count on deliberately.
Iodized Salt vs. Sea Salt
Iodized table salt is one of the most important public health interventions of the past century. In the U.S. and Canada, iodized salt contains roughly 40 to 85 mcg of iodine per gram. A quarter teaspoon (about 1.5 grams) gives you somewhere around 60 to 130 mcg, a significant chunk of your daily target.
Sea salt, by contrast, is nearly iodine-free unless it’s been specifically fortified. Testing of unfortified sea salt samples found less than 2 mcg per gram. If you cook primarily with sea salt, pink Himalayan salt, or kosher salt, you’re getting almost no iodine from your salt. This is one of the most common blind spots in otherwise healthy diets. Switching to iodized salt for even some of your cooking can make a real difference.
Plant Foods Are Unreliable Sources
Fruits, vegetables, grains, and nuts are generally poor sources of iodine. The iodine content of any plant depends almost entirely on how much iodine was in the soil where it grew, and that varies enormously by region. On average, an 80-gram serving of fruits or vegetables provides only about 3 mcg of iodine. Nuts offer around 5 mcg per 25-gram serving. Bread (when no iodate conditioner is used) provides roughly 10 mcg per 70-gram serving.
Online sources frequently claim that prunes, strawberries, cranberries, potato skins, and navy or kidney beans are rich in iodine. Researchers who reviewed these claims found them to be inaccurate. If you eat a plant-based diet without seaweed, iodized salt, or a supplement, you are at elevated risk for iodine deficiency. This is one of the nutrients that genuinely requires attention on a vegan diet.
Foods That Interfere With Iodine
Some foods contain compounds called goitrogens that can block iodine from reaching your thyroid. Cruciferous vegetables like kale, cauliflower, and turnips contain a compound that breaks down into thiocyanate, which competes with iodine for entry into thyroid cells. Soy products contain isoflavones that can inhibit thyroid hormone production in people who are already low in iodine. Cassava, a staple root vegetable in parts of Africa, contains a compound that also converts to thiocyanate in the body.
None of these foods are dangerous if your iodine intake is adequate. The interference only becomes a real problem when someone is already deficient and eating large amounts of these foods regularly. Cooking reduces goitrogen content substantially, and simply using iodized salt in your meals is usually enough to offset the effect.
Unexpected Sources: Food Dyes
A cherry-red food dye called erythrosine (FD&C Red No. 3) contains iodine and shows up in decorating gels, candies, glacé cherries, some ice creams, and popsicles. However, the iodine in this dye has low bioavailability, meaning your body doesn’t absorb it efficiently. It’s not a meaningful contributor to your iodine status, so it’s not worth factoring into your intake.