Most vegetables contain very small amounts of iodine, typically less than 2 mcg per 100 grams. That’s a fraction of the 150 mcg adults need daily. While vegetables contribute to your overall iodine intake, they’re not a reliable primary source on their own, with the notable exception of seaweed.
Vegetables With the Most Iodine
Among common land vegetables, spinach and potatoes top the list, but even these provide modest amounts. Here’s how the highest-iodine vegetables compare, based on USDA data measured per 100 grams:
- Raw spinach: 6.0 mcg
- Mashed potatoes (from fresh): 6.2 mcg
- Boiled spinach: 3.9 mcg
- Raw celery: 1.6 mcg
- Raw baby carrots: 1.4 mcg
- Boiled collard greens: 1.4 mcg
- Sweet potato, baked: 1.3 mcg
- Leaf lettuce: 1.2 mcg
- Baked potato with peel: 1.0 mcg
- Boiled okra: 1.0 mcg
To put this in perspective, you’d need to eat roughly 2.5 kg (about 5.5 pounds) of raw spinach to hit 150 mcg of iodine from that source alone. Most other vegetables fall below 1 mcg per 100 grams. Broccoli, cauliflower, green beans, corn, peppers, and tomatoes all clock in at 0.3 to 0.6 mcg per 100 grams.
The mashed potatoes figure (6.2 mcg) is worth noting because it likely reflects added milk or butter during preparation, both of which contain meaningful iodine. A plain baked potato with peel provides just 1.0 mcg.
Seaweed Is the Exception
Dried nori, a type of seaweed commonly used in sushi, contains roughly 2,320 mcg of iodine per 100 grams. That’s hundreds of times more than any land vegetable. Other seaweed varieties like kelp and wakame can contain even higher concentrations. If you’re specifically trying to boost iodine through plant foods, seaweed is the most potent option available.
A single sheet of nori weighs about 2.5 grams, delivering around 58 mcg of iodine, which covers about 39% of the adult daily recommendation in one small piece. This makes seaweed both powerful and something to be mindful of. The upper safe limit for adults is 1,100 mcg per day from all sources, and certain seaweed products can push you toward that threshold quickly.
Why Iodine Levels Vary So Much
The iodine content of any vegetable depends heavily on the soil it was grown in. Soil iodine comes primarily from ocean deposits carried inland by rain, fog, and spray. You might expect coastal farms to produce higher-iodine crops, and that pattern does hold on smaller landmasses like New Zealand and Ireland. But in larger continental countries, the relationship breaks down. In China, for example, soil type, organic matter, and climate are more important predictors of soil iodine than proximity to the coast.
Once iodine reaches the soil, only about 4 to 10% of it remains in a water-soluble form that plant roots can absorb. The rest binds tightly to organic matter and minerals. Iodine also evaporates from soil over time, with the rate depending on soil type. All of this means the same variety of spinach grown in two different regions could have meaningfully different iodine levels. The USDA figures represent averages across multiple samples, but your particular bunch of spinach could be higher or lower.
Some researchers have explored fortifying vegetables by applying iodine-containing fertilizers, particularly through foliar spraying (applying a solution directly to plant leaves). This approach has shown promise for increasing iodine content in crops, but it’s not standard agricultural practice in most countries.
Cruciferous Vegetables and Iodine Use
Broccoli, kale, cabbage, cauliflower, and Brussels sprouts belong to the Brassica family, sometimes called cruciferous vegetables. These contain natural compounds that can interfere with how your thyroid absorbs and uses iodine. Specifically, these compounds can block the mechanism that transports iodine into thyroid cells and may reduce the activity of enzymes the thyroid needs to make its hormones.
Animal studies have shown that kale, for instance, lowered iodine accumulation in the thyroid compared to control diets. A human case report linked heavy raw broccoli consumption to thyroid dysfunction. However, a comprehensive systematic review of the research concluded that eating normal amounts of cruciferous vegetables, especially when your iodine intake is adequate, poses no meaningful risk to thyroid function. The concern applies mainly to people who eat very large quantities of raw cruciferous vegetables while already consuming too little iodine.
How Much Iodine You Actually Need
Adults need 150 mcg of iodine per day. During pregnancy, that rises to 220 mcg (the WHO recommends 250 mcg), and during breastfeeding it increases to 290 mcg. These higher requirements support fetal and infant brain development.
Given how little iodine vegetables provide, most people get the bulk of their iodine from other sources. Iodized salt is the most common one: half a teaspoon of iodized salt contains roughly 71 mcg. Dairy products contribute significantly because iodine-based sanitizers are used in milk processing, and dairy cows often eat iodine-supplemented feed. Eggs, fish, and shellfish are also reliable sources.
If you eat a varied diet that includes iodized salt and some dairy or seafood, vegetables act as a small supplemental source rather than your main supply. But if you follow a vegan diet, avoid iodized salt, or eat mostly unprocessed foods, those small contributions from spinach, potatoes, and other vegetables become more meaningful, and a supplement or regular seaweed intake may be worth considering to close the gap.