Iodine in Plant Based Foods

Seaweed can provide substantial iodine, but reliability is a concern. Iodine content in seaweed varies dramatically based on the iodine concentration of the ocean water where it grows — the same species can range from 100,000–250,000 µg per 100g between locations, a 2.5-fold variation. Additionally, some seaweeds (hijiki, sea vegetables) accumulate inorganic arsenic from seawater, which poses a safety concern with regular consumption.

The Recommended Dietary Allowance (RDA) for iodine is 150 µg per day for adults of all ages. Pregnant individuals require 220 µg per day, and lactating individuals require 290 µg per day due to increased transfer to the fetus and infant. The Tolerable Upper Intake Level (UL) is 1,100 µg per day for adults — high enough that most whole foods pose no risk, but excessive seaweed consumption (especially kelp supplements or heavy daily seaweed eating) can easily exceed this threshold.

Nori (dried seaweed sheets used for sushi) contains approximately 3,700 µg of iodine per 100g of raw dried nori, and about 2,800 µg per 100g when roasted (the more common commercial form). A typical single nori sheet weighs roughly 3g and provides approximately 80–110 µg of iodine — enough to cover a meaningful portion of the daily RDA (150 µg). However, iodine content varies significantly depending on the growing region and harvest season, so consistency cannot be guaranteed.

Yes — but plant based eaters must be intentional. Plant based diets can easily achieve the 150 µg RDA through one of three strategies: (1) using iodized salt in cooking and seasoning, which is reliable and incidental (a teaspoon of iodized salt provides ~450 µg); (2) consuming modest amounts of seaweed (1–2 nori sheets, or small amounts of wakame in broth), though this requires monitoring due to variability; or (3) taking a plant based iodine supplement (150 µg daily), which eliminates guesswork.

Iodine content in plant foods is relatively stable during normal cooking methods like boiling, steaming, and baking. The primary determinant of iodine content in vegetables, beans, and grains is the iodine concentration of the soil in which they were grown — if soil is iodine-poor, the cooked or raw food will have low iodine content regardless. However, iodized salt loses iodine when heated above 180°C (356°F), so iodized salt should be added after cooking rather than used in high-heat cooking or baking.