Iodine in Plant-Based Foods

Seaweed is the richest source — dried kelp/kombu contains up to 150,000 µg per 100g, though variability is extreme (100,000–250,000 µg/100g depending on growing region). Other seaweeds like hijiki (~40,000 µg/100g), dulse (~7,200 µg/100g), and wakame (~9,300 µg/100g) are also rich but require careful management due to arsenic contamination in some varieties and iodine variability. For more moderate, safer whole-food sources, navy beans (~32 µg/100g), white beans (~28 µg/100g), and potatoes (~60 µg/100g) are reliable. Most other plant foods have low iodine content unless grown in iodine-rich soil. See the ranking tool above to explore the full dataset and discover options suited to your dietary preferences.

Iodine is an essential trace mineral that serves critical roles in metabolism and development. It is the central structural component of thyroid hormones (T3 and T4), which regulate metabolic rate, energy production, body temperature, growth, and development. During pregnancy and lactation, adequate iodine is absolutely essential for fetal brain development and early childhood cognitive development — even mild maternal iodine deficiency can impair offspring IQ and learning capacity. Iodine also supports immune function and antioxidant defences. Without adequate iodine, the thyroid becomes enlarged (goiter) and thyroid hormone production is impaired, leading to hypothyroidism, fatigue, weight gain, cold intolerance, and in severe cases, cretinism (a preventable cause of intellectual disability).

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. Plant-based eaters should monitor intake carefully if consuming seaweed regularly, or instead rely on iodized salt combined with whole foods, or a plant-based iodine supplement.

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. The key difference from omnivorous diets is that plant-based eaters need to plan for iodine, whereas meat-eaters receive iodine incidentally through animal products. With intentional planning, plant-based diets easily meet iodine requirements.

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. Nori is considered one of the safer seaweeds for regular consumption compared to hijiki (arsenic concern) or kelp varieties (which can easily exceed safe intake limits if consumed in quantities larger than a snack). For iodine reliability, nori is a reasonable occasional choice rather than a daily staple.

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. For these reasons, seaweed is best used deliberately and in moderation — for example, 1–2 nori sheets several times per week, or small amounts of wakame in miso soup — rather than as an unlimited daily staple. If you seek reliable iodine, iodized salt or a plant-based supplement provides more consistent intake. Monitor your thyroid function with TSH testing if consuming seaweed regularly.

Iodine is literally built into thyroid hormones — each T4 (thyroxine) molecule contains four iodine atoms, and T3 contains three. The thyroid gland cannot synthesize thyroid hormones without adequate iodine. Iodine is also required for thyroid peroxidase, the enzyme that incorporates iodine into the hormone molecules. Without sufficient iodine, the thyroid is unable to produce adequate hormone, leading to hypothyroidism and goiter. For comprehensive thyroid support on a plant-based diet, combine adequate iodine (via iodized salt, seaweed, or supplements) with adequate selenium (from sunflower seeds, wheat germ, oats, chia seeds, and legumes) — selenium is required for thyroid hormone conversion and for selenoproteins that protect thyroid tissue from oxidative damage.

Yes — excessive iodine intake can trigger hypothyroidism, especially in individuals with pre-existing autoimmune thyroiditis or Hashimoto's disease. The Tolerable Upper Intake Level (UL) is 1,100 µg per day for adults. To contextualize: one sheet of nori (~3g) provides ~110 µg (safe); one teaspoon of iodized salt provides ~450 µg (safe in typical amounts); but just 1 gram of dried kelp can provide 15,000 µg — far exceeding safe limits. This is why kelp supplements and heavy daily seaweed consumption require careful monitoring and medical supervision. For plant-based eaters, the safest approach is either moderate iodized salt use or a 150 µg plant-based supplement. If consuming seaweed regularly, ask your healthcare provider to monitor your TSH (thyroid-stimulating hormone) level annually.

Iodine and selenium work synergistically to support optimal thyroid health. Iodine is the structural component of T3 and T4 thyroid hormones, while selenium is required for three critical enzymes: (1) thioredoxin reductase, which converts T4 (inactive form) to T3 (active form); (2) glutathione peroxidase, which protects thyroid tissue from oxidative damage; and (3) other selenoproteins involved in thyroid function. Without adequate selenium, even with sufficient iodine, thyroid hormone activation and thyroid protection are impaired. Plant-based sources of selenium include sunflower seeds (~77 µg per ounce), wheat germ, oats, chia seeds (~55 µg per ounce), and legumes. For optimal thyroid support on a plant-based diet, ensure both nutrients: iodine via iodized salt or supplements, and selenium via seeds and whole grains.

Plant-based iodine supplements are a safe, reliable, and recommended option for plant-based eaters who prefer not to use iodized salt or seaweed. Common supplement forms include potassium iodide and seaweed-derived iodine extracts. A standard supplement dose is 150 µg per day, matching the RDA for non-pregnant adults. Supplements eliminate guesswork and the variability and contamination risks associated with whole seaweed products. Many plant-based nutrition experts recommend supplementing 150 µg iodine daily if not using iodized salt and not regularly consuming seaweed. This is especially important for pregnant and lactating individuals, who need 220–290 µg daily. Iodine supplements are inexpensive, shelf-stable, widely available, and remove the need to monitor and limit seaweed intake to avoid excessive dosing.

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. Seaweed iodine is also relatively heat-stable during typical cooking (simmering in broth, gentle steaming, toasting). The key practical point: if you rely on iodized salt for iodine, add it at the table or late in cooking rather than during high-heat preparation.

Mild iodine deficiency may present with nonspecific symptoms: fatigue, weight gain, cold intolerance, dry skin, slow heart rate, and slowed mental function — symptoms that overlap with hypothyroidism. More severe deficiency causes goiter (visible enlargement of the thyroid gland in the neck), elevated TSH, low free T4, and clinical hypothyroidism. In pregnant and lactating individuals, iodine deficiency impairs fetal and infant brain development, leading to reduced IQ, learning disabilities, delayed development, and in severe cases, cretinism (preventable intellectual disability, growth retardation, and neurological damage). Iodine deficiency is rare in developed nations due to iodized salt, but can occur in plant-based eaters who do not intentionally include iodine sources. If you experience persistent fatigue, weight gain, goiter, or depression, ask your healthcare provider to test your TSH and free T4 levels.