Iodine is an essential trace mineral that the thyroid gland uses to make thyroid hormones. These hormones help regulate metabolism, body temperature, growth, brain development, and many other important body functions. In many countries, iodine comes primarily from iodized salt, dairy products, and seafood. Vegans can obtain iodine from iodized salt and certain types of seaweed, consumed in appropriate amounts.
Symptoms of low iodine can be subtle at first, fatigue, feeling cold, dry skin, or thinning hair, but long-term deficiency can lead to a goiter (an enlarged thyroid) or hypothyroidism.
The Daily Target
Unlike calcium, which we need in large amounts, we only need a tiny “trace” of iodine daily. However, the window for “just right” is smaller, as too much iodine can also cause thyroid issues.
| Life Stage | US Recommended (RDA) | UK Recommended (RNI) |
|---|---|---|
| Adults (19+) | 150 mcg | 140 mcg |
| Pregnancy | 220 mcg | 140 mcg* |
| Lactating | 290 mcg | 140 mcg* |
Note: mcg stands for micrograms. 1,000 mcg=1 mg.
- Adult (19+)UK Dietary Reference Values do not include an extra increment for pregnant or lactating women
Plant-Based Sources of Iodine
One whole-food sources of iodine are sea vegetables. Because iodine levels in seaweed vary wildly based on the water they grew in, it’s helpful to know which ones are “powerhouses” and which are “gentle.”
This table highlights the significant variation in iodine content across plant-based sources. For those following a whole-food approach, rotating these options ensures consistent intake without exceeding the daily recommended limit.
| Food Source | Serving Size | Weight (g) | Iodine* (mcg) | Notes |
|---|---|---|---|---|
| Kombu (Kelp) | 1 small strip | ~1g | 2,000+ mcg | Extremely high. Best used to flavor broths or beans and then removed. |
| Dulse | 1 tbsp (flakes) | ~3g | 150–200 mcg | Highly reliable. A single tablespoon typically meets 100% of the RDA. |
| Wakame (Miyeok) | 1g (dried) | ~1g | 66 mcg | Great in soups. |
| Iodized Salt | 1/4 tsp | ~1.5g | 78 mcg | |
| Nori Sheets | 1 sheet | ~2g | 30–40 mcg | The “sushi” seaweed. A safe and moderate option for regular snacking. |
*Note: The iodine content of seaweed can vary dramatically depending on the species, harvest location, season, and processing. Values shown are approximate averages and should not be considered exact. Kombu (kelp) is particularly variable and may contain several thousand micrograms of iodine per gram.
Incorporating Seaweed: The Whole-Food Approach
Seaweed is a highly concentrated source of natural iodine, meaning a small amount goes a long way. To maintain balanced levels, rotate through these options throughout the week rather than consuming them all at once.
- Nori: Eating 2–3 sheets of nori provides approximately half of the daily iodine requirement.
- Wakame: It can be served a few times a week in dishes like Korean seaweed soup (Miyeok-guk) or Miso soup.
- Kombu for Beans & Pulses:Â Adding a small strip of Kombu now and then to the water when boiling beans or pulses helps soften the texture and improves digestibility. The strip can be removed and discarded after boiling, as the iodine will have infused the pot.
- Dulse: Dulse flakes can be used as a seasoning, sprinkled over savory soups or even added to homemade vegan desserts for a subtle, salty contrast.
- Goitrogens:Â If you regularly eat large amounts of raw cruciferous vegetables (such as broccoli, kale, and bok choy), getting enough iodine is especially important. These vegetables contain compounds that can reduce iodine uptake by the thyroid, but for most people with adequate iodine intake, they do not adversely affect thyroid function. Cooking further reduces this effect.
The Seaweed Balance
While seaweed is a nutritional powerhouse, it can also be extremely rich in iodine. Depending on the species, even a small serving may provide several times the recommended daily intake, and some varieties, especially kombu (kelp), can exceed the adult Upper Intake Level of 1,100 mcg in a single gram. To support healthy thyroid function, choose just one iodine-rich source per day and treat seaweed as a flavorful sprinkle or garnish rather than a meal base.
