Nobody warns you about iodine. In an omnivore’s week it arrives by accident, in milk, yoghurt, eggs and white fish, because dairy farms disinfect udders with iodine and cows eat iodised feed. Take all of that out and nothing replaces it. Iodine does not live in vegetables in any dependable amount; soil levels vary a hundredfold, and inland soil, including most of Sweden, is poor. The thyroid uses it to make the hormone that sets your metabolic rate, which is why the symptoms of low iodine feel like someone turned the whole system down a notch.
The signs iodine is low
- Cold all the time, and a body temperature that runs low in the morning.
- Slow, heavy, foggy mornings; weight that creeps up on the same food.
- Dry skin, thinning outer eyebrows, a voice that sits lower or sounds hoarse.
- Constipation; puffiness around the face and eyes.
- In the mirror, a fullness at the base of the neck: the thyroid enlarging to catch more iodine.
Low iodine and low iron overlap and often arrive together on plants; each makes the other worse because the thyroid needs iron to use iodine.
The tests, and what the numbers mean
| Test | What it tells you |
|---|---|
| TSH | rises when the thyroid is struggling; above 4 mIU/L with symptoms is worth acting on, 1 to 2.5 is comfortable |
| Free T4 | the hormone itself; low-normal with a high TSH is the iodine pattern |
| Urinary iodine (spot) | below 100 µg/L suggests low intake, but it swings day to day; use it as a population tool, not a verdict |
| Thyroid antibodies (TPO) | if raised, iodine must be dosed carefully, at the reference amount and not above |
If TSH is high and antibodies are negative in a vegan who uses no iodised salt and no fortified milk, iodine is the first thing to fix, and the response can be fast.
How much you need
| Reference | Amount |
|---|---|
| Adults, EFSA and WHO | 150 µg a day |
| Pregnancy | 200 µg a day (EFSA); 220 to 250 µg (US and WHO) |
| Breastfeeding | 200 to 290 µg a day |
| Tolerable upper intake | 600 µg a day (EFSA); 1,100 µg (US) |
Iodine has a narrow window: too little slows the thyroid, and a large excess, which kelp can deliver in a single spoon, can also switch it off or tip an autoimmune thyroid over. The answer is a steady, measured amount every day, not an occasional seaweed feast.
Vegan iodine sources, per serving
| Source | Serving | Iodine |
|---|---|---|
| Iodised table salt (Swedish and most EU salt, 50 µg per g) | 1 g, about a fifth of a teaspoon | 50 µg |
| Iodised salt | 3 g, the amount a normal day’s cooking uses | 150 µg |
| Iodine-fortified oat or soy milk | 250 ml | 40 to 70 µg where fortified; many are not, read the label |
| Nori | 1 sheet (about 3 g) | 16 to 43 µg |
| Wakame, dried | 2 g | about 80 to 150 µg, variable |
| Kelp, kombu | 1 g | can exceed 1,000 µg; one serving can pass the upper limit |
| Potatoes with skin, beans, cranberries | normal portions | 5 to 15 µg, soil-dependent, do not rely on them |
| Sea salt, Himalayan salt, flaky salt | any | essentially none unless the label says iodised |
The practical rule: cook with iodised salt, and treat seaweed as a flavour, not as a supplement. Nori a few times a week is fine. Kelp is for soup stock you strain off, not for daily spoons.
The supplement
If you do not salt your food, eat low-salt for blood pressure reasons, are pregnant or planning to be, or your TSH is already raised, take it as a supplement rather than hoping the salt covers it.
- Form: potassium iodide or potassium iodate; both work. Many vegan multivitamins carry 150 µg, which is the right amount; check it is there, as some leave it out.
- Dose: 150 µg a day; 200 µg in pregnancy and while breastfeeding, started before conception if you can.
- Not: kelp tablets, which are unstandardised and routinely exceed the upper limit.
- With raised thyroid antibodies, stay at 150 µg and let a clinician watch TSH; do not go higher.
Retest TSH and free T4 after eight to twelve weeks.
The one-week fix
- Replace the salt in the kitchen with iodised salt. Keep the flaky salt for the table if you love it; the cooking salt is where the daily dose comes from.
- Check the milk carton. If it is not fortified with iodine, switch brands or add the supplement.
- If you are pregnant, planning, or have been feeling cold and slow for months, start 150 µg today and book TSH and free T4 for the week after next.
- Put the kelp away.
What the research says
- Eveleigh and colleagues, Nutrients, 2020, systematic review of 15 studies, adult vegans, vegetarians and omnivores on their habitual diets: vegans had the lowest iodine intakes, and most of the included papers reported intakes below recommendations in vegans. The contrary finding: where iodised salt or a supplement was used, intakes were adequate, and seaweed users sometimes exceeded the safe upper amount. doi.org/10.3390/nu12061606
Both ends of that finding are the lesson: the gap is real and the overshoot is real. Measured and daily beats both.
Questions women ask
Can I get iodine from sea salt? No. Sea salt loses nearly all of its iodine in processing. Only salt labelled iodised carries a useful amount.
Is seaweed enough on its own? Not reliably. Nori is too low to carry the day and kelp is too high to use daily. Iodised salt or a 150 µg supplement is the dependable route.
I feel cold and tired but my TSH is normal. What now? Check ferritin and vitamin D next; low iron produces the same cold, and the three often travel together on a plant-based plate.