Iodine is one of the most overlooked nutrients on plant-based diets. The traditional sources (dairy, eggs, fish) are out. The alternatives are narrower than most people realise. Here's a UK-focused guide to why iodine matters, the actual vegan-friendly sources, and how to think about iodine supplementation without overshooting.
Key takeaways
- Iodine is essential for thyroid function and metabolic regulation. UK reference intake is 150 mcg/day for adults.
- Plant-based diets often run low on iodine. Vegan and dairy-free eaters frequently fall below the 150 mcg threshold without specific intake.
- Sea vegetables (sea moss, kelp, nori, dulse) are the strongest plant sources, but iodine content varies dramatically between species and harvest.
- Iodised salt is widely used internationally but not standard in UK kitchens. UK table salt is usually not iodised.
- The upper safe limit matters too. EFSA tolerable upper intake is 600 mcg/day; consistently very high iodine (over 1,100 mcg/day) can disrupt thyroid function.
Why iodine matters
Iodine is a trace mineral that the thyroid gland uses to produce T3 and T4 thyroid hormones. These hormones regulate:
- Basal metabolic rate
- Body temperature regulation
- Energy metabolism
- Neurological development (especially critical during pregnancy)
- Normal cognitive function
Adequate iodine intake supports normal thyroid function. Inadequate intake over time can contribute to goitre (thyroid enlargement), hypothyroidism, and during pregnancy, can affect foetal neurological development.
The UK is officially classified as a "mildly iodine-deficient" country by some international bodies, with surveys suggesting many UK women of childbearing age fall below the recommended intake.
Why vegans often run low
The dominant iodine sources in typical UK diets are:
- Dairy products: cows are often fed iodine-supplemented feed, and cleaning agents in dairy facilities contribute too. A 200 ml glass of milk provides ~50 to 100 mcg iodine.
- Eggs: chickens fed iodine-supplemented feed lay eggs with meaningful iodine content. ~25 mcg per egg.
- White fish, prawns, shellfish: ~70 to 100 mcg per 100g serving.
- Iodised salt: in countries where it's standard. Less so in UK.
Cut out dairy, eggs and fish, and you've eliminated the four biggest dietary iodine sources at once. Without conscious replacement, intake can drop below 50 mcg/day, well under the 150 mcg target.
The vegan iodine sources that actually deliver
1. Sea vegetables (the only major plant source)
Marine algae are by far the most concentrated plant-based iodine source. Common varieties:
- Kelp/kombu: extremely high iodine, often 1,000 to 3,000+ mcg per gram dried. So concentrated that small amounts can easily exceed safe upper limits.
- Wakame: ~40 to 60 mcg per gram dried.
- Nori: lower than kelp, ~16 to 43 mcg per gram dried. The seaweed in sushi rolls.
- Dulse: variable, ~30 to 60 mcg per gram dried.
- Irish Sea Moss: variable, ~50 to 150 mcg per gram dried.
The challenge: sea vegetable iodine content varies enormously between species, harvest location, and even between batches. This is why bulk kelp powder isn't a reliable iodine strategy, you can easily double or triple your safe upper intake without realising.
2. Iodised salt
Common internationally but inconsistently sold in UK supermarkets. Look specifically for "iodised salt" or "iodine-fortified salt" on the label. Standard UK sea salt and table salt are usually NOT iodised.
3. Iodine-fortified plant milks
Some UK plant milk brands fortify with iodine to roughly match cow's milk content. Check the label specifically, fortification varies brand to brand, and not all plant milks include iodine.
4. Specific iodine supplements (potassium iodide)
Standalone iodine supplements typically deliver 150 mcg per dose, matching the UK reference intake. Useful as a clean, predictable source for vegans whose dietary intake is inconsistent.
How sea moss compares as an iodine source
Wildcrafted Atlantic Irish Sea Moss (Chondrus crispus) typically contains 50 to 150 mcg of iodine per gram of dried algae. Compared to kelp, sea moss is more moderate in iodine concentration, which is actually a feature, not a bug, because it makes safe daily dosing more predictable.
Our Healthier Options Sea Moss Gummies use 1,600 mg of Wildcrafted Irish Sea Moss per 2-gummy serving, dosed within UK iodine safety guidance per serving. The traditional three-botanical stack pairs sea moss with bladderwrack and burdock root for a more complete mineral profile. Read more in our deep-dive on the three-botanical stack.
The dose that's safe and useful
UK guidelines:
- 150 mcg/day: reference intake for adults
- 200 to 250 mcg/day: increased reference intake for pregnancy and breastfeeding
- 600 mcg/day: EFSA upper tolerable intake (the level beyond which thyroid disruption risk increases)
- 1,100 mcg/day: US National Academy upper limit; consistently above this can disrupt thyroid function
The window between "useful" and "too much" is narrower with iodine than with most nutrients. This is why predictable, dosed sources (sea moss gummies, fortified milks, iodine supplements) are usually safer for vegans than ad-hoc kelp powder.
Iodine for specific groups
Pregnancy and breastfeeding
Iodine requirements increase during pregnancy. The British Dietetic Association specifically recommends iodine attention for women planning pregnancy or pregnant on plant-based diets. Discuss iodine supplementation with your GP or midwife.
Thyroid conditions
If you have hyperthyroidism, hypothyroidism, Hashimoto's, Graves', or take levothyroxine, do NOT start iodine supplements without consulting your endocrinologist or GP. Iodine intake interacts directly with thyroid function and your treatment.
Children
Children's iodine needs are lower than adults' but still essential. Use specific paediatric formulations or speak to a paediatric dietitian.
How to check your iodine status
If you're concerned about iodine intake, two options:
- Track diet for 1 to 2 weeks and estimate intake using nutrition databases. If you're consistently under 150 mcg/day, supplementation is reasonable.
- Urinary iodine test (UIC): GPs can order this; it measures actual iodine excretion (a reasonable proxy for intake). NHS availability varies; private testing is widely available.
Don't take megadoses of iodine to "be safe." More is not better; the safety window is narrower than for most vitamins.
Common questions
Will iodine help with energy levels?
If you're genuinely deficient, restoring iodine intake can support thyroid function and indirectly energy/metabolism. If you're already iodine-sufficient, more iodine won't add energy.
Can vegans get enough iodine without sea moss or kelp?
Yes, with care. Iodine-fortified plant milks, iodised salt (where available), and a 150 mcg potassium iodide supplement can cover requirements. But sea vegetables remain the strongest natural plant source.
Is sea moss a "complete" iodine source?
It's a contributor, not a complete strategy. The variable iodine content per gram of sea moss makes it hard to dose with precision. Quality sea moss gummies that quote iodine per serving are more predictable than raw powder.
How much sea moss is too much?
For most quality sea moss gummies, 2 gummies a day delivers iodine within UK safety guidance. 4+ gummies a day stacks iodine intake significantly and approaches upper safe limits, especially combined with other dietary sources. Our 2-gummy daily serving is dosed for the safety window. Read more in our sea moss dosage guide.
References
- NHS UK. "Iodine: vitamins and minerals." Available at: nhs.uk/conditions/vitamins-and-minerals/iodine.
- British Dietetic Association. "Iodine: Food Fact Sheet." 2023.
- EFSA. "Tolerable Upper Intake Level of Iodine." 2014.
- Bath SC et al. "A multi-centre pilot study of iodine status in UK schoolchildren." Br J Nutr. 2016. PubMed: 27267128.
Food supplements are not intended to treat, cure or prevent any disease. If you are pregnant, breastfeeding, taking medication, or have a medical condition, consult a healthcare professional before use.
