Iodine tablets and food sources in the UK

What are iodine tablets?

"Iodine tablets" can mean two different things. One is a food supplement, taken daily in a small dose measured in micrograms (µg). The other is potassium iodide, a medicine for a nuclear emergency, which is not a supplement and not for everyday use.

Potassium iodide tablets and nuclear emergencies

Potassium iodide tablets are issued only if the government or emergency services advise it, after an incident at a nuclear reactor that could release radioactive iodine. GOV.UK says they work by stopping the thyroid absorbing radioactive iodine, and that they protect only the thyroid, not the rest of the body from other kinds of radiation. A UK Health Security Agency protocol describes a 65 mg tablet, equivalent to 50 mg of iodine. The NHS figure for adults is 140 µg a day, and 50 mg is 50,000 µg.

GOV.UK says to take only the tablets provided for this purpose, at the time you are told. A first dose taken more than 24 hours after exposure can cause more harm than benefit. It also warns that iodised salt is no substitute, because it won't give the protection and may be dangerous, and a supplement from a shop isn't a stand-in either.

Is iodine banned in the UK?

No. Iodine is an essential nutrient, the NHS gives an amount adults need and a supplement level it considers unlikely to cause harm, and iodine supplements are on sale. People who ask this are probably thinking of one of three things.

• Lugol's iodine is a strong iodine solution that one NHS formulary lists as an unlicensed medicine restricted to hospital (secondary care) use. It is a specialist medicine and not a supplement.
• Iodine tincture, the antiseptic, can be hard to find. Asked in 2024 whether it knew that no iodine antiseptic was available in high street pharmacies, the MHRA replied that iodine tincture held a general sale licence, with an exemption from the "sunset clause" (which cancels a licence for a medicine not sold for three years) running to 3 October 2024. That points to a supply problem.
• Iodised salt isn't standard because the UK has never required salt to be iodised. More on that below.

We found no UK law or MHRA notice banning iodine as a nutrient.

How much iodine do you need per day?

The NHS says adults need 140 µg of iodine a day and that most people can get it from a varied, balanced diet. Other bodies quote slightly different figures.

At the top end, the NHS says 0.5 mg (500 µg) or less a day from supplements is unlikely to cause harm, and that taking high doses for long periods could change the way your thyroid works. The BDA gives a rough guide that adult intake from all sources shouldn't exceed 600 µg a day, adding that the safe amount varies between people. Labels use either unit, so check: 0.5 mg and 500 µg are the same amount.

Which foods are rich in iodine?

Fish, milk and dairy products are the richest sources, according to the BDA, with white fish containing more than oily fish. The NHS also lists eggs and shellfish. The table gives the BDA's average iodine per portion, though real values vary with the season, the soil, farming practice and the type of fish.

Plant foods contribute little. The NHS says iodine in cereals and grains depends on the soil they were grown in.

Seaweed and kelp

Seaweed is very high in iodine, but it varies too much to be a dependable source. A BDA guide for dietitians puts 5 g of nori or kelp anywhere from 50 to 3,800 µg. The BDA advises against eating brown seaweed or kelp more than once a week, especially in pregnancy, and the Committee on Toxicity (COT) found that high consumers of seaweed may reach iodine levels that could pose a risk to maternal health.

Does sea salt have iodine?

Not in useful amounts. The Scientific Advisory Committee on Nutrition (SACN) says the iodine in sea water is lost when it evaporates to make salt, so sea salt and mined salt are not significant sources. A 2014 UK paper called the idea that sea salt is a good iodine source a common myth.

The UK has never made salt iodisation mandatory, and iodised salt took less than 1% of the table salt market in that paper. A shelf survey found it in 32 of 77 supermarkets. The BDA now says it is available in some branches of several supermarket chains, but also that official advice is to eat less salt, so iodised salt shouldn't be relied on to raise iodine intake.

Milk, plant drinks and iodine in the UK

With no fortification programme, UK iodine intake depends on food choices. In the national diet survey data reviewed by SACN in 2014, milk and dairy foods provided about a third (33%) of adult iodine intake. The amount in milk changes with the season, and SACN reported organic milk as 42% lower in iodine than conventional.

Unfortified plant drinks contain very little iodine. A study of 47 UK products bought in 2015 found the 44 unfortified drinks had a median iodine concentration of 1.7% of that in winter cows' milk, and only three of the 47 were fortified. In national diet survey data from 2014 to 2017, people who drank only milk alternatives had a lower iodine intake than cows' milk drinkers, 94 against 129 µg a day. Some brands have since started fortifying, so check the label.

Iodine in pregnancy and breastfeeding

The UK reference intake doesn't rise in pregnancy, and SACN's 2014 review found insufficient evidence to change that. The BDA, using EFSA figures, gives 200 µg for pregnancy and breastfeeding and says low intake in pregnancy may affect a baby's brain development, so it advises reaching the adult amount before pregnancy.

Excess carries risk too: COT concluded that too much iodine in pregnancy may affect maternal and fetal thyroid function. The BDA says there is no official UK recommendation to take an iodine supplement. It adds that many, but not all, pregnancy multivitamins contain iodine, and that any supplement shouldn't provide more than 150 µg, with the rest coming from food. Kelp supplements are best avoided, and your midwife, GP or pharmacist can advise before you start anything.

Choosing an iodine supplement in the UK

The BDA says it is better to meet iodine needs through food where possible, and that a supplement may be useful if you eat little iodine-rich food. The NHS says someone on a strict vegan diet, with no fish, eggs, cows' milk or dairy, may want fortified foods or a supplement, and to seek advice first. Vegans may also want to check vitamin B12. If you do choose a tablet:

• Look at the form. The BDA says iodine in supplements should be potassium iodide or potassium iodate, not kelp or seaweed, because the iodine in those can differ greatly from the label.
• Look at the amount per tablet in µg. The BDA says a supplement shouldn't exceed the 150 µg adult requirement, and the NHS says 0.5 mg or less a day is unlikely to cause harm.
• Add up every product. Multivitamins can contain iodine too, so total the labels.

If you have a thyroid condition or take thyroid medicine

The BDA says people with thyroid disease, or with low iodine intake over many years, should check with a GP before taking extra iodine, because an amount that is normal for most people may affect them. The NHS says the main cause of an underactive thyroid in the UK is an autoimmune condition, Hashimoto's disease, and that not getting enough iodine is a rare cause. Tiredness, feeling cold or hair loss can have many causes, so see a GP rather than trying iodine. The NHS also asks anyone starting levothyroxine to tell their doctor about any vitamins or supplements they take, and our guide to supplements to take together covers spacing around it.

Where Natura fits

Natura's Daily Iodine (coming soon) is one tablet giving 140 µg of iodine as potassium iodide, and its label says "Not thyroid hormone". Iodine contributes to the normal production of thyroid hormones and normal thyroid function, and to normal cognitive function. You'll find it among the single bottles. Iodine also appears in Daily Multi (150 µg) and the Trace Pack, and Daily Thyroid in the Thyroid Pack gives 60 µg. Add the totals if you combine products: Daily Iodine with Daily Multi comes to 290 µg a day, under the NHS 0.5 mg but above the BDA's 150 µg guide for a supplement.