What is iodine and why do I need it?
Iodine helps regulate your metabolism and is essential for a healthy pregnancy. But research shows many women don’t get enough. So how much do you need, and where can you find it?
By Laura Tilt, dietitian
Iodine is an essential mineral which we need in small amounts to produce thyroid hormones.
The human body contains around 15-20 milligrams of iodine and most of this is stored in the thyroid gland, a butterfly shaped organ in your neck.
Why do we need iodine?
Iodine is used by your thyroid gland to make two thyroid hormones: T4 (thyroxine) and T3 (triiodothyronine). Thyroid hormones regulate your metabolic rate, or the speed at which the chemical processes in your body take place – like the process of turning food into energy.
Iodine is particularly important during pregnancy and early life, as the development of a baby’s brain and nervous system is driven by thyroid hormones. Severe iodine deficiency during pregnancy can lead to irreversible brain damage, but even mild deficiency has been linked with impairments in cognition and school performance in childhood.
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How much iodine do I need?
In the UK, the recommended daily intake of iodine is 140 micrograms, with no pregnancy-specific guidelines. But this is thought to be outdated.
Other health organisations encourage a higher intake during pregnancy. The World Health Organisation recommends 250 micrograms per day, and European guidelines sit at 200 micrograms per day.
Research has found that awareness of iodine’s importance in pregnancy is low in women, and few mothers or mums-to-be feel confident about how to increase their intake.
In fact, girls aged 11 to 18 years and women of childbearing age (16 to 49 years) are less likely than other groups to have enough iodine.
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Which foods are high in iodine?
The answer to this isn’t as straightforward as you might think. That’s because the iodine content in food varies according to how much iodine is in the soil or water that it grows in.
Over time, ice, snow and rain have rinsed much of the iodine from the earth’s surface soil into the sea. Because of this, many countries have iodine-deficient soils, meaning the crops grown in them are also low in iodine.
Since the 1920s, many countries (including the US and Canada) have added iodine to salt as a cheap and effective method of treating and preventing iodine deficiency, but the UK hasn’t adopted this approach.
In the UK, milk and dairy foods contribute about 40% of our total iodine intake. Cow’s milk isn’t naturally rich in iodine, but changes in farming practices mean iodine has been added to animal feed since the 1930s, and iodine-based sterilisers are used in milking.
Given that iodine leached from soil ends up in the ocean, fish and shellfish are other good sources. Still, fish doesn’t count hugely towards iodine intake in UK adults, because most people eat less than one portion a week.
| Food | Serving size | Iodine content | Recipe idea |
|---|---|---|---|
| Cod, baked | 100g (medium fillet) | 160 micrograms | Harissa baked fish with bulgur wheat |
| Crab | 100g (small pot, cooked) | 218 micrograms | Crab curry |
| Mussels | 100g mussels with shells (about 7-8) | 247 micrograms | Mussels puttanesca |
| Egg, boiled | 2 medium sized | 57 micrograms | Egg muffins |
| Semi-skimmed milk* | 250ml glass | 65 micrograms | Hot chocolate |
| Yoghurt | 125g pot | 45-78 micrograms | Strawberry lassi |
| Fortified soy milk | 250ml glass | 56 micrograms | Healthy berry banana smoothie |
* There are slight differences in iodine content between skimmed, semi and full-fat milk and whether the milk’s produced in winter or summer.
What happens if I don’t get enough iodine?
Over time, a lack of iodine can lead to hypothyroidism (or an ‘underactive thyroid’) where the thyroid gland can’t make enough thyroid hormones. Symptoms of hypothyroidism include tiredness, dry skin, constipation and feeling sensitive to the cold.
When iodine intake is low, the pituitary gland (a small, pea-sized gland in your brain) increases thyroid stimulating hormone in an attempt to increase iodine uptake. This sends a message to the thyroid gland to try and ‘trap’ more iodine from the circulation, which causes the thyroid gland to swell and become bigger.
The enlarged thyroid gland is known as a ‘goitre’ and is seen as a lump, usually at the front of the neck.
Many paintings from the Renaissance period show people with swollen necks because iodine deficiency was endemic in many countries at that time.
In the UK, goitre was widespread in the 1800s and early 1900s. But the addition of iodine to cattle feed in the 1930s, along with post-war campaigns encouraging people to drink milk, helped eradicate goitre by the ’60s.
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Should I be worried about iodine deficiency?
Severe iodine deficiency is rare in the UK these days, and data from the NDNS (The National Diet and Nutrition Survey) show that, overall, the iodine status of UK adults isn’t bad.
But recent studies have found mild to moderate iodine deficiency in schoolgirls, women of child-bearing age and pregnant women in various parts of the UK. This is a concern because having a good iodine status is important for anyone planning to conceive.
Because there’s no iodine fortification programme in the UK, iodine intakes depend on our personal food choices. Based on what the research shows and the lack of iodine in plant foods, people more at risk of deficiency include:
- Women who are pregnant, planning to be pregnant or breastfeeding
- People eating a plant-based diet
- People who don’t eat much dairy or fish
How can I meet the recommended intake?
Milk, eggs and fish are all positively linked with iodine status, so if you eat these regularly, you should be able to get enough iodine. You could meet the recommended adult intake with a medium latte and small pot of yogurt, or eating a fish-based dinner like these cod and crab cakes.
If you are planning a pregnancy or are already pregnant, including a pregnancy multivitamin can help you meet the increased requirement consistently.
If you eat a plant-based diet, you’ll need to supplement or choose a plant milk with added iodine, ideally 25 micrograms of iodine per litre.
At this level, including 500ml a day (half a standard carton) will provide almost 90% of the recommended daily intake. So that could be achieved with a cup of plant milk in porridge and another cup in a latte, protein shake, smoothie or hot chocolate.
What about supplements?
If you’re following a plant-based diet, are pregnant or planning a pregnancy, a supplement can help make sure you meet the higher requirements. Most pregnancy multivitamins will contain between 140 and 200 micrograms, but check the label to find out.
If you are thinking about a supplement, avoid ones made from seaweed as they can contain excessive levels which can be problematic. The NHS states that taking up to 500 micrograms is unlikely to cause any harm, though.
All content within this article is provided for general information only, and should not be treated as a substitute for the medical advice of your doctor or any other health care professional. Always consult your GP if you’re concerned about your health.
Laura Tilt is a registered dietitian with a master’s in public health nutrition and a postgraduate diploma in dietetics. Since qualifying in 2012, she has specialised in gastroenterology at London’s UCLH before moving into freelance practice. With over 10 years of experience translating nutrition science into accessible, meaningful advice, Laura’s specialist interests include digestive health, disordered eating, and sports nutrition.
Originally published August 2025
