Is your iodine level affecting your health?

Iodine is a mineral that can be immensely underrated. It’s vital for thyroid health, but evidence suggests that many of us don’t get enough in our diets [1]. And more evidence is emerging to suggest that changes to the way food is made and the diets we choose are increasing our likelihood of developing an iodine deficiency [2]. 

Conversely, too much iodine can be harmful, affecting the thyroid, liver, and gastrointestinal tract So, how can you get it right?  

In this blog we discuss: 

• What is iodine?
• Testing for iodine
• How much iodine do I need?
• Iodine-rich foods
• Symptoms of an iodine deficiency
• Iodine deficiencies and thyroid conditions
• Are you at risk of an iodine deficiency?
• Your risk of iodine deficiency as a woman
• Your risk of iodine deficiency as a vegan
• Should I take an iodine supplement?

What is iodine?

 

Iodine is one of the most important minerals for thyroid health. The thyroid is a butterfly-shaped gland that sits in the neck and produces thyroid hormones which travel around the body and regulate every single process, from your heartbeat to your metabolism. 

Iodine is essential for thyroid health because it’s a vital component of the thyroid hormones, thyroxine (T4) and triiodothyronine (T3). Without enough iodine, our bodies cannot make these hormones, so they cannot carry out essential roles in the body. 

Recent research suggests that iodine deficiency is now a significant concern in the UK [11]. 

Testing for iodine

 

You can’t reliably check iodine levels with a standard blood test alone, which is why a thyroid blood test is often the most practical option. Because iodine is essential for thyroid hormone production, a Medichecks thyroid test can help identify whether iodine may be impacting thyroid health.

 

How much iodine do I need?

 

Adults generally need 140 mg of iodine each day to support normal thyroid hormone production. Requirements are higher during pregnancy and breastfeeding, rising to around 220 to 290 mg daily. Most people can get enough through foods such as iodised salt, dairy and seafood, and intake should generally stay below the safe upper limit of around 600 to 1,100 mg per day [3].

Iodine-rich foods

 

You can get iodine from a range of everyday foods, although some sources provide much more than others. In the UK, dairy and seafood are among the main contributors, so people who avoid these foods may need to be more mindful of their intake [4].

• Shellfish 
• Fish 
• Eggs 
• Milk and cheese 
• Iodine-fortified plant milk 
• Iodine-fortified salt 
• Seaweed 

Symptoms of an iodine deficiency

 

Symptoms of an iodine deficiency can range from very mild to very severe. Experts have put together a term to cover the whole spectrum of iodine deficiency: iodine deficiency disorders (IDD). 

A low intake of iodine means your thyroid gland must work harder, and this can produce a swelling in the neck, known as a goitre. A mild deficiency during pregnancy or in childhood, could cause a lower IQ or impact reading ability in the growing child in later life [5]. 

Symptoms of an iodine deficiency differ from person to person but may include: 

• A goitre or neck swelling 
• Cognitive problems, such as difficulty concentrating 
• Low work productivity 

Iodine deficiencies and thyroid conditions

 

As iodine is important for your thyroid health, low levels of iodine can affect how well your thyroid gland works. If you have a long-term iodine deficiency, you may develop a thyroid condition such as hyper- or hypothyroidism. Hypothyroidism is an underactive thyroid that produces too little thyroid hormone, while hyperthyroidism is an overactive thyroid that produces too much. [6].  

Symptoms of thyroid conditions include: 

• Tiredness or muscle weakness 
• Depression or other changes to your mood 
• Difficulty regulating body temperature (being too hot or too cold) 
• Abnormally slow or fast movement and thoughts 
• Changes to the menstrual cycle 
• Loss of libido (sex drive) 
• Bodyweight changes, such as weight loss or weight gain 

You can find more information on thyroid health and necessary nutrients in our Thyroid Guide.  

Are you at risk of an iodine deficiency?

 

Though iodine deficiency is reasonably rare, you can be more at risk of a deficiency if: 

• You don’t have a healthy balanced diet that includes iodine 
• You are a premenopausal or pregnant woman  
• You are a vegan  

In the past, iodine deficiency was a major problem because people relied on the food they grew to eat, and if the soil was low in iodine, the foods grown were also low in iodine. 

Food is now readily available from all over the world, so the severe form of iodine deficiency is now very rare in the UK. But there is growing concern that many people are living with milder deficiencies, which do not always have obvious symptoms. 

Many countries, such as New Zealand and the United States, have iodine fortification programmes. This means that iodine is added to some foods, such as salt and bread, to keep the population healthy. The UK does not currently have an iodine fortification programme – one of the few European countries without one. 

Your risk of iodine deficiency as a woman

 

Many teenage girls and young women in the UK may not get enough iodine in their diets [1]. 

Pregnancy and iodine

Pregnant women are at increased risk of iodine deficiency. Their needs are greater as they create more thyroid hormones and provide iodine to the baby [7]. Iodine is essential for foetal and infant neurodevelopment.

A large study found that amongst pregnant women, a mild-moderate iodine deficiency was associated with a higher prevalence of preeclampsia or pre-term labour [8].

A mild iodine deficiency during pregnancy or childhood may also affect brain development even when there are no obvious symptoms at the time. Some studies have found that mild-to moderate iodine deficiency in pregnancy is associated with lower verbal IQ and poorer reading ability in children later in life [5]. 

However, evidence on routine supplementation for pregnant women suggests that excess iodine also poses a risk to maternal and foetal health [12]. 

Women need iodine from the early pregnancy stages, so you should ensure you’re getting enough iodine in your diet for many months before getting pregnant. Check with your GP before starting any new supplements.

Your risk of iodine deficiency as a vegan

 

If you avoid dairy products (because of an allergy, intolerance, or diet), you could be at risk of iodine deficiency [9]. New research suggests that people who follow a vegan diet are at higher risk of a deficiency – so vegans should look for fortified food products.

You can read more about vegan nutrition in our blog plant-based diets and nutrition. 

Should I take an iodine supplement?

 

Like many nutrients, iodine can be harmful both in deficiency (too little) and excess (too much). Supplementation can mean you’re at a higher risk of having far too much iodine. 

Many supplements that seem harmless and natural (such as iodine-containing seaweed supplements) may be inconsistent in their iodine content. So, how can you be sure how much iodine you are putting into your body? 

The answer is that you can't be sure without measuring your levels. It’s a much safer (and cheaper) approach to increase your intake of iodine-containing foods.  

Before you consider taking iodine supplements, it’s best to discuss this with your doctor, as taking too much iodine can be harmful [10]. 

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References 

1. The Lancet Diabetes & Endocrinology (2016) “Iodine deficiency in the UK: Grabbing the low-hanging fruit,” The Lancet Diabetes & Endocrinology, 4(6), p. 469. Available at: https://doi.org/10.1016/s2213-8587(16)30055-9. 
2. Hatch-McChesney, A. and Lieberman, H.R. (2022) “Iodine and iodine deficiency: A comprehensive review of a re-emerging issue,” Nutrients, 14(17), p. 3474. Available at: https://doi.org/10.3390/nu14173474. 
3. (no date) NHS choices. NHS. Available at: https://www.nhs.uk/conditions/vitamins-and-minerals/iodine/ (Accessed:20 March 2026). 
4. Iodine (2021) The Nutrition Source. Available at: https://www.hsph.harvard.edu/nutritionsource/iodine/ (Accessed:20 March 2026). 
5. Leung, A.M. and Brent, G.A. (2013) “Children of mothers with iodine deficiency during pregnancy are more likely to have lower verbal IQ and reading scores at 8–9 years of age,” Evidence Based Nursing, 17(3), pp. 86–86. Available at: https://doi.org/10.1136/eb-2013-101585. 
6. Chung, H.R. (2014) “Iodine and thyroid function,” Annals of Pediatric Endocrinology & Metabolism, 19(1), p. 8. Available at: https://doi.org/10.6065/apem.2014.19.1.8. 
7. Pearce, E.N. (2015) “Iodine deficiency in pregnant women in the UK: The costs of inaction,” The Lancet Diabetes & Endocrinology, 3(9), pp. 671–672. Available at: https://doi.org/10.1016/s2213-8587(15)00228-4. 
8. Abel, M.H. et al. (2020) “Insufficient maternal iodine intake is associated with subfecundity, reduced foetal growth, and adverse pregnancy outcomes in the Norwegian mother, father and child cohort study,” BMC Medicine, 18(1). Available at: https://doi.org/10.1186/s12916-020-01676-w. 
9. Office for Health Improvement and Disparities (2021) Iodine: Migrant health guide, GOV.UK. GOV.UK. Available at: https://www.gov.uk/guidance/iodine-metabolism-migrant-health-guide. (Accessed:20 March 2026). 
10. (no date) NHS choices. NHS. Available at: https://www.nhs.uk/conditions/vitamins-and-minerals/iodine/ (Accessed: 20 March 2026)
11. Bath, S.C. (2026) ‘Iodine deficiency in the UK – should we take it with a pinch of salt?’, Proceedings of the Nutrition Society, First View, pp. 1–8. Available at: Cambridge Core. Accessed 20 March 2026. doi: 10.1017/S0029665125102164.
12. Committee on Toxicity of Chemicals in Food, Consumer Products and the Environment (2022) Statement on the potential effects that excess iodine intake may have during preconception, pregnancy and lactation. Available at: Committee on Toxicity. (Accessed 20 March 2026)