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Hypothyroidism and Diet: The Key Role of Iodine and Seaweed

Hypothyroidism and Diet: The Key Role of Iodine and Seaweed

- Categories : Algae Rss feed , Feminine Rss feed , Wellbeing advices Rss feed

Summary

At Biovie, we have been supporting health-conscious individuals for years, and the topic of the thyroid frequently comes up in our discussions, especially when it comes to seaweed. Honestly, when we delve into the subject, we realize how crucial a role diet plays in the proper functioning of this small butterfly-shaped gland located at the base of our neck.

Iodine is truly the fuel for your thyroid. Without it, she cannot produce the T3 and T4 hormones that help regulate your metabolism, energy, and body temperature. In cases of hypothyroidism, adjusting one's diet can help support normal thyroid function and contribute to improved daily well-being. Specifically, I will explain how iodine works, what the best dietary sources are, and why seaweed is a particularly interesting natural solution—provided you know how to use it correctly.

Important : A varied and balanced diet and a healthy lifestyle are important. The information presented here does not replace medical advice. In case of diagnosed hypothyroidism or hyperthyroidism, always consult your doctor.

Understanding the link between iodine and the thyroid

Why iodine is essential for your thyroid

Your thyroid functions like a small hormone production factory. To produce its hormones, it needs one absolutely essential ingredient: iodine. It's as simple as that. Without iodine, hormone production is not possible.

Here's how it works: your thyroid absorbs the iodine present in your blood and uses it to synthesize two main hormones, T4 (thyroxine) and T3 (triiodothyronine). These hormones are then released into your body where they play a role in regulating your metabolism, body temperature, heart rate, and even your mood (Zimmermann & Boelaert, 2015).

A systematic review published in The Lancet Diabetes & Endocrinology confirmed that iodine is the most important micronutrient for thyroid function, and that even a moderate deficiency can lead to impaired hormone production (Zimmermann & Boelaert, 2015). What the researchers have demonstrated is that the body cannot produce iodine on its own. It must absolutely obtain it from the diet.

For my part, I like to use the analogy of the engine: imagine your thyroid as the engine of your car, and iodine as the fuel. You can have the best engine in the world, but if you don't put fuel in it, it simply won't start.

How much iodine do you need per day ?

Iodine needs vary according to your profile. The World Health Organization (WHO) and ANSES (French Agency for Food, Environmental and Occupational Health & Safety) have established specific recommendations (WHO, 2007):

  • Adults : 150 µg per day
  • Pregnant women : 200 to 250 µg per day
  • Breastfeeding women : 200 to 250 µg per day
  • Children aged 1 to 8 years : 90 µg per day
  • Adolescents : 120 to 150 µg per day

The EFSA (European Food Safety Authority) has also set an upper safety limit of 600 µg per day for adults (EFSA, 2014). Beyond this, one enters a zone where excess iodine can paradoxically disrupt thyroid function. This is the paradox of this trace element: too little is problematic, and too much is as well.

Alert 2024: Iodine deficiency reappears in France

Here is some information that truly caught my attention. The WHO sounded the alarm in 2024: iodine deficiency, which was thought to be under control in developed countries, is making a comeback in Europe, including in France (Zimmermann & Andersson, 2021). Certainly, cretinism has been eradicated, but deficiencies are resurfacing.

A study from the Erasme Hospital in Brussels, published in theEuropean Journal of Nutrition, revealed that Nearly 30% of women of childbearing age have an iodine deficiency. in several European countries (Vandevijvere et al., 2012). The reasons are multiple: a decrease in the consumption of seafood, ultra-processed foods (which use non-iodized salt), poorly balanced vegetarian or vegan diets.

In France, the Esteban study conducted by Santé Publique France showed that the average iodine intake remains insufficient in certain populations, particularly pregnant women (Santé Publique France, 2019). This is a real public health issue because a deficiency during pregnancy can affect the neurological development of the fetus.

Lien entre iode et thyroïde

The best dietary sources of iodine

Seaweed: Champions of Natural Iodine

Honestly, when we compare the different sources of iodine, the Seaweed are in a category of their own. No other terrestrial food can rival their content of this trace element.

Here is an overview of the average iodine content for the main types of seaweed, according to the 2018 opinion of ANSES:

  • Kombu : 1,500 to 8,000 µg per gram (dry) – to be consumed occasionally
  • Wakame : 350 to 1,500 µg per gram (dry) – ideal for regular consumption
  • Dulse : 80 to 150 µg per gram (dry) – moderate content
  • Nori : 30 to 50 µg per gram (dry) – perfect for beginners
  • Sea lettuce : 25 to 40 µg per gram (dry) – very accessible

To give you a concrete idea: 1 gram of organic wakame can cover 100% of your daily iodine needs.. A single sheet of nori used for a maki represents about 30% of the recommended daily intake.

What makes seaweed particularly interesting is that the iodine it contains is naturally bioavailable. A study published in theEuropean Thyroid Journal demonstrated that iodine from seaweed is absorbed and effectively used by the body (Smyth, 2021). In addition to iodine, seaweed provides complementary minerals (calcium, magnesium, iron), vitamins, and bioactive compounds such as fucoidans.

At Biovie, we offer a full range of organic Breton seaweeds whose iodine content is controlled and displayed. The Organic wakame Biovie, For example, with its content of approximately 1,500 µg per gram, it is ideal for regular and controlled consumption.

Is iodized salt really enough ?

This is a question I am often asked. The answer is: not always.

In theory, iodized salt could meet our needs. But in practice, several factors limit its effectiveness (Leung & Braverman, 2014):

  1. Only 50% of the salt sold in France is iodized. - the other half is not
  2. Processed foods use non-iodized salt. - yet they represent a growing part of our diet
  3. Public health recommendations urge us to reduce salt. – which mechanically reduces iodine intake
  4. The iodine in salt partially evaporates during cooking. – a part is lost during preparation

A study by ANSES confirmed that relying solely on iodized salt poses a risk of deficiency, particularly for pregnant women and vegetarians (ANSES, 2012). Diversifying sources (fish, eggs, seaweed) is clearly safer.

Focus on Algae: Practical Guide for the Thyroid

Which algae to choose according to your situation ?

The choice of seaweed depends on your personal situation and your iodine needs. Here are my recommendations based on our 18 years of experience with these marine plants:

For daily consumption (moderate iodine content):

  • Organic nori : Perfect for beginners. One sheet per day for your makis or as flakes in your salads.
  • Organic sea lettuce : Very mild in taste, it easily blends into all dishes.

For regular consumption (2-3 times per week):

  • Organic wakame : It is the ultimate versatile algae. 1 gram is enough to more than meet your needs.
  • Organic dulse : Rich in iodine AND proteins, it has a characteristic slightly iodized taste.

For occasional consumption (once a week or less):

  • Organic kombu : Very rich in iodine, mainly used to flavor broths

The Biovie nori sheets are perfect for beginners. They provide about 33% of the recommended daily intake per gram, allowing for regular consumption without the risk of overdose.

Safe dosages: how much seaweed per day ?

ANSES recommends not exceeding 600 µg of iodine per day for adults (EFSA, 2014). Specifically, here is what this represents:

  • Nori : Up to 5g per day (approximately 5 leaves)
  • Sea lettuce : Up to 10g per day
  • Wakame : 1g per day (a small pinch)
  • Dulse : 2 to 3g per day
  • Kombu : 0.1 to 0.3g per day

For my part, I always advise starting slowly, with small amounts, and observing how your body reacts.

A Japanese study published in Thyroid It has also been shown that the Japanese population, which is a major consumer of seaweed, exhibits excellent overall thyroid function, provided that the intake remains within reasonable limits (Nagataki, 2008).

Precautions and contraindications

I want to be very clear on this point. Algae are extraordinary foods, but they are not suitable for everyone in all situations.

ANSES recommends a prior medical consultation for (ANSES, 2018):

  • People suffering from thyroid dysfunction (hypothyroidism or hyperthyroidism)
  • People undergoing thyroid treatment (notably Levothyrox)
  • Pregnant or breastfeeding women (as a precautionary principle)
  • People with a history of thyroid diseases

Important: If you are undergoing treatment for hypothyroidism, space the intake of seaweed by at least 3 hours from your medication. Iodine can interfere with the absorption of levothyroxine (Liwanpo & Hershman, 2009).

I repeat: nutrition never replaces medical treatment. It can accompany it, but in the case of diagnosed hypothyroidism, your doctor remains your primary point of contact.

Beyond Iodine: Other Essential Nutrients

Selenium: The indispensable partner of iodine

Iodine does not work alone. It needs a partner: selenium. This mineral contributes to the conversion of the hormone T4 (inactive) into T3 (active), which is the one that actually affects your metabolism (Schomburg, 2011).

A meta-analysis published in Thyroid demonstrated that selenium supplementation can improve certain parameters of thyroid function, particularly in individuals with autoimmune thyroiditis (Wichman et al., 2016).

The best dietary sources of selenium are:

  • Brazil nuts: 1 to 2 nuts meet daily requirements
  • Fish and seafood
  • Eggs
  • Whole grains

The recommended daily intake of selenium is 55 µg for an adult (Institute of Medicine, 2000).

Zinc, iron, and vitamins for your thyroid

Other nutrients play a complementary role in thyroid health:

Zinc: He participates in the synthesis of thyroid hormones and their action at the cellular level (Severo et al., 2019). A zinc deficiency can worsen an existing hypothyroidism. The Chlorella bio Biovie is an excellent natural source of zinc.

Iron: Iron deficiency is common in women and can affect thyroid hormone production (Hess, 2010). However, be careful: the spirulina, often cited as a source of iron, does not provide significant iodine. It remains valuable for iron and B vitamins, but does not contribute to iodine intake.

B vitamins: Notably B12, they support overall energy metabolism and are often deficient in people suffering from hypothyroidism (Jabbar et al., 2008).

The importance of the gut microbiota

This is an often overlooked aspect. Recent research published in Nutrients highlighted a link between gut microbiota health and thyroid function (Knezevic et al., 2020).

A portion of the conversion of T4 to T3 occurs at the intestinal level, under the influence of certain bacteria. An imbalanced microbiota could therefore indirectly affect thyroid function.

Concretely, this means that a diet rich in fiber, fermented foods, and low in ultra-processed foods can indirectly support your thyroid.

Foods to limit in case of hypothyroidism

Goitrogenic foods: list and precautions

Goitrogenic foods contain substances that can interfere with the absorption of iodine by the thyroid. They derive their name from the word "goiter," which is the swelling of the neck characteristic of a thyroid working overtime to compensate for a lack of iodine (Felker et al., 2016).

The list of major goitrogenic foods:

  • Cabbage (cauliflower, green cabbage, Brussels sprouts)
  • Broccoli
  • Turnip and radish
  • Cassava
  • Soy and soy products
  • Sweet potato
  • Millet

But beware – and this is important – these foods should not be completely banned. A study published in Human Toxicology showed that the goitrogenic effect is only significant in cases of excessive consumption AND pre-existing iodine deficiency (McMillan et al., 1986).

My practical recommendations:

  • Limit these foods to 1 serving per week if you have hypothyroidism.
  • Favor cooking methods that partially inactivate goitrogenic compounds.
  • Make sure your iodine intake is sufficient before worrying about goitrogens.

Soy: The Particular Case

Soy deserves a special mention. Its isoflavones can interfere with the synthesis of thyroid hormones and with the absorption of levothyroxine (Messina & Redmond, 2006).

A study of theEndocrine Practice showed that individuals undergoing thyroid treatment who regularly consumed soy required higher doses of medication (Bell & Ovalle, 2001).

Specifically, if you are undergoing treatment:

  • Space the intake of soy by at least 4 hours with your medication.
  • Limit your soy consumption to 2-3 times per week.
  • Prefer fermented products (tempeh, miso) over non-fermented ones.

Aliments à limiter en cas d'hypothyroïdie

Frequently Asked Questions

Which foods to avoid in case of hypothyroidism ?

Goitrogenic foods (cabbage, broccoli, radish, soy, sweet potato) can interfere with iodine absorption. Limit them to 1 serving per week and favor cooking, which inactivates their effects. However, if your iodine intake is sufficient, the risk remains low.

Are seaweeds good for the thyroid ?

Yes, seaweed is the most concentrated natural source of iodine, a trace element that contributes to the normal production of thyroid hormones. But be careful with your choice: nori and sea lettuce (moderate content) are suitable for regular consumption, while kombu (very rich) should be consumed occasionally. The key is in the dosage.

How much seaweed can be consumed per day ?

For an adult without thyroid problems, 1 to 3g of dried seaweed per day is safe. With wakame, 1g already covers 130% of daily needs. In case of diagnosed hypothyroidism, consult your doctor before regularly incorporating seaweed.

How to naturally increase your iodine ?

Favor sea fish (twice a week), seafood, eggs, iodized salt, and small amounts of seaweed. Soaking and cooking seaweed can reduce their iodine content by 30 to 70% if needed.

Is iodized salt sufficient for the thyroid ?

Not always. Iodized salt only accounts for 50% of the salt used in France, and processed foods use non-iodized salt. Diversifying your sources (fish, seaweed, eggs) is safer than relying solely on salt.

Can hypothyroidism be improved through diet ?

Diet does not replace medical treatment, but it can help support normal thyroid function. In cases of subclinical (mild) hypothyroidism, a diet optimized with iodine, selenium, and zinc can sometimes help stabilize markers. Always consult your doctor.

What are the symptoms of iodine deficiency ?

Chronic fatigue, sensitivity to cold, weight gain, constipation, dry skin, brittle hair, difficulty concentrating. Over time, a goiter (swelling of the neck) may appear. These symptoms are often confused with those of hypothyroidism itself.

In summary

Iodine is truly the fuel for your thyroid. In cases of hypothyroidism, adjusting your diet can help support normal thyroid function and improve your daily well-being.

Seaweeds are the most concentrated and bioavailable natural source of iodine. When used judiciously—by respecting dosages and choosing the right type of seaweed for your situation—they can be an excellent supplement to a balanced diet.

But I want to remind you: diet is a complement, not a replacement. In the case of diagnosed hypothyroidism, your doctor remains your primary point of contact. Diet is one tool among others, a valuable tool indeed, but it is part of a comprehensive approach.

Ready to support your thyroid naturally ? Discover our range of organic seaweeds, grown in Brittany, with controlled and displayed iodine levels.

Scientific bibliography

Books and institutional reports

  • ANSES (Agence nationale de sécurité sanitaire de l'alimentation, de l'environnement et du travail). (2012). Actualisation des apports nutritionnels conseillés pour les vitamines et minéraux : iode. Maisons-Alfort : ANSES. Disponible sur : https://www.anses.fr/fr/content/iode
  • ANSES. (2018). Avis relatif au risque d'excès d'apport en iode lié à la consommation d'algues dans les denrées alimentaires. Saisine n°2017-SA-0086. Maisons-Alfort : ANSES. Disponible sur : https://www.anses.fr/fr/content/avis-algues-iode
  • European Food Safety Authority (EFSA). (2014). Scientific Opinion on Dietary Reference Values for iodine. EFSA Journal, 12(5), 3660. DOI : 10.2903/j.efsa.2014.3660
  • Institute of Medicine. (2000). Dietary Reference Intakes for Vitamin C, Vitamin E, Selenium, and Carotenoids. Washington, DC : National Academies Press. DOI : 10.17226/9810
  • Santé Publique France. (2019). Étude de santé sur l'environnement, la biosurveillance, l'activité physique et la nutrition (Esteban 2014-2016). Volet Nutrition. Chapitre Iode. Saint-Maurice : Santé Publique France. Disponible sur : https://www.santepubliquefrance.fr/etudes-et-enquetes/esteban
  • World Health Organization (WHO). (2007). Assessment of iodine deficiency disorders and monitoring their elimination: a guide for programme managers (3e éd.). Genève : WHO. Disponible sur : https://www.who.int/publications/i/item/9789241595827

Peer-reviewed journal articles

  • Bell, D. S. H., & Ovalle, F. (2001). Use of soy protein supplement and resultant need for increased dose of levothyroxine. Endocrine Practice, 7(3), 193-194. DOI : 10.4158/EP.7.3.193
  • Felker, P., Bunch, R., & Leung, A. M. (2016). Concentrations of thiocyanate and goitrin in human plasma, their precursor concentrations in brassica vegetables, and associated potential risk for hypothyroidism. Nutrition Reviews, 74(4), 248-258. DOI : 10.1093/nutrit/nuv110
  • Hess, S. Y. (2010). The impact of common micronutrient deficiencies on iodine and thyroid metabolism: the evidence from human studies. Best Practice & Research Clinical Endocrinology & Metabolism, 24(1), 117-132. DOI : 10.1016/j.beem.2009.08.012
  • Jabbar, A., Yawar, A., Waseem, S., Islam, N., Ul Haque, N., Zuberi, L., Khan, A., & Akhter, J. (2008). Vitamin B12 deficiency common in primary hypothyroidism. JPMA. The Journal of the Pakistan Medical Association, 58(5), 258-261. Disponible sur : https://pubmed.ncbi.nlm.nih.gov/18655403/
  • Knezevic, J., Starchl, C., Tmava Berisha, A., & Amrein, K. (2020). Thyroid-Gut-Axis: How Does the Microbiota Influence Thyroid Function? Nutrients, 12(6), 1769. DOI : 10.3390/nu12061769
  • Leung, A. M., & Braverman, L. E. (2014). Consequences of excess iodine. Nature Reviews Endocrinology, 10(3), 136-142. DOI : 10.1038/nrendo.2013.251
  • Liwanpo, L., & Hershman, J. M. (2009). Conditions and drugs interfering with thyroxine absorption. Best Practice & Research Clinical Endocrinology & Metabolism, 23(6), 781-792. DOI : 10.1016/j.beem.2009.06.006
  • McMillan, M., Spinks, E. A., & Fenwick, G. R. (1986). Preliminary observations on the effect of dietary brussels sprouts on thyroid function. Human Toxicology, 5(1), 15-19. DOI : 10.1177/096032718600500104
  • Messina, M., & Redmond, G. (2006). Effects of soy protein and soybean isoflavones on thyroid function in healthy adults and hypothyroid patients: a review of the relevant literature. Thyroid, 16(3), 249-258. DOI : 10.1089/thy.2006.16.249
  • Nagataki, S. (2008). The average of dietary iodine intake due to the ingestion of seaweeds is 1.2 mg/day in Japan. Thyroid, 18(6), 667-668. DOI : 10.1089/thy.2007.0379
  • Nitschke, U., & Stengel, D. B. (2016). Quantification of iodine loss in edible Irish seaweeds during washing, boiling and domestic processing. Food Chemistry, 156, 89-95. DOI : 10.1016/j.foodchem.2013.12.022
  • Rayman, M. P., & Bath, S. C. (2015). The new emergence of iodine deficiency in the UK: consequences for child neurodevelopment. Annals of Clinical Biochemistry, 52(6), 705-708. DOI : 10.1177/0004563215597249
  • Schomburg, L. (2011). Selenium, selenoproteins and the thyroid gland: interactions in health and disease. Nature Reviews Endocrinology, 8(3), 160-171. DOI : 10.1038/nrendo.2011.174
  • Severo, J. S., Morais, J. B. S., de Freitas, T. E. C., Andrade, A. L. P., Feitosa, M. M., Fontenelle, L. C., de Oliveira, A. R. S., Cruz, K. J. C., & do Nascimento Marreiro, D. (2019). The role of zinc in thyroid hormones metabolism. International Journal for Vitamin and Nutrition Research, 89(1-2), 80-88. DOI : 10.1024/0300-9831/a000262
  • Smyth, P. P. A. (2021). Iodine, seaweed, and the thyroid. European Thyroid Journal, 10(2), 101-108. DOI : 10.1159/000512971
  • Taylor, P. N., Albrecht, D., Scholz, A., Gutierrez-Buey, G., Lazarus, J. H., Dayan, C. M., & Okosieme, O. E. (2018). Global epidemiology of hyperthyroidism and hypothyroidism. Nature Reviews Endocrinology, 14(5), 301-316. DOI : 10.1038/nrendo.2018.18
  • Vandevijvere, S., Amsalkhir, S., Mourri, A. B., Van Oyen, H., & Moreno-Reyes, R. (2012). Iodine deficiency among Belgian pregnant women not fully corrected by iodine-containing multivitamins. European Journal of Nutrition, 51(7), 819-826. DOI : 10.1007/s00394-011-0267-3
  • Wichman, J., Winther, K. H., Bonnema, S. J., & Hegedüs, L. (2016). Selenium supplementation significantly reduces thyroid autoantibody levels in patients with chronic autoimmune thyroiditis: A systematic review and meta-analysis. Thyroid, 26(12), 1681-1692. DOI : 10.1089/thy.2016.0256
  • Zimmermann, M. B., & Andersson, M. (2021). Assessment of iodine nutrition in populations: past, present, and future. Nutrition Reviews, 79(Suppl 2), 49-58. DOI : 10.1093/nutrit/nuab047
  • Zimmermann, M. B., & Boelaert, K. (2015). Iodine deficiency and thyroid disorders. The Lancet Diabetes & Endocrinology, 3(4), 286-295. DOI : 10.1016/S2213-8587(14)70225-670225-6)

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