Iodine deficiency - daily requirement, iodine deficiency and iodine excess

Iodine is an essential trace element that plays a key role in human health and well-being. Although our bodies need only small amounts, the effects of its presence—or its absence—are far-reaching. It is therefore important to understand what iodine is, where we find it, how much we need, and what role it plays in our bodies. Read on if you would like a comprehensive overview of iodine, its functions, daily requirements, the consequences of deficiency or excess, and the role of iodine in specific health conditions such as Hashimoto's disease.

Table of Contents 

• What is iodine?
• Why does our body need iodine?
• How much iodine should we consume daily?
• Which foods contain iodine?
• Why is salt enriched with iodine?
• What should be considered when consuming iodine?
• What is iodine deficiency?
• What is iodine excess?
• Summary

What is iodine?

Iodine is a chemical element and mineral that occurs in trace amounts in our body and is essential for various functions. It is especially known for its role in the production of thyroid hormones, which regulate numerous processes in the body, including metabolism and growth. Unlike some other essential nutrients, the human body cannot produce iodine on its own. That is why iodine must be supplied through food or, if necessary, supplements (Britannica, 2023).

Why does our body need iodine?

Iodine is an indispensable component in our body because it plays a key role in the production of the thyroid hormones thyroxine (T4) and triiodothyronine (T3), which are essential for our health and well-being. It is important to understand that iodine itself does not carry out the many functions discussed below—it enables the production of the hormones responsible for these tasks. The process of thyroid hormone production is complex and takes place mainly within the thyroid gland, a butterfly-shaped gland in our neck. Iodine is actively transported from our bloodstream into the thyroid and incorporated into the T4 and T3 hormones. Iodine is thus an essential building block of these hormones, which is why adequate iodine intake is crucial to maintain a normal hormone balance and thereby a wide range of bodily functions (NHS, 2020).

The thyroid hormones, whose production depends on iodine, have the following important functions:

• Regulation of metabolism: Thyroid hormones control the rate at which your body uses energy from the food you consume. This process, known as metabolism, affects a variety of bodily functions, including your heart rate, how quickly you burn calories, and even your concentration.

• Growth and development: Thyroid hormones are essential for the growth and development of organs. This is especially important during pregnancy and childhood, as they contribute to brain and nervous system development.

• Body temperature and energy levels: Thyroid hormones help regulate body temperature and maintain energy levels. Without an adequate amount of these hormones, one may experience sensitivity to cold and constant fatigue.

Source: Cleveland Clinic, 2022

How much iodine should we consume daily?

The recommended daily intake of iodine varies by age, gender, and life stage. It is given in micrograms and is shown in the following table:

These values are general recommendations and may vary individually. It is always advisable to consult a doctor or nutritionist regarding your personal iodine requirements (NIH,2022).

Which foods contain iodine?

Iodine is found in various foods, especially those derived from the sea. However, the actual amount of iodine in food can vary depending on the iodine content of the soil and water where the food is grown or harvested. The following foods are rich in iodine, with quantities based on typical serving sizes:

• Sea fish: Ocean fish such as cod, tuna, and haddock are rich in iodine. An average portion (85g) of cod can contain about 99 micrograms of iodine.

• Seaweed: Seaweed and kelp are particularly high in iodine, although the amount can vary greatly. An average serving (1g) of dried seaweed may contain about 1,500–2,000 micrograms of iodine.

• Dairy products: Milk and dairy products contain notable amounts of iodine. One cup (240ml) of milk provides about 56 micrograms of iodine.

• Eggs: Eggs, especially the yolk, contain iodine. One large egg provides around 24 micrograms of iodine.

• Iodized salt: Iodized salt is specifically enriched with iodine to prevent deficiency. Half a teaspoon of iodized salt contains approximately 71 micrograms of iodine.

• Seafood: Shellfish, particularly shrimp and mussels, are also rich in iodine. An average serving (85g) of shrimp contains about 35 micrograms of iodine.

Sources: NIH, 2022; Todd, 2021

Why is salt enriched with iodine?

Iodized salt is the result of efforts to prevent iodine deficiency disorders in the population. In many parts of the world, soil is low in iodine, meaning that crops and livestock raised there do not contain sufficient iodine. This can lead to iodine deficiency in the population. By enriching salt—an item widely and regularly consumed—with iodine, it is ensured that people receive adequate amounts of iodine to effectively prevent deficiency disorders (Ajmera, 2018).

What should be considered when consuming iodine?

Although seaweed and iodized salt are essential sources of iodine, it is important to consume them in moderation. Seaweed, especially brown and red algae, can contain extremely high levels of iodine, which may lead to iodine excess if consumed excessively. Similarly, iodized salt can exceed the recommended daily iodine intake if overused. Therefore, it is advisable to balance iodine intake from various sources (Mayo Clinic, 2016; NIH, 2022).

What is iodine deficiency?

Iodine deficiency occurs when the body does not receive enough iodine to maintain normal function. This can result in reduced production of thyroid hormones, leading to various health issues including thyroid enlargement (goitre), metabolic disorders, and developmental problems in unborn babies during pregnancy (American Thyroid Association, 2023). 

What causes iodine deficiency?

Iodine deficiency can arise for various reasons. Some of the most common causes include:

• Dietary habits: A lack of iodine in the diet is a leading cause. Populations that do not regularly consume seafood or that follow low-salt diets are at increased risk.

• Geographical factors: Certain regions, such as mountainous or flood-prone areas, have iodine-poor soil, resulting in low iodine content in local foods.

• Pregnancy and breastfeeding: The need for iodine increases during these phases, as the baby or nursing infant also requires iodine. Without adequate intake, deficiency may occur.

• Selenium deficiency: Selenium is an important element for proper thyroid function and iodine utilization. A deficiency can thus result in a functional iodine deficiency.

• Certain medications and illnesses: Some medications and diseases affect the body's ability to absorb or use iodine. These include thyroid diseases such as Hashimoto’s thyroiditis and Graves’ disease, genetic disorders, and certain kidney or gastrointestinal diseases.

• Excessive consumption of specific foods: Certain foods, known as goitrogens, may impair iodine absorption in the thyroid. These include cruciferous vegetables, soy, peanuts, and flaxseed. Excessive consumption of these can, in rare cases, contribute to deficiency.

• Exposure to certain chemicals: Chemicals like perchlorate and thiocyanate may compete with iodine and inhibit its uptake by the thyroid.

Source: Zimmermann, 2009

Please note that iodine deficiency can pose a serious health risk and should be treated by a medical professional if you suspect you have symptoms.

What are the symptoms of iodine deficiency?

Iodine deficiency can cause a range of symptoms, which are often non-specific and difficult to diagnose. These may include:

• Fatigue and weakness

• Weight gain

• Sensitivity to cold

• Dry skin and hair

• Muscle and joint pain

• Depression and difficulty concentrating

• In advanced cases, goitre (thyroid enlargement)

It is important to note that these symptoms may also indicate other health conditions and should always be evaluated by a doctor (Burgess, 2018). 

What are the consequences of iodine deficiency?

Prolonged iodine deficiency can lead to various health issues, including:

• Goitre: Iodine deficiency may cause the thyroid to enlarge in an attempt to absorb more iodine from the blood.

• Hypothyroidism: A chronic lack of iodine may impair the production of thyroid hormones, resulting in symptoms such as fatigue, weight gain, cold intolerance, and depression.

• Developmental disorders in children: In children—especially fetuses and infants—iodine deficiency can cause growth delays and cognitive impairments. These effects are often irreversible.

• Pregnancy complications: In pregnant women, iodine deficiency may lead to miscarriage, premature birth, or birth defects. Ensuring sufficient iodine intake during pregnancy is therefore essential.

Source: NIH, 2022

How is iodine deficiency diagnosed and treated?

Iodine deficiency can be diagnosed through blood tests that measure thyroid hormone levels. If necessary, urinary iodine levels can also be tested. Treatment generally involves increasing iodine intake through diet or supplements. In severe cases, medication may be necessary. It is important that treatment is supervised by a doctor to avoid overdose (Cleveland Clinic, 2022).

Want to check for yourself?

The Homed-IQ thyroid test offers an important way to assess the health of your thyroid and detect potential problems such as iodine deficiency or excess early on. Since iodine plays a crucial role in hormone production, an imbalance can lead to various health issues. This test measures key thyroid markers such as TSH, T3, and T4, helping you evaluate your thyroid function and make informed decisions about your health and potential next steps.

What is iodine excess?

While iodine deficiency can cause health problems, so can iodine excess—also known as iodine toxicity or overdose. It is important to note that iodine excess is usually caused by over-supplementation and rarely by food consumption alone.

What are the symptoms of iodine excess?

• Hyperthyroidism: This condition involves an overactive thyroid that produces too much hormone. Symptoms include weight loss, rapid heart rate, nervousness, and sweating.

• Iodine acne: Some people may develop acne-like skin conditions due to iodine excess.

• Iodism: Extremely high doses can cause symptoms such as a metallic taste, increased salivation, headaches, and skin rashes.

Complications may also occur in individuals with pre-existing thyroid disorders. People with autoimmune thyroid disease such as Hashimoto's thyroiditis or thyroid nodules may be more sensitive to iodine and experience worsened symptoms (Linus Pauling Institute, 2023). 

Iodine and Hashimoto’s disease

Hashimoto's thyroiditis is an autoimmune disease in which the immune system attacks the thyroid gland, leading to permanent hypothyroidism. Evidence suggests that high iodine intake may trigger or worsen the onset of Hashimoto’s thyroiditis, especially in genetically predisposed individuals. Therefore, people with Hashimoto’s are often advised to moderate their iodine intake (NIDDK, 2021).

How is iodine excess diagnosed and treated?

Diagnosis of iodine excess is similar to that of deficiency and includes tests to determine the body's iodine levels. This can be done through a urine test measuring iodine excretion. Blood tests may also be used to assess thyroid hormone levels, as iodine excess can lead to both over- and underproduction of these hormones.

Treatment focuses primarily on reducing iodine intake, which can be achieved by stopping iodine supplements or adjusting the diet. In some cases, medication may be necessary to regulate thyroid function. It is essential that treatment is supervised by a doctor (Southern & Jwayyed, 2022). 

Summary

Iodine is a vital trace element that plays an important role in our body, especially in the production of thyroid hormones. Deficiency can lead to various health problems such as goitre and hypothyroidism, while excess iodine can also be harmful. It is therefore important to ensure a balanced iodine intake. If you suspect an iodine deficiency or excess, always consult a doctor.