Iodine-rich foods: A key component of a balanced diet

Iodine is an essential trace element vital for producing thyroid hormones like triiodothyronine (T3) and thyroxine (T4). These hormones play a crucial role in metabolic regulation, protein synthesis, and the development of the nervous system in fetuses and infants [1].

The World Health Organization (WHO) reports that nearly 1.88 billion individuals, including 241 million school-age children, are not consuming enough iodine [2].

This deficiency is the leading cause of preventable brain damage and cognitive impairments during childhood, potentially reducing a child’s school performance and an adult’s productivity and employability by up to 15 IQ points.

Nearly 50 million people globally are affected by varying degrees of brain damage due to inadequate iodine intake, emphasizing the critical need for ensuring sufficient iodine levels in the diet.

What are the physiological functions of iodine? 

Iodine plays several vital roles in the human body, primarily through its involvement in thyroid hormone production. Here are the key physiological functions of iodine:

  1. Thyroid hormone production – Iodine is a critical component of the thyroid hormones, thyroxine (T4) and triiodothyronine (T3) [3]. These hormones regulate various metabolic processes, including energy production, body temperature, and heart rate.
  2. Neurodevelopment – Adequate iodine levels are essential for the proper development of the nervous system in fetuses and infants [4]. It supports brain development, cognitive function, and neurological health.
  3. Immune system regulation – Iodine has a role in the immune system, where it supports immune response and helps in the functioning of the immune cells.
  4. Reproductive health – It is important for reproductive health, playing a role in the normal reproductive processes in both males and females.

What are the sources of iodine? 

The soil in different parts of the world holds varying amounts of iodine. Hence, the iodine content found in crops also varies.

In areas where the soil has insufficient iodine, governments have introduced policies that allow the iodine fortification of salt. These salt iodization programs have reduced the prevalence of iodine deficiency globally. 

Iodine is found in sea vegetables and animal protein foods. It is also found to a lesser extent in fortified foods such as milk, cereals, and loaves of bread. 

Here are some excellent sources of iodine [5], [6]: 

1. Seaweed

Seaweed remains a good source of vitamins, minerals, and antioxidants. It is also one of the best sources of iodine.

However, the amount of iodine in seaweeds varies by location and region. There are at least three popular varieties of seaweed:

  • Nori – A type of red seaweed commonly used in sushi rolls. Its iodine content ranges from 16-43 mcg per gram, which amounts to approximately 11-29% of the RDA. 
  • Wakame – A brown seaweed with a slightly sweet flavor and is commonly used in miso soup. Its iodine content varies depending on where it is grown. For example, wakame grown in Asia contains higher amounts of iodine than in New Zealand and Australia. 
  • Kombu kelp – A brown seaweed sold as a fine powder or dried seaweed. Compared to other seaweed, kombu kelp has the highest amount of iodine. It is an essential ingredient for dashi, a Japanese soup stock.
Iodine-rich foods Seaweed

2. Cod 

Codfish have low fats but high iodine. It has been shown that fish low in fats are rich in iodine. For example, 85 grams of cod contains approximately 42 to 66% of the RDA for iodine.

However, similar to seaweeds, the amount of iodine in cod varies according to the region and area where it is grown and whether it is wild-caught or farm-raised. 

3. Dairy 

In Western diets, dairy remains one of the essential sources of iodine. A cup of milk can contain approximately 59 to 112% of the RDA for iodine. Meanwhile, a cup of yogurt contains at least 50% of the RDA for iodine.

Apart from milk and yogurt, cheese also has high amounts of iodine. However, its iodine content varies according to the type of cheese. Cottage cheese has the best iodine source compared to other cheese types. 

4. Iodized salt 

One-fourth of a teaspoon of iodized salt has about 71 mcg of iodine, equivalent to 47% of the RDA. 

5. Eggs

Eggs are good sources of iodine. A large egg has approximately 16% of the RDA of iodine since it contains 24 mcg of iodine. A whole egg is also an excellent source of vitamins, minerals, and protein. However, most of these nutrients are found in the yolk of the egg. 

6. Tuna 

Tuna is a high-protein, low-calorie or low-fat, and iodine-rich fish source. It is a good source of minerals and vitamins such as B vitamins, iron, and potassium. It is also an excellent source of omega-3 fatty acids, which have been shown to lower the risk of cardiovascular diseases. 

7. Shrimp 

Shrimp is another excellent source of iodine. It is also a protein-rich and low-calorie food. It is high in vitamin B12, phosphorus, and selenium.

Like other marine organisms, shrimps absorb iodine that is naturally present in seawater. Three ounces of protein give at least 23% of the RDA for iodine or about 35 mcg. 

8. Lima beans 

These beans are commonly grown in South America and are good magnesium, folate, and fiber sources. Apart from preventing the risk of cardiovascular diseases, these beans are good sources of iodine for vegans.

However, the amount of iodine in Lima beans varies according to the amount in the soil, cultivation practices and the fertilizers used. On average, a cup of these beans provides 10% of the RDA for iodine or about 16 mcg of iodine. 

9. Prunes

Like Lima beans, prunes are also good sources of iodine for vegans. Five dried prunes contain 9% of the RDA for iodine. Besides fiber, it is rich in iron, potassium, and vitamins A and K. 

What are the recommended amounts of iodine? 

The Recommended Dietary Allowance (RDA) for iodine in women 19 years old and older and adult men is 220 mcg daily. However, the RDA for pregnant women is higher at 290 mcg daily.

The tolerable upper intake level for lactating and pregnant women is 1,100 mcg daily. This level, while very high, does not lead to adverse effects. A daily intake higher than 1,100 mcg could lead to adverse effects. 

What are the signs of iron deficiency? 

Since iodine regulates metabolism, it is critical in the functioning and growth of cells. It helps the body convert food into energy. A deficiency of this essential element can prevent normal development and growth. 

In children, deficiency in iodine leads to the following: 

  • Difficulties in talking, writing, reading, social skills, and problem-solving 
  • Stunted growth 

In pregnant women, iodine deficiency can lead to stillbirth or miscarriage. In adults, a deficiency of iodine (less than 10-20 mcg intake of iodine daily) can lead to inadequate thyroid hormone production, leading to hypothyroidism.

When individuals have hypothyroidism, this disrupts normal metabolic functions, such as regulating body weight, body temperature and heart rate. Goiter often develops during hypothyroidism. Other signs of this condition include the following: 

  • Dry skin and hair 
  • Sensitivity to cold 
  • Constipation 
  • Weakness
  • Fatigue, lethargy 
  • Weight gain 

People at risk of iodine deficiency include individuals who do not use supplements that contain iodine or do not use iodized salt.

Pregnant women with poor iodine intake are also at risk of iodine deficiency. In addition, vegans who do not consume animal food and people living in areas with deficient iodine levels in their soil, such as those in mountainous regions. 

What are the signs of iron deficiency? 
Photograph: mstandret/Envato

In closing

Iodine-rich foods play a crucial role in maintaining optimal health, contributing to thyroid function, brain development, and metabolism. 

Including eggs, dairy, fish, and seaweed in your diet can help meet daily iodine requirements, particularly for those with increased needs or dietary restrictions. Supplements offer a reliable alternative when dietary sources are insufficient.

Prioritizing these sources ensures the body’s essential iodine levels are maintained, promoting vitality and supporting long-term well-being.

FAQs

Why is iodine important in the diet?

Iodine is crucial for producing thyroid hormones, which regulate metabolism and are essential for developing the nervous system in infants. An adequate intake is necessary to prevent thyroid-related diseases and developmental issues.

What are the signs of iodine deficiency?

Symptoms of iodine deficiency include fatigue, weight gain, dry skin, and sensitivity to cold. Severe deficiency can lead to goiter, cognitive impairments, and, in pregnant women, complications like miscarriage.

What are the best dietary sources of iodine?

Seafood, dairy products, and iodized salt are excellent sources of iodine. Seaweed, fish, and dairy are rich in iodine, which can also be supplemented with iodized table salt.

How can vegetarians and vegans get enough iodine?

Vegetarians and vegans can obtain iodine from plant sources like prunes and Lima beans, as well as from iodized salt and supplements. It’s important to ensure these foods are included regularly in their diets.

[1] https://etj.bioscientifica.com/view/journals/etj/11/1/ETJ-21-0035.xml\
[2] https://www.who.int/news-room/questions-and-answers/item/nutrition-effects-of-iodine-deficiency
[3] https://www.hsph.harvard.edu/nutritionsource/iodine/
[4] https://www.who.int/tools/elena/bbc/iodine-pregnancy
[5] https://www.webmd.com/diet/foods-high-in-iodine
[6] https://www.healthdirect.gov.au/foods-high-in-iodine

Photograph: Masson-Simon/Envato
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