Food Sources High In Iodine

Introduction

Importance of iodine in the diet

The food that we eat every day is what determines our health. This is one of the reasons why a balanced diet must be considered for a daily meal plan. Micronutrients are as essential as macronutrients and must be consumed in an adequate amount. Iodine is one of the important micronutrients. 

Iodine is a non-metallic substance that is naturally found on Earth’s soil and oceans as iodate minerals.¹ Iodine is an essential mineral that is required by our body to carry out metabolic activities. 

Role of iodine in human health

Iodine has a primary function in the body- to regulate the activity of the thyroid gland. The thyroid gland is the largest endocrine gland in the body, located in the neck region, below the larynx (the voice box), and in front of the trachea (the windpipe). The thyroid gland has two lobes, one lobe on each side of the trachea. The gland consists of certain cells called follicular cells, whose role is vital for life. These cells produce and secrete the two thyroid hormones- T3 (Triiodothyronine) and T4 (Thyroxine). Iodine is required to make these two hormones. The thyroid hormones are responsible for regulating the metabolism and growth of the body.² Since iodine cannot be produced by our body, we have to obtain it through our diet.

Functions and benefits of iodine

Thyroid gland health

The thyroid gland often has functional difficulties as well, such as overactivity (Production of more hormones) and underactivity (Production of fewer hormones). The former leads to a condition called hyperthyroidism, and the latter leads to a condition called hypothyroidism.² Both these conditions are very common today. Hyperthyroidism increases the basal metabolic rate of the body, hence increasing the metabolism and temperature of the body, causing symptoms such as sweating, fatigue, muscle weakness, etc.³ Hypothyroidism, on the other hand, causes a decrease in the basal metabolic rate, thereby decreasing the temperature of the body and some symptoms like fatigue, slower heart rate, weight gain, etc.⁴

Cognitive development

The World Health Organisation (WHO) states that iodine deficiency is the principal cause of damage to the brain in childhood. This would lead to improper cognitive functions and development and difficulty in motor development as well. It is also highly advised that pregnant women incorporate enough iodine in their diet to prevent an iodine deficiency in the woman as well as the growing foetus.⁵ The growing foetus would require iodine for the brain to develop properly. Iodine deficiency during pregnancy leads to maternal and foetal hypothyroidism.⁶

Metabolism regulation

Iodine is used by the thyroid gland for the manufacture of the two thyroid hormones, and these hormones play principal roles in regulating the metabolism of the body. 

Recommended daily iodine intake

The recommended daily intake for adult men and adult women above the age of 19 is 150 milligrams. For pregnant women, the daily intake is 220 milligrams, and for lactating mothers, the daily intake is 290 milligrams.¹

Natural food sources high in iodine

We know that our body cannot make iodine, so it needs to be taken through the diet. There are plenty of food choices to pick from to supplement it through diet. Some of the sources of iodine are listed below: 

Seafood

Seafood is a good source. They are rich in iodine because they tend to absorb dissolved iodine from the sea.⁷

Fish 

Fish like Cod and Tuna, and seafood like Shrimp are fine sources of iodine. 

• Cod is a white and delicate fish. 85 grams of cod contains 42-66% of the recommended daily intake. It is also said that low-fat fish tend to have higher amounts of iodine in them.⁷ Cod offers 158 micrograms of iodine per serving.¹⁰
• Tuna is a storehouse of nutrients such as the B-complex vitamins, potassium, and iron. It is also a fish that is low-calorie, fatty, and rich in protein. 85 grams or 3 ounces of tuna fish yields 17 micrograms of iodine, which is 11% of the daily recommended intake.⁷
• Shrimp is another low-calorie option that is high in protein. 85 grams or 3 ounces of shrimp offers 23% of the daily recommended intake of iodine, which is 35 micrograms.  Shrimp is also rich in vitamin B12 and other minerals such as selenium and phosphorus.⁷ Per serving of cooked shrimp offers 13 micrograms of iodine.¹⁰

Seaweed 

Seaweed and Kelp are one of the most common marine algae, and they are known to produce 70% more oxygen than terrestrial or land plants!⁸

Seaweed is also used widely in many world cuisines, such as the Japanese. It is a repository of antioxidants, minerals, and vitamins. The amount of iodine in seaweed depends on the type and the conditions in which it was cultivated.⁷

Kombu Kelp is a popular type of seaweed, which is brown and is a really good source of iodine. With just 1 gram of Kombu Kelp, we can obtain 2,984 micrograms of iodine, which makes up the recommended daily intake of iodine by up to 2000%! But we must be careful not to over-consume it to prevent an imbalance in the body due to excess iodine. ⁽⁷⁾

Shellfish

Crustaceans, commonly known as shellfish like Lobster and Crab, may certainly be on the pricier side, but again, they are good sources of iodine.

• Lobster is a high-protein delicacy that offers 3 micrograms of iodine per 100 grams of prepared lobster.⁹
• Crab is slightly less expensive than lobsters and is packed with protein, omega-3 fatty acids, and vitamin B12. For 100 grams of blue crab, 3 micrograms of iodine can be obtained.⁹

Dairy products

Dairy and dairy products are cooking essentials with which loads of delicacies are prepared. They are also extremely nutritious sources. 

Milk

Milk is the basic form of dairy obtained from animals like cows, goats, buffalo, etc. The amount of iodine present in milk differs with the type of cattle. It is shown that 1 cup of milk offers 59-112% of iodine,⁷, which translates to 85 micrograms of iodine per cup of milk.¹⁰

Yoghurt

Yoghurt is a dairy derivative which is an immensely superior product that offers probiotic assistance to our digestive tract. It keeps our gut bacteria balanced since it contains Lactobacillus sp. 

A three-quarters cup of yoghurt contains 87 micrograms of iodine per serving.¹⁰

Cheese

Cheese is a widely loved class of aged food. There are many types of cheeses, and they vary with the method of preparation, the ingredients used, the type of inoculation culture used, and the time for ageing. Therefore, the amount of iodine would also vary in the types.

For example, 1 ounce of cheddar cheese would offer 15 micrograms of iodine,¹⁰ and one cup of cottage cheese would offer 65 micrograms of iodine, which makes it a better source.⁷

Eggs

Eggs are an excellent storehouse of nutrients. The mineral iodine is majorly found in the yolk of the egg. One large chicken egg would offer us 24 micrograms of iodine.

Iodised salt

Salt is one of the most easily obtained chemical compounds. The governments of many nations across the world have made it mandatory for salt to be iodised using potassium iodide. This is done because salt is a mandatory ingredient in cooking, and that way, our food would not be deficient in iodine. We can find both iodised and unionised types of salt in the markets today, but it has been made compulsory for those living in iodine-deficient regions to make use of iodised salt.

In a quarter of a teaspoon of salt, 71 micrograms of iodine are provided to us.⁷

Plant-based sources

Iodine-rich vegetables 

Vegetables are packed with all the major macronutrients and micronutrients and form an integral part of our diet every day. The iodine content of vegetables depends on the soil condition in which they were cultivated. A few of the iodine-rich vegetables are listed below: 

• Spinach: One of the most popularly consumed green leafy vegetables of all time. Raw spinach offers 6 micrograms of iodine per 100 grams of serving, while boiled, fresh, or frozen spinach offers 3.9 micrograms of iodine per 100 grams of serving.
• Lima Beans: These beans are rich in fibre and folate. 1 cup of cooked lima beans provides 16 micrograms of iodine.⁷

Fruits 

Fruits are an amazing go-to option for on-the-go meals like smoothies. They are a hub of essential nutrients. The iodine content of fruit also depends on the soil condition in which they were cultivated.

• Bananas: Bananas are rich in fiber which makes them apt for digestive health. These fruits contain 0.3 micrograms of iodine when consumed raw.
• Prunes: Dried plums are called prunes. Usually, prunes are either eaten or consumed as juice to relieve constipation due to the amount of fibre and sorbitol in them. Prunes contain 13 micrograms of iodine.⁷

Grains

Grains are an excellent source of carbohydrates and, thereby, are good energy sources. They also comprise two of the major staples eaten worldwide- rice and wheat. 

Whole Grains 

• Oats: A very well-known choice of breakfast is oats. 1 cup of cooked, plain oatmeal can provide around 0.3 micrograms of iodine.¹¹
• Rice: One of the most common staples in the world after wheat. Cooked brown rice offers 0.6 micrograms of iodine per 100 grams, whereas cooked and enriched white rice offers 0.5 micrograms of iodine per 100 grams.

Factors affecting iodine content in foods

Soil iodine levels

This is one of the most important factors that leads to iodine deficiency. When soil contains less iodine, the plants growing in that soil tend also to contain less iodine. Iodine-deficient soils are mostly found in mountainous areas and inland regions. Even constant leaching by water and snow often renders the soil deficient in iodine. Some examples of such places include the northern part of the Indian subcontinent, mountainous regions of Europe, the Andean region of South America, etc.¹²

To deal with this situation, the world nations have introduced the concept of iodised salt to cater to populations in all regions. Since salt is mandatory in cooking, it would compensate for the missing iodine in the food. This plan of action has reduced cases of iodine deficiency, where the major symptom is goitre.

Location and harvesting methods

To make up for the lost iodine, current research is focusing on the fortification of many vegetables with iodine. For example, the biofortification of the fruit of pepper plants has been studied and is successful. This was done by incorporating iodide solution with hydroponics.¹³

Processing and cooking effects

Processing and cooking indeed affect the iodine level in food. When some of the commonly used cooking methods like deep frying, shallow frying, pressure cooking, boiling, roasting, and cooking using the microwave were compared, it was found that shallow frying and pressure cooking showed the least loss of iodine. Boiling proved to render the food deficient in iodine at a whopping loss of iodine at 40.23%.¹⁴

Iodine deficiency and health risks

Iodine deficiency is very important to be addressed since iodine regulates the manufacture of the two thyroid hormones that control our metabolism and brain development in the young. Some of the risks that iodine deficiency can pose are listed below:

Hypothyroidism

An underactive gland leads to hypothyroidism. Some of the causes of hypothyroidism are Hashimoto’s thyroiditis, partial/complete removal of the thyroid gland, congenital hypothyroidism,⁴ secondary hypothyroidism- where the pituitary gland stops producing the Thyroid Stimulating Hormone (TSH). This hormone orders the thyroid gland to produce the thyroid hormones.¹⁵

Some symptoms of hypothyroidism include fatigue, hoarse voice, weight gain, puffy and swollen face, constipation, confusion, slow pulse, etc. People at risk for this condition include women, people over the age of 60, iodine deficiency, thyroid surgery, family history of thyroid issues, etc. 

Goiter

An enlarged thyroid gland is called a goitre. It is seen as a lump around your neck, the place where the thyroid gland is located. They are not dangerous unless they indicate thyroid cancer. There are two types of goitre- Multinodular and substernal. The former comprises many nodules, and the latter extends below the breastbone, sometimes near the lungs as well. The principal cause of goitre is iodine deficiency.¹⁶

Pregnancy complications

One of the critical points to be kept in mind during pregnancy is to supplement the daily diet with adequate iodine. Iodine deficiency during pregnancy affects the foetus greatly. Congenital Iodine Deficiency Syndrome (CIDS), or cretinism (now an obsolete term), is one of the worst conditions to affect a foetus. It is caused by extreme iodine deficiency during pregnancy. This condition is characterised by the individual’s stunted growth, in this case, dwarfism, and slow mental growth. Some of the symptoms of Congenital Iodine Deficiency Syndrome include thickened skin, enlarged tongue, issues in motor development, decreased IQ, hearing and speech defects, etc.¹⁷

Addressing iodine deficiency

Dietary changes

Iodine deficiency is best addressed through revisions in a person's diet. An iodine-deficient diet can be easily supplemented with food like tuna, milk, eggs, spinach, rice, and iodised salt. 

Iodized salt usage

The idea of iodised salt is very commendable. The government of many countries worldwide has made it mandatory for salt to be iodised and fortified using potassium iodide. This is done because salt is a mandatory ingredient in cooking, and that way, our food would not be deficient in iodine. The label of the container will specify if the salt has been iodised or not. This idea was proposed,, especially with the mountainous regions in mind. The utilisation of iodized salt has brought down the level of severe cases of iodine deficiency.

Supplements (under medical guidance)

Iodine supplements do exist, but they must be administered upon the advice of a healthcare provider only if the above alternatives are not feasible. The administration of the supplements must be moderate, as an excess can lead to toxicity. 0.5 milligrams of the supplement would be alright.¹⁸

Conclusion

Iodine is an important mineral that must be mandatorily incorporated into the diet as it is required by the thyroid gland to produce the thyroid hormones- T3 (Triiodothyronine) and T4 (Thyroxine). The two hormones regulate our metabolism, body temperature, the speed at which food moves through the gastrointestinal tract, etc. An over-functioning or an under-functioning thyroid gland is a pressing issue as it leads to the conditions of hyperthyroidism and hypothyroidism, respectively. Therefore, we must keep a check on the iodine level in our diet.

Summary

Our bodies require iodine to carry out metabolic activities. Iodine has a primary function in the body- to regulate the activity of the thyroid gland. The thyroid gland often has functional difficulties as well, such as overactivity and under-activity. The former leads to a condition called hyperthyroidism, and the latter leads to a condition called hypothyroidism. Iodine deficiency also leads to impaired cognitive functions and development and difficulty in motor development. Iodine deficiency is very important to be addressed since iodine regulates the manufacture of the two thyroid hormones that control our metabolism and brain development in the young.

The recommended daily intake of iodine for adult men and adult women above the age of 19 is 150 milligrams. For pregnant women, the daily intake is 220 milligrams, and for lactating mothers, the daily intake is 290 milligrams. There are plenty of food choices to choose from to supplement iodine through diet. Some of the sources of iodine are Fish like Cod and Tuna, and seafood like Shrimp, Seaweed, and Kelp, Lobster and Crab, milk, yoghurt, cheese, eggs, iodised salt, spinach, lima beans, bananas, prunes, oats, rice, etc. To make up for the lost iodine, current research is focusing on the fortification of many vegetables with iodine. Processing and cooking also affect the iodine level in food.

The idea of iodised salt is very commendable. The government of many countries worldwide has made it mandatory for salt to be iodised and fortified using potassium iodide. This is done because salt is a mandatory ingredient in cooking, and that way, our food would not be deficient in iodine. This idea was proposed,, especially with the mountainous regions in mind. The utilisation of iodized salt has brought down the level of severe cases of iodine deficiency. To prevent the occurrence and development of thyroid disorders, it is essential that we keep a check on the iodine level in our diet.