Are you feeling constantly weak? Fatigued? Or do you feel your heart racing or palpitating? Are you losing weight despite not trying? These are some signs that you might be missing out on an important nutrient in your body- iodine. 

Iodine is an essential trace element that is needed by the body. It is found in fish, iodized salt and other marine foods. Apart from being naturally present in food, it is also available as a dietary supplement. 

What does iodine do for the body? Iodine is an important component of hormones released from the thyroid gland. This gland is a small, butterfly shaped structure found just beneath your voice box and in front of your neck. The thyroid gland is part of the endocrine system, a system of glands that release hormones that control the different functions of the body. 

The main job of thyroid gland is to control your metabolic rate or how fast or slow your metabolism should go. Metabolism is defined as the process in which your body transforms carbohydrates or fats consumed from food into energy. This process of breaking down food for energy is necessary to help the body function. Without energy, the body stops to function since all cells require energy to perform its roles and activities. Hence, when the thyroid gland lacks iodine to produce its hormones, your body will not work properly. 

To properly understand the benefits of iodine, it is necessary to determine what the thyroid gland does. 

What are the functions of the thyroid gland? 

The thyroid gland is an endocrine gland and produces hormones needed for metabolism or the break down of food to form energy. Here are important hormones produced by the thyroid gland. 

• Thyroxine 4 (T4)- The main hormone released from the thyroid gland is called thyroxine 4. Once this hormone is released from the thyroid gland to the bloodstream, it is converted to triiodothyronine or T3. However, to exert its effects on your metabolism, T4 needs to be converted to T3. 
• Triiodothyronine (T3)- Compared to T4, the thyroid gland produces less T3 directly. Instead, T4 is converted to T3, depending on the body’s needs. However, T3 has greater effects on your metabolism compared to T4. 
• Reverse triiodothyronine (RT3)- this hormone is produced in very small amounts and reverses the effects of triiodothyronine or T3. 

Iodine is needed to make the thyroid hormones. Hence, you should take appropriate amounts of iodine from your diet to help your body make these important thyroid hormones. Once iodine is taken by the body, this is trapped by the thyroid glands and transformed into the thyroid hormones. 

Too much or too little iodine can affect the hormone levels that the thyroid produces and releases into the bloodstream. 

Here are some functions of our thyroid hormones: 

• Regulates heart rate 
• Regulates breathing 
• Use of energy or metabolism of the body
• Affects digestion 
• Affects brain development 
• Maintains skin and bone functioning 
• Affects mental activity 
• Influences fertility 

The thyroid hormones also regulate biochemical reactions that are necessary in producing or synthesising proteins and carbohydrates. Thyroid hormones are essential in infants or fetuses since they are involved in the proper development of the skeletal system and the nervous system of the unborn babies and newly born infants. Obtaining sufficient iodine is necessary for all people, especially for pregnant women and infants. 

What are the benefits of iodine? 

Iodine is found in water and in the soil. Food grown in iodine-rich soil have trace amounts of this important nutrient. Meanwhile, fishes and other marine organisms harvest iodine from the seawater. Hence, these fishes and marine organisms are good sources of iodine. 

Proper thyroid function 

Iodine is essential in the production of thyroid hormones. The lack of iodine can result in low production of thyroid hormones needed to promote metabolism of carbohydrates and proteins. 

Proper development of fetuses during pregnancy 

Pregnancy is a crucial stage in both the mother and infant’s lives since this is the stage where development of the unborn child should be optimal to ensure a healthy, safe pregnancy and birth. During pregnancy, the baby’s brain develops and would require essential nutrients for optimal development. Iodine is one of the many nutrients that the baby’s brain needs for development. 

Studies [1] have shown that women who have insufficient iodine in their bodies during pregnancy tend to give birth to babies with poor cognitive development and intellectual delays. These children also tend to have lower IQs, which is the measurement of intelligence. In contrast, women with sufficient iodine during pregnancy give birth to children with proper brain development.

Apart from poor brain development and intellectual disability, severe lack of iodine during pregnancy can lead to cretinism. Cretinism is a condition caused by severe iodine deficiency and is characterised by severe physical and mental retardation. This condition is irreversible soon after birth even if the infant receives iodine or thyroid hormones. However, this condition can still be reversed during gestation or when the mother is still pregnant and corrects the iodine deficiency with supplements very early in the pregnancy. 

Apart from pregnancy, mothers who are breastfeeding also require higher amounts of iodine. Breastfeeding mothers need to supply their infants with sufficient iodine and other minerals through their breastmilk for optimal brain development of their babies. 

Improvements of cognitive functions and brain development in children 

Iodine optimizes brain development not only in infants but also in growing children. Young children who do not receive sufficient iodine are at increased risk of cognitive delays or delays in brain development and intellectual disabilities. 

The World Health Organization [2] has stated that deficiency in iodine is the main cause of brain damage in children. This deficiency results in impairment of cognitive functioning of the children and delay in motor development. In turn, these delays and impairment in brain development affects the performance of the child at school. The effects extend into adulthood. Adults who are deficient in iodine at childhood have poor productivity and have difficulties finding employment. The WHO states that those who are iodine-deficient may forfeit at least 15 IQ points. Across the world, nearly 50 million people suffer from some form of brain damage due to iodine deficiency. 

Young children are at increased risk of brain damage due to lack of iodine since the brain still requires iodine for development during their first two years of life. Notably, a deficiency of this nutrient in children results in disorders such as hypothyroidism. 

Iodine deficiency is highly preventable at a low cost. In developing countries, the least expensive method in correcting iodine deficiency disorder is through simply iodizing table salt. It has been shown that when salt iodization is implemented for at least a year, thee improvement in the iodine status of the whole population is overwhelming. 

Healthy birth weight 

A healthy birth weight gives children a healthy start in life. Pregnant women should receive sufficient iodine during pregnancy to ensure a healthy birth weight of their babies. Pregnant women who develop goiter, which is caused by iodine deficiency, could give birth to babies with low birth weight. However, supplementation with iodine can correct this deficiency and help improve the birth weight of their unborn babies. 

Lowers risk of developing goiters 

A goiter refers to the enlarged thyroid gland. Goiter results from an underactive thyroid gland or an overactive thyroid gland. When there is insufficient iodine levels in the blood, the body reacts by increasing the levels of thyroid stimulating hormones (TSH). Once TSH is elevated, this can lead to enlargement of the thyroid gland or goiter. The body attempts to get more iodine from the blood to produce the thyroid hormones and as a result, the gland enlarges. 

Although the most common cause of goiter is iodine deficiency, goiter can also be caused by diseases such as Grave’s disease or Hashimoto’s disease. In rare instance, goiter can be caused by a tumor, injury, or genetic defect. However, for dietary-related goiters, supplementation with iodine is the best way to manage and treat goiters. 

Potential treatment for fibrocystic breast disease 

Iodine deficiency is associated with fibrocystic breast disease. This disease can be treated effectively through supplementation with iodine [3]. Fibrocystic disease is characterised by painful lumps in the breasts. However, this disease is not cancerous and  affects approximately 50% of women of reproductive age. Although this disease is non-cancerous, it is still associated with increased risk of developing breast cancer. 

Potential treamtent for thyroid cancer 

Thyroid cancer is a malignant disease characterised by prevalence of cancer cells in the thyroid gland tissues. 

Risk factors for thyroid cancer include the following: 

• A family history of thyroid cancer or thyroid disease
• Presence of genetic conditions such as multiple endocrine neoplasia type 2 A syndrome (MEN2A), multiple endocrine neoplasia type 2B syndrome, familial medullary thyroid cancer (FMTC)
• A history of goiter 
• Exposure to radiation to the neck or head as a child or infant
• Gender- being female 
• Age – those between 25 years old to 65 years old 
• Ethnicity – being Asian 

Radioactive iodine has the potential to treat thyroid cancer. Radioactive iodine is absorbed well by the thyroid. Once this type of iodine is taken in, it can destroy cancerous thyroid cells that are not removed during surgery. Administration of this type of iodine is associated with increased lifespan in people who have thyroid cancer that has spread to different parts of the body. 

Considering the importance of iodine in the body, it is important to examine the common food sources of iodine. 

What food sources are rich in iodine? 

Seafoods and vegetables are excellent sources of iodine. Here are some examples of plants or seafoods rich in iodine: 

• Seaweed (kombu, kelp, nori, wakame) 
• Shellfish, fish (shrimp, oysters, canned tuna, cod) 
• Fortified infant formula 
• Iodized table salts 
• Chicken 
• Eggs
• Dairy (yogurt, cheese, milk) 
• Beef liver 
• Lima beans 
• Prunes 

Seaweeds are rich in iodine since the sea contains iodine. As seaweeds grow, they also absorb the iodine present in the waters. Apart form being rich in iodine, it is also a good source of antioxidants, vitamins and minerals. While seaweeds have high amounts of iodine, the amount present in each seaweed varies according to location and variety. To date, there are three popular types of seaweeds. These include the wakame, nori and komby pelp. 

If you are fond of eating sushi rolls, the green wrappings of these rolls are called nori, which is a type of seaweed. Nori contains at least 29% of the recommended dietary allowance for iodine. Typically, it contains at least 16 to 43 mcg of iodine. Next to nori is the wakame, a brown seaweed that is slightly sweet to the taste. This type of seaweed is commonly used in making miso soup. Depending on where it is grown, its iodine content may be high or low compared to nori. Wakami that is grown in Australia and New Zealand have lower amounts of iodine compared to wakami grown in Asia. 

Another common seaweed that contains high amounts of iodine includes the kombu kelp. This seaweed is colored brown and is sold as dried seaweed. Of the three popular seaweeds, kombu kelp has the highest amount of iodine. It is also used to make Japanese soup stock. 

Meanwhile, codfish is another source of iodine. Fishes that are low in fats are found to be high in iodine. An 85 grams of cod or about one serving of this fish contains at most 66% of the recommended dietary allowance for iodine. However, the location where codfish is grown dictates the amount of iodine it contains. 

Tunafish, similar to codfish, has low fats and high iodine content. Aside from being rich in proteins, it is an excellent source of the B vitamins, potassium and iron. It also contains omega-3 fatty acids, which are important in preventing cardiovascular diseases or lowering the risk of heart diseases. 

Dairy products are another good sources of iodine. Milk that are fortified with iodine contains at most 112% of the recommended dietary allowance for iodine. Next to milk, yogurt contains about 50% of the recommended dietary allowance for iodine. Cottage cheese is another excellent source of iodine. Meanwhile, eggs are also good sources of iodine. It contains at least 16% of the recommended dietary allowance for iodine. 

Iodized table salt contains 42 mcg of iodine. Iodization of table salt is an effective way to correct population-based iodine deficiency. 

Another seafood rich in iodine includes the shrimp. It is likewise high in protein but low in fats. It also contains selenium, phosphorus and vitamin B12. Three ounces of shrimp provides 23% of the recommended dietary allowance for iodine. 

Lima beans provide 10% of iodine’s RDA. These beans can be used to replace fish meat and shrimps as sources of iodine for strictly vegan people. Apart from Lima beans, prunes can be another source of iodine for people who are vegans. Prunes are rich in fiber, potassium, iron and vitamins K and A. 

What are the side-effects of iodine? 

Taking iodine at very high amounts could result in health issues and thyroid problems. It is reported that greater than 1,100 mcg of iodine can lead to serious side effects for both men and women. 

Excessive iodine supplementation can result in the following: 

• Metallic taste in the moth 
• Diarrhea 
• Upset stomach 
• Headache 
• Stomach pain 
• Runny nose 
• Iodine-induced hyperthyroidism 
• Autoimmune thyroid disease 

Iodine can also interact with other medications. Hence, always consult your doctor when you are taking iodine supplements and is prescribed with lithium. Lithium is a drug for treatment of mental health conditions such as hypomania, mania and bipolar disorder. Iodine can also interact with the absorption of certain medications for high blood pressure, heart problems and thyroid problems. 

Research and dosage 

The recommended dietary allowance (RDA) for iodine has been established by the National Institute of Health in the US [4]. 

The adequate intake (AI) for infants from birth to six months is 110 mcg/day for both male and female children. From seven months to 12 months, the AI is 130 mcg/day for both gender. The RDA for children aged one to three years is 90 mcg/day. Children aged four to eight years old need to take 90 mcg of iodine per day while children aged 19-13 years have a RDA of 120 mcg. In adolescents aged 14-18 years old, the RDA is 150 mcg/day for both males and females. For adults aged 19+ years old, the RDA for iodine is 150 mcg. In pregnant women, the RDA increases to 220 mcg and during lactation, this further increases to 290mcg/day. 

Both the United Nations Children’s Fund (UNICEF) and the World Health Organisation recommend a slightly higher iodine intake for pregnant women at 250 mcg per day. 

A deficiency in iodine leads to stunted growth in children, mental retardation and difficulties in problem solving, reading, writing, talking and social skills. It can also lead to stillbirths and miscarriage. In adults, lack of iodine results in hypothyroidism where thyroid hormones become deficient. Low levels of thyroid hormones can disrupt metabolic functions responsible for regulating body temperature, weight and heart rate. Hypothyroidism can also lead to development of goiter. 

Signs of hypothyroidism include the following: 

• Weight gain
• Infertility 
• Constipation 
• Sensitivity to cold 
• Lethargy
• Fatigue 
• Difficulties in memorizing and performing higher cognitive function tasks 
• Weakness 

Those who are risk of iodine deficiency include the following: 

• Pregnant women with poor dietary intake of iodine 
• Adults who do not use iodized salts and have deficient iodine levels in the blood 
• Vegans who fail to incorporate foods that are high in iodine 
• People who live in mountainous regions where the soil has low iodine levels 

Current research has focused on thyroid cancer and how to potentially prevent this condition from happening. Thyroid cancer is is recognized as the most common for of cancer of the endocrine system [5]. Many countries have shown an increasing prevalence of this type of cancer. However, it is also presumed that this increased prevalence may be due to better screening and assessment tools for thyroid cancer. In the US, thyroid cancer is the fifth most common cancer among women. 

Iodine is critical in the synthesis of thyroid hormones. It is recognized that iodine has a u-shaped relationship with thyroid disease. This indicated that too high and too little amounts of iodine intake will lead to goiter and other thyroid diseases. Chronic iodine deficiency or high iodine intake has been associated with development of goiter. This is a cause for concern as goiter is associated with increased risk of developing to a thyroid cancer. 

The exact relationship between iodine and thyroid cancer formation is not clear. As one study [6] reported that a diet high in iodine was protective against thyroid cancer. Specifically, this study, which was published in the Thyroid journal, observed that diet high in shellfish and fish was associated with reduced risk of thyroid cancer. However, a case control study [7] reported that high consumption of food rich in iodine, such as seafoods, resulted in increased risk of thyroid cancer in women but not in men. Authors of this study could not verify why women are at increased risk of thyroid cancer following a diet high in seafoods. 

A third study [8], however, did not find any relationship between dietary iodine intake and thyroid cancer. This study, which was published in the Cancer Causes and Control journal, reported that high consumption of seafoods and fishes was not associated with thyroid cancer. Instead, the study authors observed that women with low iodine intake who consumed high amounts of cruciferous vegetables were at greater risk of thyroid cancer. 

In summary, iodine is crucial in the production and synthesis of thyroid hormones. These hormones are involved in various metabolic processes. Low amounts of these hormones leads to a condition called hypothyroidism. Iodine is crucial in brain development in fetuses and during early childhood. Iodine deficiency during pregnancy increases the risk of giving birth to children with mental retardation and growth stunting. In worse cases, severe iodine deficiency results in cretinism. Meanwhile, excessive iodine intake leads to thyroid problems. Finally, it is crucial to follow the recommended dietary allowance for iodine to reap the benefits of this important nutrient in the body. 

[1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3257674 
[2] https://www.who.int/news-room/questions-and-answers/item/nutrition-effects-of-iodine-deficiency
[3] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5327366
[4] https://ods.od.nih.gov/factsheets/Iodine-HealthProfessional/ 
[5] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8212601/ 
[6] http://www.ncbi.nlm.nih.gov/pubmed/22280227 
[7] https://pubmed.ncbi.nlm.nih.gov/2102295/ 
[8] https://pubmed.ncbi.nlm.nih.gov/20361352/ 

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