Iodine (I)

Iodine (I) is a chemical element with atomic number 53 in the periodic table. It’s a relatively rare element that’s naturally found in Earth’s crust. Accounting for 460 parts per billion in the layers of our planet, iodine is preceded by 60 other chemicals in relation to the natural abundance of elements. 

Classified as a member of the halogens family of elements, this nonmetal substance is the heaviest amongst all halogens. Additionally, iodine has seven valence electrons in the outermost shell of the atom, which makes it the least reactive halogen element. 

Iodine is listed as essential medicine and occurs in three aggregate states: solid, liquid, and gas.

Chemical and Physical Properties of Iodine

Atomic number53
Atomic weight126.90447 g.mol-1
ColorA dark-violet non-metallic substance with a bluish-black hue
Physical stateSolid at room temperature. It also has a liquid and a gas form.
Crystal StructureOrthorhombic
Density4.93 at 20°C
Melting point114 °C
Boiling point184 °C
Van der Waals radius0.177 nm
Ionic radius2.20 (-1) Å
Atomic radius1.32 Å
Atomic Volume25.74 cm³/mol
Most characteristic isotopeIodine-127
Electronic shell[Kr] 4d10 5s2 5p5
The energy of the first ionization1008.7 kJ.mol-1
DiscovererBernard Courtois
Oxidation States(±1),5,7
UsesRequired in small amounts by humans. Once used as an antiseptic, but no longer due to its poisonous nature.
DescriptionHeavy, colorless, odorless, noble gas.

With the periodic table symbol (I), atomic number 53, atomic mass of 126.9045 g.mol-1, and electron configuration [Kr] 4d105s25p5, iodine is a nonmetallic grayish-black substance with a strong odor that forms solid crystals with a metallic luster, as well as a violet vapor.

Out of the 53 electrons, seven of them are located in the outer shell of the iodine atom, while 46 remain in the inner shell. Hence, this septivalent element has low reactivity, since it is able to form chemical bonds with only a few other chemicals.   

It also appears in two other aggregate states: in the forms of gas and liquid. Liquid iodine is a solution that has a characteristic dark purple color, while iodine gas (I2) has a strong purple hue. 

Iodine reaches its boiling point at 184 °C, while the melting point is achieved at 114 °C. This member of the halogen family in the periodic table has an electronegativity of 2.5 according to Pauling, whereas the atomic radius according to van der Waals is 0.177 nm. 

Metallic Properties of the Nonmetallic Element 

As a metalloid, iodine has several allotropes that display the metallic properties of this nonmetallic substance when exposed to room temperature. Namely, element 53 is ductile and can be used as a semi-conductor of heat and electricity. 

The metallic characteristics of iodine are most strongly exhibited in the following iodine compounds:

  • Iodine fluoride: IF 
  • Iodine trifluoride: IF3 
  • Iodine pentafluoride IF5 
  • Iodine heptafluoride IF7
  • Iodine chloride ICl 
  • Diiodine hexachloride [ICl3]2

How Was Iodine Discovered?

The story of the iodine discovery is truly serendipitous. Namely, the discoverer of the element, Bernard Courtois, had never finished a formal education in chemistry, which is evident from his life and work:

Bernard Courtois (1777-1838)

Bernard Courtois, the discoverer of both iodine and morphine, was born in Dijon, France. There, he grew up surrounded by science as his family used to live at the Dijon Academy – a small hotel that was readapted for the purpose of accommodating scientific studies. At the same time, Courtois’ father, Jean-Baptiste, was employed at the Academy as a pharmacist. 

Courtois’ First Steps into Chemistry 

When Bernard turned twelve, the family moved to the Saint-Medard Nitrary, an experimental nitrate plant. There, Courtois and his brother supported the French revolution by making potassium nitrate for gunpowder, by processing saltpeter (a potassium nitrate mineral, KNO3).

At the age of eighteen, Courtois expressed eagerness to perfect his practice in pharmacy at a school in Auxerre, Burgundy. His mentor was M. Frémy, the grandfather of the French chemist Edmond Frémy. From Auxerre, Courtois continued his education at the École Polytechnique in Paris where he gained further valuable practice in the field of his professional interest by working at Louis Jacques Thénard’s laboratory.

Courtois’ Work at the École Polytechnique 

In 1802, Courtois dedicated his time to performing extensive studies on opium. Together with another French chemist, Armand Séguin, he succeeded in deriving scientific evidence that showed traces of morphine in the analyzed opium sample.

However, due to the failure of his father’s business in Paris, Courtois could not continue with further research on morphine with his colleague. He left the École Polytechnique in 1804 so that he could support his father during those difficult times.

How the Salpêtrier Became the Discoverer of a Chemical Element 

Upon his return to Paris, Courtois took over his father’s business as a salpêtrier and formed a family. By becoming the manager of the family’s saltpeter factory, he started using seaweed obtained from the seashores of Brittany and Normandy due to the shortage of wood ashes used in the potassium nitrate production process. 

In 1811, Courtois added sulfuric acid to the seaweed ash in order to isolate the sodium and potassium compounds. During the process of extraction of the salts, he observed that the sulfuric acid triggered corrosion of his copper vessels and created purple fumes.

This unseen purple vapor formed dark-purple crystals with a metallic luster after its condensation on the cold surface of copper vessels. Realizing that a new chemical element may be in front of him, Courtois asked the French chemists Charles-Bernard Desormes (1777-1862) and Nicolas Clément (1779-1841) to help him further analyze the purple vapor and determine its properties.

Desormes’ and Clément’s Contribution to the Discovery of Iodine

By conducting more thorough chemical analyses, Desormes and Clément produced relevant scientific evidence on the discovery of the new element – element 53. Their study on the new chemical was exhibited in 1813, at the Imperial Institute in Paris. The renewed chemists Joseph Gay-Lussac and Sir Humphry Davy also confirmed the new element upon analyzing the provided evidence. 

How Did Iodine Get Its Name?

French chemist and physicist Joseph Gay-Lussac gave the element 53 the name iodine after the Greek word ‘iodes’, which means ‘violet, purple’. The term refers to the purple vapor that condenses into dark-purple crystals in which the pure elemental form of iodine occurs. 

Where Can You Find Iodine?

Elemental iodine occurs mainly in the oceanic crust (777 ppb), followed by Earth’s crust (300 ppb), and the continental crust (119 ppb), where it can also be found in somewhat lower amounts. More than 70% of naturally occurring iodine is found in ocean sediments. While magmatic and metamorphic rocks contain low quantities of iodine, the seaweed presents the richest source of the pure form of element 53. 

Iodine is also found in deep-sea carbonates, amassed by the planktonic and shallow sea organisms. Granites, tonalites, granodiorites, and basalts contain very low quantities of iodine. In the form of iodide or iodate salts, this chemical element is highly concentrated in seaweed, sea fish, and shellfish. 

For commercial uses, iodine is obtained in several ways: by isolation of the iodine vapor from processed brine, by releasing iodine from the iodate extracted from nitrate ores, or by an ion exchange of brine.

Chile, Japan, and the United States are the world’s leading countries in iodine production. Additionally, these three countries are holders of the largest iodine reserves. 

Iodine and Health

Iodine (I) is an essential trace element for human health and the production of hormones in the thyroid gland. As a trace mineral, iodine participates in the production of triiodothyronine (T3) and thyroxine (T4). These two thyroid gland hormones are responsible for the regulation of cellular metabolism and all physiological functions, i.e.

The biological mechanisms that support the work of the body’s organs and systems. As they’re dependent on the presence of iodine molecules, these systems become dysfunctional if there is an iodine deficiency in the body.  

What is the Function of the Thyroid Gland?

Located in front of the neck (right under the anatomical structure labeled as prominentia laryngea, or ‘Adam’s apple’), the thyroid gland is the most important part of the endocrine system of our body. It’s made up of two lobes bridged by thyroid tissue referred to as isthmus. The left and right lobes of the thyroid gland are positioned symmetrically on both sides of the trachea

The thyroid gland uses iodine to secrete the hormones thyroxine (T4) and triiodothyronine (T3) into the bloodstream, which carries the hormones to all the cells in the body. In this way, the gland supports the mechanism of the cells, as well as the metabolic processes,  maturation, mental development, normal growth, oxidation (burning) of fats and protein production, use of carbohydrates and production of energy, control and regulation of the body’s temperature, and many other vital processes. 

Adequate levels of iodine in the thyroid gland are especially important for pregnant women because it ensures the normal development of the baby’s cerebrum (i.e. brain) during the pregnancy and the early life of the infant. 

Thyroxine (T4) and Triiodothyronine (T3) Hormones

While the thyroxine (T4) hormone consists of four iodine atoms, the triiodothyronine (T3) hormone has three iodine atoms in its structure. When these hormones reach the bodily tissues through the bloodstream, T4 converts into T3 inside the cells. As it’s derived from the thyroxine (T4) hormone, the triiodothyronine (T3) hormone becomes the biologically most active hormone of the thyroid gland that supports the metabolic functions of the body, as well as the mechanisms of the cells. More specifically, the T3 hormone regulates the speed of the cellular mechanisms by increasing the activity of the cells.   

What Mechanism Regulates the Secretion of the T4 and T3 Hormones?

Located under the brain and protected by the bony structure of the skull, there is a small gland that regulates the amount of T4 and T3 hormones that are secreted by the thyroid gland. This gland is called the pituitary gland. Its main function is to control and regulate the number of hormones released by the thyroid gland into the bloodstream. 

If the amount of secreted hormones is below the required level, the pituitary gland reacts by secreting the thyroid-stimulating hormone (TSH) in order to stimulate the thyroid gland for increased production of the T4 and T3 hormones. On the other hand, if the bloodstream is oversaturated with thyroxine, the pituitary gland stops secreting the thyroid-stimulating hormone (TSH) which lowers the activity of the thyroid gland. That’s how this small hormonal regulating gland controls the amount of thyroxine (T4) and triiodothyronine (T3) hormones in the body.


If the thyroid gland starts to secrete more thyroxine than the body needs, the tissues and cells become overstimulated and oversaturated with the iodine-containing hormone. This condition is called hyperthyroidism, i.e. overactive thyroid gland.

What are the Symptoms of Hyperthyroidism?

The overstimulation of the cellular metabolism by excess production of thyroxine often results in the following medical conditions:

  • Hypermetabolism;
  • Anorexia;
  • Unwanted weight loss as a result of the accelerated metabolism of the body;
  • Increased blood pressure;
  • Irregular heart rate (arrhythmia);
  • Rapid heartbeat (tachycardia);
  • Frequent mood swings;
  • Increased sweating;
  • Irritability and anxiety;
  • Involuntary trembling of hands or feet (tremor);
  • Irregular menstrual cycles;
  • Increased frequency of bowel movements;
  • Irregular sleep patterns;
  • Tiredness and fatigue;
  • Nodules (swellings) on the thyroid gland;
  • Skin redness and swelling;
  • Change of the hair quality (it typically becomes more brittle and starts to thin);
  • Thyroid cancer;
  • Thyrotoxic crisis.

In elderly patients, an overactive thyroid gland increases risk of dementia, systemic embolization, and stroke. 

What Are the Causes of Hyperthyroidism?

According to a study conducted by professor Lewis E. Braverman, Sun Y Lee, and Simone De Leo, hyperthyroidism may also be triggered by an autoimmune disease called  Graves’ ophthalmopathy, Plummer’s disease, thyrotoxicosis, excessive iodine intake from food, dietary supplements or medicines containing iodine, thyroid gland infection or tumor, pituitary gland tumor, etc.

Graves’ Ophthalmopathy

The thyroid-associated ophthalmopathy (TAO), or Graves’ ophthalmopathy, is a thyroid eye disease. When this medical condition occurs, the antibodies produced by the immune system of the affected individual overstimulate the thyroid gland. This results in excessive secretion of the T3 hormone in the bloodstream, thus affecting the immunological response of the body.

The typical physical manifestation of this autoimmune disease is bulging eyes, accompanied by most of the symptoms of hyperthyroidism. 

Plummer’s Disease

Plummer’s disease (also: toxic adenoma, or toxic multinodular goiter) is a medical condition where a single hyperfunctioning nodule of the thyroid gland produces excess thyroid hormone. In most cases, the overly stimulated nodule is an adenoma (a benign tumor). This disease is treated with radioactive iodine (131I) or surgery. 


When the bloodstream is oversaturated with increased (toxic) levels of thyroid hormone, the condition is labeled as thyrotoxicosis. This disease occurs as a complication of Graves’ Disease, Plummer’s disease, postpartum thyroiditis, overactivity in a multinodular goiter, as an inflammation of the thyroid gland, or an excessive secretion of the thyroid-stimulating hormone (TSH). 

Thyroid Cancer

Thyroid cancer is typically treated with radioactive iodine in order to destroy the targeted tumorous formation. Since the normal thyroid tissue accumulates iodine from the bloodstream, the malignant formations absorb excess amounts of the mineral. In such cases, radioactive iodine can be directed toward the tumor without affecting the surrounding healthy tissue of the thyroid gland. 

We can distinguish five main types of thyroid cancer:

  • Papillary thyroid cancer is a tumorous form that occurs when firm lumps form on otherwise healthy thyroid tissue. 
  • Follicular thyroid cancer is the most aggressive and wide-spreading cancer form that can affect the thyroid gland, as it spreads through the bloodstream that reaches all other tissues and organs of the body. 
  • Medullary thyroid cancer attacks the type of cells located in the thyroid gland that are labeled as C-cells. These thyroid cells are responsible for the production of the hormone calcitonin. When these cells mutate into a tumor, they excrete a significant amount of calcitonin in the bloodstream, which is the first indicator of cellular change, i.e. a tumor marker. Since the C-cells are unable to absorb iodine, therapy with radioactive iodine is ineffective in the case of medullary thyroid cancer. 
  • Anaplastic thyroid cancer is also a form of highly aggressive cancer of the thyroid gland. It occurs in extreme cases of chronic iodine deficiency. The anaplastic thyroid cancer may spread to the trachea, esophagus, and lungs, thus inhibiting the normal respiratory process. 
  • A lymphoma is a form of cancer of the lymph nodes of the thyroid gland. It may occur in two variations: as a Hodgkin’s disease, and as a Non-Hodgkin’s disease. Chronic Hashimoto’s thyroiditis is the most frequent trigger of this form of thyroid cancer. 

What Is Iodine Deficiency?

The adequate level of iodine that is required for the normal functioning of the thyroid gland is 150 mcg of iodine per day for an adult person, and 200 mcg of iodine per day for pregnant women. The recommended daily allowance of iodine (RDAs) for lactating women is 290 mcg per day. When this mineral is ingested under the prescribed values, i.e. a person consumes very little iodine through food, iodine deficiency occurs. 

The potentially severe adverse effects of iodine deficiency on the health of infants are one of the reasons why The Institute of Medicine in Washington, DC encourages breastfeeding. 

If iodine values are lower than the normal level during pregnancy, the mother is at heightened risk of elevated blood pressure and other cardiovascular problems. At the same time, the baby may be born with mental retardation in addition to the vast list of potential disorders triggered by iodine deficiency. 

It’s especially significant for women who plan pregnancy, are pregnant, or are breastfeeding to make sure that their iodine intake is within the recommended quantities.,  Intake below the recommended value may lead to irregular development of the baby’s brain, autism, and even fetal hypothyroidism.

After birth, babies keep receiving an adequate intake of iodine through breast milk. Additionally, iodine deficiency can result in various birth defects, infertility, peripheral neuropathy, mental disorders, etc. These are some of the reasons why iodine deficiency is considered to be the most common preventable cause of mental retardation. 

In most countries across the world, iodine is added to table salt in order to prevent the diseases caused by the deficiency of this mineral in daily nutrition. 

Symptoms of Iodine Deficiency

Not having an adequate intake of iodine may lead to various adverse health conditions and symptoms, such as:

  • Weight gain;
  • Lack of energy;
  • Hormonal disbalance;
  • Cognitive problems;
  • Mood swings;
  • Depression;
  • Anxiety;
  • Slow metabolism and constipation;
  • Low immunological defense;
  • Emotional instability due to the hormonal disbalance;
  • Breast cysts (fibrocystic breast disease);
  • Breast tenderness during the menstrual cycle;
  • Failure of some organs of the body;
  • Dysfunctional thyroid gland;
  • Brittle hair and nails;
  • Hair loss;
  • Digestive problems;
  • Fatigue;
  • Pain in the muscles;
  • Swelling of the extremities.

Without a sufficient iodine supply, the thyroid glands would swell up. Severe iodine deficiency can lead to a medical condition that is referred to as goitre (or goiter), hypothyroidism, or mental retardation (especially in children). 


When the thyroid gland is underactive, it leads to a condition known as hypothyroidism. In other words, the levels of thyroxine secreted by the thyroid gland are insufficient in order to promote the health and function of the body’s tissues and organs that receive the hormone through the bloodstream.

What Are the Symptoms of Hypothyroidism?

Hypothyroidism may lead to a number of health disorders that display some of the following symptoms as side effects of the lack of iodine in the body:

  • Tiredness or fatigue;
  • Weight gain despite a healthy appetite;
  • Swelling of the face and the extremities (puffiness);
  • Weakness in the muscles;
  • Dryness of the skin;
  • Irregular bowel movements and constipation;
  • Elevated cholesterol levels in the blood;
  • Painful or stiff joints;
  • Irregular menstrual cycles;
  • Hormonal imbalance;
  • Brittle and fine hair;
  • Hair loss;
  • Excessive sleeping;
  • Slower pulse;
  • Cognitive problems;
  • Mental disorders;
  • Problems with memory;
  • Goiter (enlarged thyroid gland).

Hypothyroidism in Infants and Children in Development

In infants, very young children, and teenagers, lack of iodine in their daily nutrition may also lead to hypothyroidism with severe consequences, such as:

  • Mental retardation due to irregular brain development;
  • Delayed development of the bony structures of the body (bones and teeth);
  • Late puberty;
  • Growth problems and short stature;
  • Autoimmune diseases;
  • Feeding problems and difficulty swallowing.

Since their metabolism is unable to produce sufficient quantities of the thyroid gland hormones thyroxine (T4) and triiodothyronine (T3) due to lack of iodine in their molecular structure, the homeostasis, i.e. the balance of functions of the growing body of children becomes disturbed, so that the immunological response is immensely compromised.

According to a study conducted by Michael B. Zimmermann, MD at the Swiss Federal Institute of Technology, Zurich, iodine deficiency is the number one reason for a number of disorders with endangering consequences. 


If there isn’t enough iodine in the thyroid gland, the systems of the body whose function depends on thyroxine (T4) and triiodothyronine (T3) put a lot of stress on the most important gland of the endocrine system. This makes the thyroid gland dysfunctional, which further triggers other adverse medical conditions. One of them is the abnormal enlargement of the thyroid gland, known as goitre (or goiter). 

Goitre is the most common problem caused by a dysfunctional thyroid gland and inadequate levels of iodine. Namely, when the levels of iodine in the body drop below the adequate level, the thyroid gland tries to cage the remaining quantity of thyroxine by forming a ‘sack’. This swelling triggered by the lack of iodine in the thyroid gland is visible under the neck of the affected person. 

Types of Goitre

This medical condition can be manifested in several distinct forms:

  • Endemic goitre – Also known as colloid goitre, this form is triggered by a lack of iodine intake from nutrition. This goitre manifestation is a rare occurrence in the countries that add iodine in the table salt, such as the United States.
  • Simple goitre – A form that occurs when the thyroid gland is not capable of producing sufficient amounts of thyroxine hormone.
  • Multinodular goitre – When several nodules (lumps) appear on the thyroid gland as a result of its dysfunctionality, the medical condition is referred to as a multinodular goitre
  • Sporadic or nontoxic goitre – This form of goitre is mainly caused by the use of some medicines. After discontinuing the medical therapy that has triggered the condition, the sporadic goitre may subdue by itself. 

What Are the Symptoms of Goitre?

The person affected by any of the aforementioned forms of goitre typically experiences the following symptoms:

  • Coughing bouts;
  • Breathing difficulty;
  • Swallowing difficulty;
  • Vocal chord changes;
  • Hoarseness of the voice;
  • Feeling of tightness in the throat;
  • Swelling or protrusion of the veins located at the neck.

If this condition occurs as a result of hyperthyroidism, sweating, nausea, and shakiness are the main symptoms that accompany the disease. On the other hand, if the goitre is triggered by hypothyroidism, dryness of the skin, constipation, irregular circadian cycles, weight gain, and tiredness are the main symptoms experienced by the affected individual. 


Cretinism, or congenital iodine deficiency syndrome, is a severe disease that occurs when the iodine content absorbed in the thyroid gland is under the required level, especially in newborn children. Due to the inability of the thyroid gland to produce sufficient amounts of the vitally important hormones, the children born with severe forms of hypothyroidism suffer from mental retardation, stunted growth (dwarfism), impaired cognitive skills, and mental health, and underdeveloped neurological system of the brain. 

This medical condition usually results from a genetic defect, lack of iodine in the mother’s body during pregnancy, exposure of the mother to radioactive iodine during pregnancy, or a mother that has been administered therapy that blocks the production of the thyroid hormone during pregnancy.

What are the Symptoms of Cretinism?

Children affected by this congenital form of hypothyroidism typically display:

  • Goiter;
  • Dwarfism;
  • Delayed puberty;
  • Mental problems;
  • Autistic behavior;
  • Cognitive problems;
  • Memory impairment;
  • Impaired hearing and vision;
  • Abnormal movements of the extremities;
  • Irregular formation of the bones and teeth;
  • Problems with speaking or not speaking at all (mutism).

Hashimoto’s Thyroiditis

The term thyroiditis in the name of this autoimmune disorder refers to an inflammation of the thyroid gland. As a form of chronic lymphocytic thyroiditis, Hashimoto’s thyroiditis is one of the most frequently occurring diseases of the dysfunctional thyroid gland in the United States according to the American Thyroid Association

What are the Symptoms of Hashimoto’s Thyroiditis?

Hashimoto’s thyroiditis is considered to be a genetically inherited disease with symptoms that are not always immediately recognizable and related to this thyroid gland condition. They include:

  • Excessive tiredness;
  • Irregular bowel movement and constipation;
  • Weight gain;
  • Depression;
  • Cognitive problems;
  • Irregular menstrual periods;
  • Frequent mood swings;
  • Increased sensitivity to cold;
  • Dryness of the skin.

If this inflammation triggers swelling of the thyroid gland (goiter), it may also result in problems with swallowing, since the gland’s anatomical location is on the neck, right under the laryngeal prominence.

List of Iodine-Rich Food Sources

The health and normal functioning of the thyroid gland is of vital importance for the maintenance and the optimal functioning of the metabolism and the cellular mechanisms. This can be achieved by regulating the intake of dietary iodine. 

Iodine-rich nutrition is the best way of getting adequate levels of iodine into the body, which are required for maintenance of the proper thyroid gland function. Assorted foods that are rich in iodine include: 

  • Asparagus;
  • Bacon;
  • Beans;
  • Bread;
  • Beetroot;
  • Beet – leaves;
  • Bockwurst;
  • Butter;
  • Cabbage;
  • Carrots;
  • Cheese; 
  • Clams;
  • Cod;
  • Cowpea;
  • Crab;
  • Egg – boiled;
  • Fish stick;
  • Haddock;
  • Herring;
  • Kelp (a type of seaweed);
  • Lettuce;
  • Lobster;
  • Mackerel;
  • Milk; 
  • Oats;
  • Onion;
  • Oysters;
  • Peas;
  • Pork;
  • Potatoes;
  • Poultry;
  • Salmon;
  • Salt – Iodized;
  • Salt – Rock;
  • Sardines;
  • Seaweed; 
  • Shrimp;
  • Soya beans;
  • Squash;
  • Spinach;
  • Tomato;
  • Trout;
  • Tuna;
  • Turnips;
  • Turkey.

The recommended dietary intake of iodine has been regulated by the National Institutes of Health, Office of Dietary Supplements.  Please refer to the full list which also includes the dietary reference intakes of vitamin A, vitamin K, arsenic, boron, chromium, copper, iodine, iron, manganese, molybdenum, nickel, silicon, vanadium, and zinc

Who Is at Risk of Iodine Deficiency?

People who avoid dairy products and fish, which are natural sources of iodine, are classified as the group with the highest risk of diseases caused by a dysfunctional thyroid gland. Thus, people who don’t include iodine-rich foods in their nutrition due to an allergy, intolerance, or personal preference can avoid iodine deficiency by taking iodine supplements. 

However, people who suffer from an excess amount of iodine accumulated in the thyroid gland must avoid additional iodine intake via supplements.

Iodine Supplements

There are several forms of iodine supplements that are used to increase the iodine level in the thyroid gland. They are used to improve both the iodine status and the thyroid function regarding the support of the immune system, health of the neurological and cardiovascular system, and the metabolic processes. 

Mostly, the multivitamin/mineral supplements contain iodine in the form of potassium iodide or sodium iodide. Supplements that include this vitally important mineral for our body are usually taken in the following forms in order to avoid some specifically related health problems:

  • Potassium Iodide – This form blocks the absorption of the radioactive iodine in the thyroid gland after radiotherapy.
  • Potassium Iodate – This ionic chemical compound is used to iodize table salt in order to prevent iodine deficiency. It’s also used in some types of baby formula milk.
  • Nascent Iodine – Also known as a transformative nano-colloidal detoxified iodine, this supplemental form of iodine has a very similar chemical structure to the iodine form that is converted into thyroxine by the thyroid gland. Therefore, it’s easily absorbed and used up by the body’s tissues and organs which makes it the best form of iodine supplement. 
  • Lugol’s Solution Iodine – As the strongest iodine solution, this supplement is made up of 85% distilled water, 10 percent potassium iodide, and 5 percent elemental iodine. It’s used as an inhibitor of unwanted thyroid hormone secretion. 
  • Kelp – Dietary supplements of iodine-containing kelp are also available as an iodine supplement. Kelp is a bulky brown-colored seaweed from the botanic Laminariales. It’s considered to be a heterokont which refers to algae made up of several other seaweed types. Since it grows in nutrient-rich saltwater, kelp is rich in iodine and other minerals,  vitamins, and antioxidants. This makes the seaweed a staple in Asian cuisine, often included in sushi, added to ice-cream, and found in salad dressings. The nutritional benefits of kelp can be utilized in a form of iodine supplementation or through raw consumption.                    

It’s important to ask for the advice of your healthcare provider prior to implementing any type of supplement to your nutrition. 

The Use of Iodine in Medicine

Iodine is used in the formation of a compound that is considered to be a universal medicine. It can be applied both inside and outside the body (counterirritant). 

The first iodoform solution (an organic compound of iodine) was prepared in 1822, by conducting electrolysis of aqueous solutions made up of acetone, inorganic iodides, and sodium carbonate.

Several decades later, the antiseptic properties of this strong iodine compound were determined, which placed iodoform on the list of the most helpful medicinal solutions. This iodine compound is used for the disinfection of minor skin wounds and cuts, as well as for the disinfection of larger physical surfaces, such as hospital floors. 

Povidone-Iodine (PVP-I) (C6H9NO)n·xI

Povidone-iodine, or iodopovidone, is considered to be one of the essential medicines by the World Health Organization (WHO). After evaluating the scientific evidence of the medical and cost-effective features of povidone-iodine, the WHO’s Expert Committee listed the 10% iodine solution (equivalent to 1% available iodine)among medicines with antiseptic properties that have effective, safe, and affordable application in the basic health-care system. As a strong antiseptic, povidone-iodine acts as a strong inhibitor of the growth of the infectious microorganisms and prevents their spreading. 

Iodine -131 (Radioiodine) 

The most frequently used medical modality in the treatment of hyperthyroidism is the X-ray irradiation of the thyroid gland by the 131I isotope. This form of iodine is also used in the medical treatment of fibrocystic breast disease, breast pain (mastalgia), and radiation emergencies, so as to protect the thyroid gland from radioactive iodides.

Iodine in Everyday Life

The uses of iodine in everyday life are versatile and plentiful. Not only is this mineral one of the essential nutrients for the human body, but its elemental form and compounds are also considered to be essential in medicine. 

  • Iodine and iodine compounds have wide application in healthcare settings and households as antiseptic solutions that destroy bacteria or germs. They’re used to clean a wound prior to dressing application, to relieve pain after an open injury, and included in dental mouthwash solutions. These solutions are also used for the disinfection of larger surfaces.
  • The radiopacity of iodoform makes this iodine compound a vital chemical ingredient in dental paste and root canal filling materials. When it comes into contact with secretions or endodontic infections, iodoform decomposes. In this way, it releases iodine from the dental materials as an antiseptic component.
  • Organoiodine compounds such as iodoform (CHI3), methylene iodide (CH2I2), and methyl iodide (CH3I) are typically used as disinfectants and pesticides.
  • Iodine is an added nutrient in some food products, such as table salt. In many countries, table salt is fortified with iodine by law in order to prevent thyroid diseases caused by lack of iodine in nutrition. Iodine fortification is highly important in the nutrition of school children so that they may receive the recommended dietary allowance of this mineral. 
  • The pure, elemental form of iodine is used in the industrial production of acetic acid and some polymers.
  • Because the heavy iodine nucleus has an excellent absorbing power over -rays, polyiodoorganic compounds have a wide application as X-ray contrasting agents in fluoroscopy (a type of medical imaging).
  • Organoiodine lubricants are used in the machine, turbines, and spacecraft industries, as well as titanium and stainless steel production.

How Dangerous Is Iodine?

Despite being labeled as one of the most useful chemicals in medicine, iodine and iodine preparations can trigger some toxic reactions. The adverse reaction to this poisonous halogen is stronger upon exposure to larger and stronger concentrations of iodine compounds.

The pure, elemental form of iodine is not only highly toxic, but it may also be lethal. On the other hand, iodines are not considered to have a toxic effect, but they can still have a negative impact on the function of the thyroid gland. 

In cases of a toxic reaction to the pure elemental form of iodine or its compounds, the affected individual may experience the following adverse symptoms or health conditions:

  • Delirium;
  • Excitation; 
  • Depression;
  • Lack of appetite;
  • Strong headaches;
  • Anaphylactic shock;
  • Tiredness and fatigue;
  • Irregular heartbeat (tachycardia);
  • A strong and persistent iodoform taste;
  • Excessive constriction of the pupil (miosis).

Environmental Effects of Iodine

The chemical element iodine naturally occurs in water bodies. This is largely due to the highly concentrated presence of tri-iodine thyroxine in seaweed, corals, shellfish, sea sponges, and fish. That’s why saltwater has a higher iodine saturation than rivers. 

The iodine may evaporate from the waters into the air in a form of iodine gas. Both as a water solute or a gas, iodine imposes a low environmental risk as it’s already found in almost all life forms. 

The reaction of iodine and water can be seen from the following formula:

I2(l) + H2O(l)- > OI-(aq) + 2H+(aq) + I-(aq)

Since iodine possesses strong antiseptic and antibacterial properties, it’s used as a disinfection medium for the purification of drinking water. 

On the Effects of Radioactive Iodine After the Chernobyl Nuclear Explosion

131I is the iodine form that is largely responsible for the radioactive contamination of the environment. Iodine-131 is the isotope of iodine most frequently found in the nuclear radioactive waste where nuclear incidents happen or nuclear testings are performed. 

The World Health Organisation (WHO) has also reported the hazardous effects of radioactive iodine after the Chernobyl nuclear explosion. Namely, after the worst nuclear catastrophe in the history of humankind occurred in Chernobyl in 1986, an enormous amount of radioactive material was released into the atmosphere. The radioactive particles emitted after the explosion of the nuclear reactor 4 covered a vast territory encompassing several countries. It left horrific health consequences to the people who had been exposed to the radiation. 

Thyroid cancers occurring without any prior triggers and leukemia were the most frequent adverse health effects of the radiation recorded among the affected individuals. The scientific assessments of the radioactive debris derived evidence of radioiodine as one of the major contaminants and the reason behind the thyroid-related diseases and deaths that started occurring after the blast of the nuclear reactor, especially in contaminated areas.

The people who had consumed food contaminated with radioactive iodine released by the nuclear catastrophe were the ones whose thyroid glands were affected the most. They had the highest concentration of radioactive iodine in the thyroxine producing gland. 

Isotopes of Iodine

Iodine is a monoisotopic element because it has only one stable isotope among the 37 forms of the chemical element. The 127I is not only the single, stable, and nonradioactive iodine isotope, but it’s also the most abundant naturally occurring form of iodine. 

The other 36 forms of iodine undergo radioactive decay. The iodine-129 stands out from the group of iodine isotopes with the longest half-life of 15.7 million years. What’s interesting about this radioactive isotope is that iodine-129 is obtained as a byproduct of nuclear fission accidents or nuclear tests.

With a half-life of less than 60 days, the iodine isotopes 123I, 124I, 125I, and 131I have been widely used in the field of medicine as tracers and therapeutic agents in radiography. These four radionuclides are also the most exploited forms of iodine. 

With a half-life of less than seven hours, the 135I isotope of iodine is the shortest living form of this chemical element. However, since it undergoes a decay into the most powerful neutron absorber 135Xe, this iodine form is obtained as a byproduct of the fissions triggered within nuclear reactors. 


[n 1]

ZNIsotopic mass (Da)

[n 2][n 3]


[n 4]



[n 5]



[n 6][n 7]

Spin and


[n 8][n 4]

Natural abundance (mole fraction)
Excitation energy[n 4]Normal proportionRange of variation
108I5355107.94348(39)#36(6) msα (90%)104Sb(1)#  
β+ (9%)108Te
p (1%)107Te
109I5356108.93815(11)103(5) µsp (99.5%)108Te(5/2+)  
α (.5%)105Sb
110I5357109.93524(33)#650(20) msβ+ (70.9%)110Te1+#  
α (17%)106Sb
β+, p (11%)109Sb
β+, α (1.09%)106Sn
111I5358110.93028(32)#2.5(2) sβ+ (99.92%)111Te(5/2+)#  
α (.088%)107Sb
112I5359111.92797(23)#3.42(11) sβ+ (99.01%)112Te   
β+, p (.88%)111Sb
β+, α (.104%)108Sn
α (.0012%)108Sb
113I5360112.92364(6)6.6(2) sβ+ (100%)113Te5/2+#  
α (3.3×10−7%)109Sb
β+, α109Sn
114I5361113.92185(32)#2.1(2) sβ+114Te1+  
β+, p (rare)113Sb
115I5362114.91805(3)1.3(2) minβ+115Te(5/2+)#  
116I5363115.91681(10)2.91(15) sβ+116Te1+  
117I5364116.91365(3)2.22(4) minβ+117Te(5/2)+  
118I5365117.913074(21)13.7(5) minβ+118Te2−  
119I5366118.91007(3)19.1(4) minβ+119Te5/2+  
120I5367119.910048(19)81.6(2) minβ+120Te2−  
121I5368120.907367(11)2.12(1) hβ+121Te5/2+  
122I5369121.907589(6)3.63(6) minβ+122Te1+  
123I[n 9]5370122.905589(4)13.2235(19) hEC123Te5/2+  
124I[n 9]5371123.9062099(25)4.1760(3) dβ+124Te2−  
125I[n 9]5372124.9046302(16)59.400(10) dEC125Te5/2+  
126I5373125.905624(4)12.93(5) dβ+ (56.3%)126Te2−  
β (43.7%)126Xe
127I[n 10]5374126.904473(4)Stable[n 11]5/2+1.0000 
128I5375127.905809(4)24.99(2) minβ (93.1%)128Xe1+  
β+ (6.9%)128Te
129I[n 10][n 12]5376128.904988(3)1.57(4)×107 yβ129Xe7/2+Trace[n 13] 
130I5377129.906674(3)12.36(1) hβ130Xe5+  
131I[n 10][n 9]5378130.9061246(12)8.02070(11) dβ131Xe7/2+  
132I5379131.907997(6)2.295(13) hβ132Xe4+  
133I5380132.907797(5)20.8(1) hβ133Xe7/2+  
134I5381133.909744(9)52.5(2) minβ134Xe(4)+  
135I[n 14]5382134.910048(8)6.57(2) hβ135Xe7/2+  
136I5383135.91465(5)83.4(10) sβ136Xe(1−)  
137I5384136.917871(30)24.13(12) sβ (92.86%)137Xe(7/2+)  
β, n (7.14%)136Xe
138I5385137.92235(9)6.23(3) sβ (94.54%)138Xe(2−)  
β, n (5.46%)137Xe
139I5386138.92610(3)2.282(10) sβ (90%)139Xe7/2+#  
β, n (10%)138Xe
140I5387139.93100(21)#860(40) msβ (90.7%)140Xe(3)(−#)  
β, n (9.3%)139Xe
141I5388140.93503(21)#430(20) msβ (78%)141Xe7/2+#  
β, n (22%)140Xe
142I5389141.94018(43)#~200 msβ (75%)142Xe2−#  
β, n (25%)141Xe
143I5390142.94456(43)#100# ms [> 300 ns]β143Xe7/2+#  
144I5391143.94999(54)#50# ms [> 300 ns]β144Xe1−#  

Source: Wikipedia

List of Iodine Compounds 

Iodine is the least reactive of all halogen elements, despite its high reactivity. It occurs in the form of I2 molecules, as iodine ions, or as a salt of iodic acid with IO3-anion (i.e. iodates). In the chemical reactions with other chemicals, iodine mostly forms iodo-complexes, iodides, alkali metal iodides, and oxyhalides. 

Element 53 easily makes chemical reactions with both phosphorus and hydrogen, but it’s very reactive with carbon or oxygen. When iodine is combined with ammonia, it produces nitrogen triiodide (NI3) – an inorganic touch-sensitive compound that explodes even at the slightest contact with alpha radiation. The loud detonation of nitrogen triiodide releases a purple cloud of iodine vapor.  

The following is an extensive list of iodine compounds:

  • Aluminum iodide
  • Aluminum monoiodide
  • Americium(II) iodide
  • Antimony oxychloride
  • Astatine iodide
  • Beryllium iodide
  • Bis(pyridine)iodonium(I) tetrafluoroborate
  • Cadexomer iodine
  • Chromium(III) iodide
  • Cobalt(II) iodide
  • Copper(I) iodide
  • Cyanogen iodide
  • Cyclopentadienyliron dicarbonyl iodide
  • Eschenmoser’s salt
  • Ethylenediamine dihydroiodide
  • Hydrogen iodide
  • Hypoiodous acid
  • Iodic acid
  • Iodine azide
  • Iodine heptafluoride
  • Iodine monobromide
  • Iodine monochloride
  • Iodine monofluoride
  • Iodine nitrate
  • Iodine oxide
  • Iodine pentafluoride
  • Iodine pentoxide
  • Iodine tribromide
  • Iodine trichloride
  • Iodine trifluoride
  • Iodobenzene dichloride
  • Iodomethylzinc iodide
  • Iodophor
  • Iodous acid
  • Lead(II) iodide
  • Lithium iodide
  • Mendipite
  • Pentaiodide
  • Periodic acid
  • Potassium tetraiodomercurate(II)
  • Quinoline methiodide
  • Schuetze reagent
  • Tantalum(V) iodide
  • Telluride iodide
  • Tetraiodonickelate
  • Thyroid blocker
  • Trimethylplatinum iodide
  • Uranium(IV) iodide
  • Zinc iodide
  • Zirconium(IV) iodide

Organo-Iodine Compounds

The organic compounds that are made up of one or more carbon–iodine bonds are referred to as organo-iodine compounds. They rarely occur in nature, but there’s a large number of these iodide compounds in the realm of organic chemistry. 

All organo-iodine compounds contain an iodide that is bonded to one carbon center. Due to their structural formation, these compounds are classified as derivatives of I−. Iodoform (CHI3), methylene iodide (CH2I2), and methyl iodide (CH3I) are the organo-iodine compounds with the broadest practical application. 

Iodoform (CHI3)

Remember the smell of hospital halls? That’s the iodoform, a strong iodoalkane compound. Also known under the name triiodomethane, this pale yellow and slightly oily crystalline substance has been used for a long time as an external disinfectant and wound dressing for skin due to its strong antiseptic and antimicrobial properties. 

Thyroxine Hormones

The hormones of the thyroid gland thyroxine (T4) and triiodothyronine (T3) are organo-iodine compounds that are of vital importance for human health and homeostasis, i.e. the stability and equilibrium of the physiological processes in the body. Since they contain atoms of iodine in their structure as one of its main elements, the iodization of salt is government-mandated.


Iodoarenes are monocyclic or polycyclic aromatic hydrocarbon iodo-derivatives. These organic compounds typically have the role of agonists for specific brain receptors. For instance, the 25I-NBOMe (2C-I-NBOMe), Cimbi-5 iodo-compound is a synthetic hallucinogen that has a significant application in biochemical research that’s aimed at mapping out the brain’s usage of type 2A serotonin receptors. This particular iodo-derivative, as well as numerous other similar organic compounds of iodine, are widely used in radiology as radiotracers for positron emission tomography (PET) scans. 

The following is an extensive list of these organic compounds of iodine (iodoarenes) that have a significant place in radiology, as well as in biochemical research:

  • 2C-I
  • 5-I-R91150
  • 25I-NB34MD
  • 25I-NBF
  • 25I-NBMD
  • 25I-NBOH
  • 25I-NBOMe
  • Acetrizoic acid
  • Adipiodone
  • AGH-107
  • AGH-192
  • AH-494
  • AM-251 (drug)
  • AM-630
  • AM-679 (cannabinoid)
  • AM-694
  • AM-1241
  • AM-2233
  • Amiodarone
  • Benziodarone
  • Budiodarone
  • Calicheamicin
  • Chiniofon
  • Clioquinol
  • Cobimetinib
  • Diatrizoate
  • Diiodohydroxyquinoline
  • 2,5-Dimethoxy-4-iodoamphetamine
  • Diodone
  • Erythrosine
  • Flubendiamide
  • Hexaiodobenzene
  • Idoxifene
  • Iniparib
  • Iobenguane
  • Iobenzamic acid
  • Iobitridol
  • Iocarmic acid
  • Iocetamic acid
  • Iodamide
  • Iodixanol
  • 4-Iodo-N, N-dimethylaniline
  • Para-Iodoamphetamine
  • Iodobenzamide
  • Iodobenzene
  • 2-Iodobenzoic acid
  • Iodocyanopindolol
  • Ortho-Iodohippuric acid
  • 1-Iodomorphine
  • Iodophenol
  • Iodophenpropit
  • 4-Iodopropofol
  • 5-Iodowillardiine
  • Iodoxamic acid
  • Iofendylate
  • Iofetamine (123I)
  • Ioflupane (123I)
  • Ioglicic acid
  • Ioglycamic acid
  • Iohexol
  • Iomazenil
  • Iomeprol
  • Iopamidol
  • Iopanoic acid
  • Iopentol
  • Iopromide
  • Iopydol
  • Iotalamic acid
  • Iotrolan
  • Iotroxic acid
  • Ioversol
  • Ioxaglic acid
  • Ioxilan
  • Ioxitalamic acid
  • Ipodate sodium
  • Metrizamide
  • Metrizoic acid
  • Nitroxynil
  • Propyliodone
  • Rafoxanide
  • Rose bengal
  • RTI-55
  • RTI-121
  • RTI-229
  • RTI-353
  • SB-258585
  • Sodium acetrizoate
  • Tetraiodobenzenes
  • Tiratricol
  • Trametinib
  • Tyropanoic acid

5 Interesting Facts and Explanations

  1. After being recognized as the discoverer of iodine, Bernard Courtois continued with the production of iodine and iodine salts.  In 1831, L’Académie Royale des Sciences, i.e. the Royal Academy of Sciences awarded him the Montyon Prize and 6,000 francs as a reward for his monumental discovery of a chemical element with exceptional medicinal value. Unfortunately, he failed to obtain a certificate of the invention for the discovery which left his family in poverty, despite his great contribution to the world of science. 
  2. For more than 50 years it was believed that Sir Humphry Davy was the discoverer of the chemical element iodine because he was the last chemist to support the scientific evidence derived from the research conducted by Courtois, Desormes, and Clément. Due to this misunderstanding, Sir Davy had to submit a letter of explanation to the Royal Institution in London that he was mistakenly assumed as the discoverer of element 53. After this, Courtois was rightfully recognized as the discoverer of iodine (I).
  3. Armand Séguin (1765-1835) is a French chemist who, in collaboration with his colleagues, succeeded in discovering morphium (with Bernard Courtois), determined the composition of the molecule of water (with Nicolas-Louis Vauquelin), and pioneered the studies on the function of the human metabolism (with Antoine Laurent Lavoisier). Additionally, by performing individual chemical experiments, Séguin discovered the method of tanning leather which brought him significant fortune. 
  4. The people who live in countries where the soil contains very little iodine are in greater need of iodine nutrition. New Zealand and countries in  South Asia, Southeast Asia, and Europe are considered to be on that list. 
  5. Low iodine concentrations in the breast milk of lactating mothers that can lead to hypothyroidism in their children can be assigned to the unhealthy habit of smoking.