Iodine (I)


Iodine is an element (atomic number 53) that is required by humans for the synthesis of thyroid hormones (triiodothyronine and thyroxine, or T3 and T4, respectively).
Chronic iodine deficiency can lead to numerous health problems in children and adults, including thyroid gland dysfunction (including goiter) and various neurologic, gastrointestinal, and skin abnormalities. Iodine deficiency in pregnant or nursing mothers can lead to significant neurocognitive deficits in their infants. "Cretinism," or severe mental retardation, is a rare outcome of severe iodine deficiency during early development. Growth stunting, apathy, impaired movement, or speech or hearing problems may occur. Many individuals living in developing countries may be at risk of iodine deficiency and its complications, and iodine deficiency is considered to be a preventable cause of mental retardation.
Iodine deficiency is rare in industrialized countries such as the United States, due to the enrichment of table salt and cattle feed with iodine. But deficiency is common in developing countries, where a supplementation program may be considered useful.
Humans obtain iodine from their diets. The amount of iodine in food or water depends upon the amount of iodine in the local soil. Areas with mountainous (glacier) water or heavy rainfall tend to be low in iodine content, increasing the risk of iodine deficiency.
Iodine has antimicrobial properties and is commonly used as a topical antiseptic.
This review does not discuss medical uses of radioactive iodine or iodine contrast agents for imaging studies such as computerized tomography (CT scanning).

Related Terms

Atomic number 53, Betadine®, cadexomer iodine, I, Iodin, iodine-125, iodine-131, iodized poppy seed oil, iodized salt, iodothyronine, iodotyrosine, KI, Licartin®, Lipiodol®, Lugol solution, Lugol's iodine, PI, polyvinylpyrrolidone-iodine, potassium iodide, povidone-iodine, PVP-I, radioiodine, SKI, strong iodine, tincture of iodine.
Note: This review does not discuss the medical uses of radioactive iodine or iodine contrast agents for imaging studies such as computerized tomography (CT scanning).

evidence table

These uses have been tested in humans or animals. Safety and effectiveness have not always been proven. Some of these conditions are potentially serious, and should be evaluated by a qualified healthcare provider.
Antimicrobial (Grade: A)
Iodine is commonly used in topical disinfectant preparations for cleaning wounds, sterilizing skin before surgical or invasive procedures, or sterilizing catheter entry sites. Betadine® solution, for example, contains povidone-iodine. Other topical disinfectants include alcohol and antibiotics, and iodine is sometimes used in combination with these. Iodine is also used as a surgical hand scrub and to disinfect medical equipment. Commercially prepared iodine products are recommended in order to assure appropriate concentrations. Iodine can be used as an antimicrobial agent for the emergency purification of water. Tablets and solutions are available. Effects generally occur within 15 minutes.
Goiter prevention (Grade: A)
Iodine deficiency is one of the causes of goiter (hypertrophy of the thyroid gland as it tries to make more thyroid hormone in the absence of iodine). Physically, goiter appears as an abnormal enlargement of the thyroid gland in the neck. Other causes of goiter include autoimmune thyroiditis, excess iodine, other hormonal disorders, radiation exposure, infectious causes, or inborn errors of metabolism. Although goiter due to low iodine intake is rare in developed countries, it may occur in regions with endemic low iodine levels. To avoid iodine deficiency in the United States, table salt is enriched with iodine ("iodized" salt), and iodine is added to cattle feed and used as a dough conditioner. Iodine supplementation is generally not recommended in developed countries where sufficient iodine intake is common. Excess iodine can actually cause medical complications (including goiter). Iodine supplementation should be considered in cases of known iodine deficiency and should be administered with medical supervision if possible. Notably, the treatment of goiter usually involves the administration of thyroid hormone, most commonly levothyroxine sodium (Synthroid®, Levoxyl®, Levothroid®). Iodine generally does not play a role in the acute management of this condition.
Iodine deficiency (Grade: A)
In regions with low iodine intake or cases of known deficiency, iodine enrichment of foods or supplementation should be considered. To avoid iodine deficiency in the United States, table salt is enriched with iodine ("iodized" salt), and iodine is added to cattle feed and used as a dough conditioner. While iodine deficiency is not common in developed countries, it is common in other parts of the world. When considering iodine enrichment or supplementation, supervision by medical personnel or public health officials is recommended, due to the potential complications involved with iodine replacement after previous deprivation, particularly if considering supplementation in pregnant women or children.
Radiation emergency (potassium iodide thyroid protection) (Grade: A)
Iodine-131 is a component of nuclear fallout and is dangerous because the thyroid gland concentrates ingested iodine. Nonradioactive potassium iodide (KI) tablets may be taken by individuals at risk for radiation exposure in order to reduce levels of radioactive iodine uptake by the thyroid, thus reducing the risk of later development of thyroid cancer. It is important to note that KI does not provide immediate protection from radiation damage and does not have protective effects against other complications of radiation exposure. KI can serve as a part of a general strategy in cases of radiation emergencies, in conjunction with shelter and control of foodstuffs. Many radiation emergency kits include KI.
Cognitive function (iodine-deficient children) (Grade: B)
Iodine is required for the production of thyroid hormones, which are necessary for normal brain development and cognition. In children, prolonged iodine deficiency leads to learning disabilities, a lower intelligence quotient (IQ), and poor motivation to achieve. There is evidence that iodine supplementation improves perceptual reasoning, information processing, fine motor skills, and visual problem solving in iodine-deficient children. For this reason, it is important for pregnant and lactating women, as well as children, to have sufficient iodine intake.
Conjunctivitis (Grade: B)
Povidone-iodine solutions have been used in the management of childhood bacterial conjunctivitis (pinkeye) and may be as effective as other antibacterial solutions such as neomycin-polymyxin B-gramicidin. A combination of povidone-iodine and dexamethasone has been used to treat adenoviral conjunctivitis. It turns the surface of the eye brown for a few minutes. Medical supervision is advised.
Fibrocystic breast disease (Grade: B)
Fibrocystic breast disease is a benign form of iodine deficiency characterized by lumpy, painful breasts and palpable fibrosis. Iodine supplementation has reduced pain and other symptoms associated with this condition.
Graves' disease (adjunct iodine/iodides) (Grade: B)
Graves' disease is an immune-mediated disorder that causes hyperthyroidism. Thyroid-stimulating immunoglobulins bind to the thyroid-stimulating hormone (TSH) receptor, mimic the action of thyroid TSH, and stimulate thyroid growth and thyroid hormone overproduction. Standard treatments for Graves' disease target the thyroid gland (rather than the source of the disorder) and include antithyroid drugs (such as propylthiouracil or methimazole), radioactive iodine to ablate (destroy) thyroid cells, or surgery to remove thyroid tissue. Beta-blocker drugs may be used to control symptoms. Iodide preparations can be used to suppress thyroid hormone release from the thyroid, such as strong iodine solution (Lugol solution), saturated solution of potassium iodide (SSKI), and iodinated radiographic contrast agents (sodium ipodate). Patients undergoing thyroid surgery are commonly treated preoperatively with antithyroid drugs to achieve a euthyroid (normal) state, then with SSKI.
Hearing loss (iodine deficiency) (Grade: B)
Auditory disturbances may be present in iodine-deficient children. Continuous iodine supplementation may improve the auditory thresholds.
Ocular surgery infection prevention / cataract surgery antisepsis (Grade: B)
Topical iodine solutions, such as povidone-iodine, are used preoperatively for sterilization prior to ophthalmologic procedures. For example, povidone-iodine solution has been studied and used as an antiseptic before cataract surgery.
Ophthalmia neonatorum prevention (Grade: B)
Ophthalmia neonatorum is conjunctivitis with eye discharge that occurs during the first month of life. Various bacteria can cause this condition, including
Periodontitis / gingivitis (Grade: B)
Povidone-iodine mouthwash has been suggested to reduce mouth flora from periodontitis or around oral surgery. There is evidence that the use of povidone-iodine during scaling and root planning (deep cleaning performed by a dentist or dental hygienist) reduces the depth of gum pockets where cavities may form.
Postcesarean endometritis (Grade: B)
Post-Cesarean endometritis occurs when uterine tissue starts to grow at the incision site following a Cesarean section. Preoperative vaginal scrub with povidone-iodine solution immediately before Cesarean delivery reduces the risk of postoperative endometritis, especially for women undergoing Cesarean delivery with ruptured membranes. This intervention does not seem to decrease the overall risk of postoperative fever or wound infection.
Thyrotoxicosis / thyroid storm (adjunct iodides) (Grade: B)
Hyperthyroid crisis (thyroid storm) is a medical emergency caused by excessive release of thyroid hormones into the circulation. Initial management of this condition involves inhibition of thyroid function with thioamide drugs such as propylthiouracil or methimazole. Iodides (such as potassium iodide) can then be administered to block the release of thyroid hormone, but they should only be given an hour after thioamides to assure that the iodide is not used by the thyroid to make more thyroid hormone and worsen symptoms. Caution is warranted, because iodide preparations carry a risk of causing serum sickness. Iodides should not be used for long-term treatment of thyrotoxicosis.
Bladder irrigation (Grade: C)
Povidone-iodine bladder irrigation has been suggested prior to catheter removal, or prior to prostatectomy surgery, to reduce the risk of infection. Research in this area is limited.
Bleeding (Grade: C)
Early research suggests that povidone-iodine may control bleeding during dental surgery better than saline. Additional research is needed before a conclusion can be made.
Bowel irrigation (Grade: C)
Povidone-iodine irrigation before large bowel resection has been suggested as a sterilization technique. Further study is warranted.
Cancer (Grade: C)
The potential role of nonradioactive iodine in cancer care remains unknown. Antioxidant and antitumor effects have been proposed, based on laboratory research. In contrast, some scientists have asserted that tumors may uptake more iodine than normal tissues. It has been suggested that high rates of gastric (stomach) cancer or low rates of breast cancer in coastal Japan may be due to high iodine intake, although this has not been demonstrated scientifically. Povidone-iodine solutions have been used as a part of alternative cancer regimens, such as the Hoxsey formula. Preliminary research has also indicated povidone-iodine solution as a potential rectal washout for rectal cancer. Iodine use has been linked to a decrease in prostate and stomach cancers in some populations. Overall, no clear conclusion can be drawn based on the currently available evidence.
Corpus vitreous degeneration (Grade: C)
Topical administration of iodine eye drops may reduce corpus vitreous degeneration. Further research is needed to confirm these results.
Dental caries (Grade: C)
In patients with early childhood caries, povidone-iodine treatment reduced the risk of further cavities developing. Further studies in this area are warranted.
Goiter treatment (Grade: C)
Iodine deficiency can cause goiter (hypertrophy of the thyroid gland). Other causes of goiter should be considered in patients with this condition, such as autoimmune thyroiditis, excess iodine, other hormonal disorders, radiation exposure, infectious causes, or inborn errors of metabolism. Although goiter due to low iodine intake is rare in developed countries, it may occur in regions with endemic low iodine levels. Initial management of goiter should involve a medical evaluation to identify the underlying cause and assessment of levels of thyroid hormones in the body. Treatment usually involves the administration of thyroid hormone, most commonly levothyroxine sodium (Synthroid®, Levoxyl®, Levothroid®). Iodine plays a role in goiter prevention, but not in acute management of this condition. Iodine deficiency should be corrected with iodine supplementation, if found.
Kashin-Beck osteoarthropathy (Grade: C)
Kashin-Beck disease is an osteoarthropathy found in selenium- and iodine-deficient areas. Iodine supplementation may be effective in the prevention and treatment of this condition. Further research in this area is needed.
Kidney problems (kidney cysts) (Grade: C)
Iodine has been suggested as a possible treatment for kidney cysts, which are small, fluid-filled sacs in the kidneys. There is conflicting evidence in this area. Further research is needed.
Lymphedema (filarial) (Grade: C)
Footcare with Betadine® may help in the management of filarial lymphedema. More research is needed in this area.
Molluscum contagiosum (Grade: C)
Molluscum contagiosum is a common skin infection that is caused by a pox virus. Povidone-iodine has been suggested as a topical treatment for molluscum. Research in this area is limited.
Mucositis from cancer treatment (mouth ulcers/irritation) (Grade: C)
There is limited research to suggest that iodine mouth rinses may decrease the severity of mucositis in the mouth related to cancer chemotherapy or radiation therapy. The management of mucositis should be discussed with the patient's cancer care team.
Oral intubation (Grade: C)
Limited evidence shows that gargling with povidone-iodine before oral intubation (opening airways with a tube) reduces the transport of bacteria into the trachea. More research is needed in this area.
Pelvic infection (Grade: C)
Vaginal douching with aqueous povidone-iodine followed by normal saline irrigation immediately before egg cell retrieval seems effective in preventing pelvic infection, without compromising the outcome of
Pneumonia (Grade: C)
There is limited evidence that regular oropharyngeal (in the mouth and pharynx) application of povidone-iodine may decrease the prevalence of ventilator-associated pneumonia in patients with severe head trauma. Evidence in this area is not conclusive at this time.
Renal pelvic instillation sclerotherapy (RPIS) (Grade: C)
There is limited evidence that povidone-iodine is as effective as 1% silver nitrate for RPIS. More research is needed in this area.
Septicemia (serious bacterial infections in the blood) (Grade: C)
Rinsing with povidone-iodine before dental procedures may help reduce the incidence and severity of bacterial infections of the blood. More research is needed in this area.
Thyroid disease (Grade: C)
Routine iodine supplementation may be useful for preventing recurrent nodular thyroid disease in patients from iodine-deficient regions. More research is needed in this area.
Visual outcomes in corneal ulceration (Grade: C)
Antibiotic therapy with povidone-iodine does not seem to improve visual outcomes in corneal ulceration. The effects of povidone-iodine alone are not clear.
Wound healing (Grade: C)
It is not clear if healing of wounds or skin ulcers is improved with the application of topical iodine solutions. Iodine solutions may assist with sterilization as a part of a larger approach to the healing process. Further research in this area is needed.
Premature infants (Grade: D)
Iodine is essential for the production of thyroid hormones, which are needed for brain development in newborns. Preterm infants often have low levels of iodine and thyroid hormones in the first few weeks after birth. Infant formula and human breast milk contain insufficient iodine to meet recommended intakes for preterm infants. However, there is limited evidence suggesting that dietary supplementation with iodine does not benefit preterm infants.