Fundamentals of Human Nutrition/Iodine
Iodine is an essential non-metallic mineral that can be found naturally, in trace amounts, within the body as well as several common foods such as kelp, shellfish, and probiotic yogurt. Upon consumption of foods containing iodine the digestive system breaks down these foods via gastrointestinal tract and iodine is readily absorbed into the body. Within the body iodine becomes the iodide ion (I-1) and bonds to a myriad of different organic compounds. Although the amount of iodide that can be found throughout the body is dwarfed by the amount of major minerals that can be found, it is still responsible for several major and minor roles within the body. In the body, approximately 70-80% of iodine is found in the thyroid gland while the other 20-30% is found primarily in the muscles, blood, and ovaries in women (University of Maryland Medical Center [UMMC], 2013). Iodide is required for thyroid hormone production, which is necessary for normal growth and development (Whitney & Rolfes, 2011). Iodine is important for everyone, but it is especially important for infants and pregnant women. Iodine deficiency can be detrimental to the health and growth of children and could lead to several complications both physically and mentally. In fact, Iodine deficiency is the most common cause of preventable mental impairment (UA 2015). Iodine deficiency is not a major problem in most prominent countries, due to farming techniques that promote iodine rich soils and popular usage of iodized salt. However, in several underdeveloped countries both women and children alike face the complications of iodine deficiency due to lack of access of iodine rich foods. Typically iodine can more easily be found in countries that have easy access to the ocean or countries that have settlements that have once been undersea. Therefore dryer and more inland countries such Ethiopia, Senegal and several others face the consistent problem of iodine deficiency (UA, 2015). Availability of iodine becomes scarce in countries with large and concentrated population as well, despite methods to combat iodine deifiency (AIIMS 2015).
Iodine is predominantly found in seafood and areas where the soil is rich in iodine such as coastal areas and land that was once under the ocean. Shellfish, white fish, seaweed, and plants grown in iodine-rich soil are excellent nutritional sources of iodine. Several countries are using iodized salt in place of standard cooking salts. These iodized salts can be used in several different meals to provide a sufficient amount of iodine in locations distant from the ocean. The use of iodized salts is highly popular, though it is recommended to get iodine from different sources as well. It is important to note that processed foods such as canned soups, which are especially common in American diets, do contain salt but it is almost never iodized salt (U.S. Department of Health & Human Services [HHS], 2011). Additional sources of iodine include bakery products, milk, and iodized salt- all of which are most common in developed countries (Whitney & Rolfes, 2011). Iodates or iodine salts are used as stabilizing agents in dough, which makes bakery products a source of iodine (UMMC, 2013). Dairies give medications including iodine to their livestock and use iodine to decontaminate equipment used for milking so products such as milk, yogurt, and butter are additional dietary sources for iodine consumption (Whitney & Rolfes, 2011). A method to disinfect drinking water with iodinated disinfection byproducts is being developed and gaining interest as well, and possibly a new source of iodine in one’s diet (SKLPCRR, 2015). Currently chloroamination of water is being more popularly used, however the demand for clean water and specifically iodine in certain countries could skew what the majority disinfection method is.
Iodine is necessary for normal thyroid function because it is a major component of the thyroid hormones known as T3 (triiodothryonine) and T4 (thyroxine). These two hormones are very significant in the body because they play a role in regulating the basal metabolic rate and body temperature. Additionally, these hormones are important for promoting growth, development, metabolism, and reproductive function. The thyroid hormones are also important for blood cell production and nerve and muscle function (Whitney & Rolfes, 2011). Iodine is also important in the health of mammary tissue (Ahad & Ganie, 2010 (Links to an external site). However, the thyroid gland needs no more than 70 micrograms per day to synthesize the requisite daily amounts of T4 and T3. The higher recommended daily allowance levels of iodine seem necessary for optimal function of a number of other body systems, including lactating breasts, gastric mucosa, salivary glands, oral mucosa, arterial walls, thymus, epidermis, choroid plexus and cerebrospinal fluid, among others.
The amount of iodine required each day depends on age. Below is a table that shows average daily-recommended amounts (HHS, 2011).
Life Stage (Recommended Amount)
- Birth to 6 months (110 mcg)
- Infants 7–12 months (130 mcg)
- Children 1–8 years (90 mcg)
- Children 9–13 years (120 mcg)
- Teens 14–18 years (150 mcg)
- Adults (150 mcg)
- Pregnant teens and women (220 mcg)
- Breastfeeding teens and women (290 mcg)
There are also restrictions regarding the maximum amount of iodine that should be consumed each day. These are known as Tolerable Uptake Intake Levels (UL) and they are the highest levels of iodine that can be consumed without causing side effects. These levels are documented below (UMMC, 2013).
Life Stage (Tolerable Uptake Intake Level (UL))
- Children 1–3 years (200 mcg)
- Children 4–8 years (300 mcg)
- Children 9–13 years (600 mcg)
- Teens 14–18 years (including pregnant & breastfeeding) (900 mcg)
- Adults 19 years and up (including pregnant & breastfeeding) (1100 mcg)
Iodine deficiency is an important health problem throughout much of the world, especially in underdeveloped countries and mountainous regions such as the Himalayas, Andes, and European Alps. Iodine deficiency is also a problem in river valley areas due to leaching of the iodine from the soil (Caballero, 2009). Iodine imbalance or deficiency is less common in developed countries such as the United States and Canada due to the iodization of salt. However, in parts of the world where iodine and iodized salt are not easily available, conditions known as goiter or cretinism can occur.
Goiter is one of the earliest signs of iodine deficiency. Goiter affects about 200 million people in the world and most cases are found in South America, Asia, and Africa. A goiter is a visible lump in the neck caused by an enlarged thyroid gland. The thyroid becomes enlarged due to the cells of the thyroid gland becoming enlarged in order to trap as much iodide as possible (Whitney & Rolfes, 2011). As the thyroid begins to enlarge, the pituitary gland begins secreting more TSH (thyroid stimulating hormone) in order to help the thyroid take in more iodide (Whitney & Rolfes, 2015). A goiter is described as being grade 1 if it can be felt but not seen when the neck is extended and it is described as being grade 2 if it can be seen when the neck is in a normal position (Institute of Medicine, 2001).
Cretinism is the mental and physical retardation of a person that is caused by iodine deficiency during pregnancy. This condition affects about six million people worldwide. Cretinism is irreversible, but can be prevented by the early identification and treatment of maternal iodine deficiency (Whitney & Rolfes, 2011). The World Health Organization recognizes iodine deficiency as the most common avoidable cause of brain damage today (Caballero, 2009).
An iodine deficiency also interferes with the synthesis of the thyroid hormones T3 and T4 because a major component of T3 and T4 is iodine. When there is a lack of iodine, there is an increased amount of TSH but a decreased amount of the two thyroid hormones – creating a greater imbalance in the body (Ahad & Ganie, 2010).
An overdose of iodine is not that common in the United States, as most foods that contain iodine do not contain enough to cause an individual to ingest an excess amount. Adults are advised not to ingest more than 1.1 mg/day, which is well above any recommended levels, to avoid an iodine overdose (Institute of Medicine, 2001). Symptoms of acute iodine poisoning are abdominal pain, shortness of breath, delirium, lack of urine, vomiting, and diarrhea (NLM, 2015). Even though goiters are associated with an iodine deficiency, an overdose of iodine can cause the thyroid to enlarge due to the elevated amounts of TSH (Institute of Medicine, 2001).
Pregnant women have to be exceptionally careful with their iodine intake. Iodine induced goiters have been found in newborns when the mother had an excess of iodine during pregnancy (Institute of Medicine, 2001 (Links to an external site.)). The iodine induced goiter in the fetus can suffocate and potentially kill the fetus (Whitney & Rolfes, 2015). If the mother has hyperthyroidism during pregnancy, the fetus is at risk of many complications such as growth retardation and a premature birth (Medscape, 1997). Studies have shown that children are more likely to have a lower IQ if their mother had high levels of TSH 16 weeks into the pregnancy (Zoeller, 2003).
There is also a correlation between breast cancer and an imbalance of iodine. However, there is not enough evidence to prove that either excess or a deficiency of iodine causes breast cancer (Smyth, 2003). Iodine has been found to be important in mammary tissue. An adequate amount of iodine in the mammary tissue helps prevent damage to the breast tissue while a deficiency of iodine in the mammary tissue is linked to damage of the breast tissue due to an accumulation of malondialdehyde (Ahad & Ganie, 2010 (Links to an external site.)).
References Caballero, B. (2009). Guide to nutritional supplements (pp. 227–235). Oxford, UK: Elsevier/Academic Press.
U.S. Department of Health & Human Services. (2011). Iodine. Retrieved August 3, 2015, from https://ods.od.nih.gov
University of Maryland Medical Center. (2013). Iodine. Retrieved July 28, 2015, from http://umm.edu
Whitney, E., & Rolfes, S. (2011). The Trace Minerals. In S. Gall & E. Feldman (Eds.),
Understanding nutrition (14th ed., pp. 418–419). Belmont, CA: Wadsworth.
University of the Azores. (2015). Iodine environmental availability and human intake in oceanic islands: Azores as a case-study. Azores, Portugal. Retrieved December 1, 2015, from http://www.ncbi.nlm.nih.gov/pubmed/
All India Institute of Medical Sciences. (2015). Prevalence of iodine deficiency among adult population residing in Rural Ballabgarh, district Faridabad, Haryana. New Delhi, India. Retrieved December 1, 2015, from http://www.ncbi.nlm.nih.gov/pubmed/
State Key Laboratory of Pollution Control and Resource Reuse. (2015). Formation and occurrence of new polar iodinated disinfection byproducts in drinking water. Nanjing, China. Retrieved December 1, 2015, from http://www.ncbi.nlm.nih.gov/pubmed/
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Institute of Medicine (US) Panel on Micronutrients. (2001). Iodine - Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc - NCBI Bookshelf. Retrieved from http://www.ncbi.nlm.nih.gov/books/NBK222323/
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Whitney, E., & Rolfes, S. R. (2015). Understanding nutrition. Stamford, CT: Cengage Learning.
Zoeller, R. T. (2003). Transplacental thyroxine and fetal brain development. Journal of Clinical Investigation, 111(7), 954–957. http://doi.org/10.1172/JCI200318236