Fundamentals of Human Nutrition/Iodine
Iodine is an essential non-metallic mineral that becomes the iodide ion in the gastrointestinal tract. Iodide is found naturally in the body in trace amounts, so it must be consumed in foods or liquids for proper bodily function. Iodide is required for thyroid hormone production, which is necessary for normal growth and development (Whitney & Rolfes, 2011). 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). Iodine is important for everyone, but it is especially important for infants and pregnant women. Iodine deficiency is a health problem throughout the world, especially in underdeveloped countries.
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. 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). 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).
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).
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).
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).
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.