Table of Contents
Iodine (I) is a non-metallic element that the body needs in very small (trace) amounts in order to remain healthy. It can only be acquired through diet. Deficiencies of iodine are a serious health problem in some parts of the world.
Iodine is essential to the formation of the thyroid hormones triiodothyronine (T3) and thyroxine (T4). Thyroid hormones regulate many basic metabolic processes. Solutions containing iodine can be used on the skin as a disinfectant because iodine kills bacteria. It can also be used to purify water contaminated with bacteria. In medical settings, iodine is used in diagnostic radioisotope scanning and it has other industrial uses.
The thyroid gland is a located in the front of the neck just below the Adam’s apple. It is part of a complex, tightly-controlled feedback cycle that regulates basic aspects of metabolism, such as how fast the body burns calories, growth rate, and body temperature.
Under stimulation by thyroid stimulating hormone (TSH) produced by the pituitary gland, the thyroid produces two hormones, triiodothyronine (T3) and thyroxine (T4). The formation of one(Illustration by GGS Information Services/Thomson Gale.)
molecule of T3 requires three molecules of iodine, while formation of T4 requires four molecules of iodine. The body contains between 20 and 30 mg of iodine, 60% of which is stored in the thyroid. The remainder is found in the blood, muscles, and ovaries. Thyroid hormones are broken down in the liver and some of the iodine is recycled. The rest is lost to the body in urine.
Iodine is found in soil and in the ocean. The amount of iodine varies widely by location. In mountainous regions where heavy rain and snow cause erosion or in low-lying regions where regular flooding occurs, the soil is especially deficient in iodine. The mountains of the Himalayas, Andes, and Alps are all iodine-poor as is the Ganges river valley. The International Council for the Control of Iodine Deficiency Disorders (ICCIDD) estimates that 38% of the world’s population, or about 2.2 billion people, live in areas where they are unlikely to get enough iodine without supplementation.
Iodine deficiency disorders (IDDs) create serious health problem. In the early 1900s, iodine deficiency
was common in interior regions of the United States and Canada, as well as many other non-coastal regions of the world. In the 1920s, the United States began a voluntary program of adding iodine (in the form of potassium iodide) to salt. Salt was chosen because all races, cultures, and economic classes use it, its consumption is not seasonal, and it is inexpensive. Adding 77 mcg of iodine per gram of salt costs about $0.04 per year per person in the United States. About 50% of table salt sold in the United States contains iodine. It is labeled ‘iodized salt.’ All table salt sold in Canada is iodized. In most other countries iodine is added at lower concentrations ranging from 10–40 mcg/gram.
Normal iodine requirements
The United States Institute of Medicine (IOM) of the National Academy of Sciences has developed values called Dietary Reference Intakes (DRIs) for vitamins and minerals. The DRIs consist of three sets of numbers. The Recommended Dietary Allowance (RDA) defines the average daily amount of the nutrient needed to meet the health needs of 97–98% of the population. The Adequate Intake (AI) is an estimate set when there is not enough information to determine an RDA. The Tolerable Upper Intake Level (UL) is the average maximum amount that can be taken daily without risking negative side effects. The DRIs are calculated for children, adult men, adult women, pregnant women, and breastfeeding women.
The IOM has not set UL levels for iodine in children under one year old because of incomplete scientific information. RDAs for iodine are measured in micrograms (mcg). The following are the daily RDAs and IAs for iodine for healthy individuals. They are the same as the recommendations made by the World Health Organization (WHO).
- children birth-6 months: RDA 110 mcg; UL not available
- children 7-12 months: RDA 130 mcg; UL not available
- children 1-3 years: RDA 90 mcg; UL 200 mcg
- children 4-8 years: RDA 90 mcg: UL 300 mcg
- children 9-13 years: RDA 120 mcg; UL 600 mcg
- adolescents 14-18 years: RDA 150 mcg; UL 900 mcg
- adults 19 years and older: RDA 150 mcg; UL 1,100 mcg
- pregnant women under age 19: RDA 220 mcg; UL 900 mcg
- pregnant women age 19 and older: RDA 220 mcg; UL 1,100 mcg
- breastfeeding women under age 19: RDA 290 mcg; UL 900 mcg
- breastfeeding women age 19 and older: RDA 290 mcg; UL 1,100 mcg
Sources of iodine
Iodine must be acquired from diet. Marine plants and animals, such as cod, haddock, and kelp (seaweed), are an especially good source of iodine because they are able to concentrate the iodine found in sea-water. Freshwater fish are a less good source. Plants contain varying amounts of iodine depending on the soil in which they are grown.
In industrialized countries, feed for cattle, chickens, and other domestic animals is often fortified with iodine. Some of this iodine finds its way into animal products that humans eat— milk, eggs, and meat. In developing countries where feed is not enriched or cattle are raised on grass, these animal products do serve as a source of iodine.
Commercially processed foods are often made with iodized salt. The iodine content of salt changes very little during processing. Sometimes an iodine-containing stabilizer is added to commercial bread dough. This increases the iodine content of bread. The stabilizer is used less often now than it was in the twentieth century. However, for many people, commercially processed foods are their main source of iodine. Iodine is also found in most multivitamin tablets.
Iodine can be absorbed through the skin from iodine-based disinfectant solutions. Automobile exhaust puts some iodine into the air, and this can be absorbed through the lungs. Neither of these provide significant amounts of iodine for most people.
The following list gives the approximate iodine content for some common foods:
- kelp, 1/4 cup wet: 415 mcg or more. Amount is highly variable
- salt, iodized, 1 g: 77 mcg; 1 teaspoon: 400 mcg
- haddock, 3 ounces: 104-145 mcg
- cod, 3 ounces: 99 mcg
- shrimp, 3 ounces: 21-37 mcg
- processed fish sticks: 17 mcg per piece
- tuna, canned, 3 ounces: 17 mcg
- milk, 1 cup: 55-60 mcg
- cottage cheese, 1/2 cup: 25-75 mcg
- egg, 1 large: 18-29 mcg
- turkey breast, cooked, 3 ounces: 34 mcg
- ground beef, cooked, 3 ounces: 8 mcg
- seaweed, dried, 1 ounce: up to 18,000 mcg
Because of iodine supplementation, iodine deficiency is not a serious health problem in most industrialized countries, but it is in many developing countries. Internationally, about 2.2 billion people are at risk for IDDs. Women who do not get enough iodine have higher rates of infertility, miscarriages, pregnancy complications, and low birth weight babies than women who have adequate iodine intakes. However, iodine deficiency has its most damaging effects on the developing fetus.
Iodine deficiency is the leading cause of preventable mental retardation worldwide. Children born to iodine-deficient mothers have a condition called cretinism. Cretinism involves severe and permanent brain damage. These children have mental retardation and developmental disorders such as deafness, mutism, and inability to control muscle movements. Iodine deficiency in newborns and infants also results in abnormal brain development and retardation.
Pregnant and breastfeeding women must be especially careful to get enough iodine, since iodine deficiency has its greatest effect on the fetus and newborn. Vegans, who do not eat animal products and depend on soy for much of their protein, are at higher risk of iodine deficiency than the general population.
Amiodarone (Cordarone) a drug used to prevent irregular heart rhythms, contains enough iodine that it may affect thyroid function.
Some foods contain substances called goitrogens that interfere with the body’s ability to absorb or use iodine. These include broccoli, cabbage, cauliflower, and brussel sprouts. Other foods that contain goitrogens are canola oil, soybeans, turnips, peanuts, and cassava. These foods should not cause iodine deficiency unless they are tine mainstay of a very limited diet.
Selenium deficiency amplifies the effects of iodine deficiency. Vitamin A deficiency may amplify iodine deficiency.
Complications of iodine deficiency are discussed above. Iodine excess rarely is caused by diet, although an excess of thyroid hormones may result from other causes.
In developed countries, parents should have few concerns about their healthy children getting enough iodine, so long as they use iodized table salt.
Food and Nutrition Board, Institute of Medicine. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Cooper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. Washington, DC: National Academy Press, 2001, pp. 162-177. http://books.nap.edu/books/0309072794/html/.
Lieberman, Shari and Nancy Bruning. The Real Vitamin and Mineral Book: The Definitive Guide to Designing Your Personal Supplement Program, 4th ed. New York: Avery, 2007.
Pressman, Alan H. and Sheila Buff. The Complete Idiot’s Guide to Vitamins and Minerals, 3rd ed. Indianapolis, IN: Alpha Books, 2007.
International Council for the Control of Iodine Deficiency Disorders. < http://indorgs.virginia.edu/iccidd> .
Linus Pauling Institute. Oregon State University, 571 Weniger Hall, Corvallis, OR 97331-6512. Telephone: (541) 717-5075. Fax: (541) 737-5077. Website: <http://lpi.oregonstate.edu>.
Higdon, Jane. ‘Iodine.’ Linus Pauling Institute-Oregon State University, April 11, 2003. <http://lpi.oregonstate.edu/infocenter/minerals/iodine> .
International Council for the Control of Iodine Deficiency Disorders. ‘Iodine Deficiency Disorder (IDD).’ August 18, 2005. < http://indorgs.virginia.edu/iccidd/aboutidd.htm>.
Lee, Stephanie L. ‘Iodine Deficiency.’ eMedicine.com, July 27, 2006. <http://www.emedicine.com/med/ topic.1187htm> .
Medline Plus. ‘Iodine.’ U. S. National Library of Medicine, November 1, 2006. <http://www.nlm.nih/gov/medlineplus/druginfo/natural/patient-iodine.html> .
Mercer, L. Preston. ‘Iodine.’ American Society for Nutrition, 2006. <http://jn.nutrition.org/nutinfo> .
Northwesternutrition ‘Nutrition Fact Sheet: Iodine.’ Northwestern University, September 21, 2006. <http://www.feinberg.northwestern.edu/nutrition/factsheets/iodine.html>.