iodine

What can high-iodine foods do for you?

  • Help ensure proper thyroid gland functioning

What events can indicate a need for more high-iodine foods?

  • Goiter (enlargement of the thyroid gland)
  • Fatigue
  • Weakness
  • Depression
  • Weight gain

Concentrated food sources of iodine include sea vegetables, yogurt, cow's milk, eggs, strawberries and mozzarella cheese.

 

Description

What is Iodine?

If you backpack in the mountains, you may have used iodine tablets to purify your drinking water. Or, perhaps you've used an iodine-based disinfectant to clean a minor skin wound. But did you know that iodine is essential to life?

Iodine, a trace mineral, is required by the body for the synthesis of the thyroid hormones, thyroxine (T4) and triiodothyronine (T3). (T4 contains 4 iodine atoms. When one of the iodine atoms is stripped off of T4, it becomes T3, with 3 iodine atoms remaining.)

Under normal circumstances, your body contains approximately 20 to 30 mg of iodine, most of which is stored in your thyroid gland, located in the front of your neck, just under your voice box. Smaller amounts of iodine are also found in lactating mammary glands, the stomach lining, salivary glands, and in the blood.

How it Functions

What is the function of iodine?

As a component of the thyroid hormones thyroxine (T4) and triiodothyronine (T3), iodine is essential to human life. Without sufficient iodine, your body is unable to synthesize these hormones, and because the thyroid hormones regulate metabolism in every cell of the body and play a role in virtually all physiological functions, an iodine deficiency can have a devastating impact on your health and well-being.

Regulating thyroid hormones

The synthesis of thyroid hormones is tightly controlled. When the amount of thyroid hormone in your blood drops, the pituitary gland secretes a hormone called thyroid-stimulating hormone (TSH). As its name suggests, TSH then stimulates the thyroid gland to increase its uptake of iodine from the blood, so that more thyroxine (T4) can be synthesized. When necessary, thyroxine is then converted to the metabolically active triiodothyronine (T3), a process that involves removing one iodine atom from T4.

Several other physiological functions for iodine have been suggested. Iodine may help inactivate bacteria, hence its use as a skin disinfectant and in water purification. Iodine may also play a role in the prevention of fibrocystic breast disease, a condition characterized by painful swelling in the breasts, by modulating the effect of the hormone estrogen on breast tissue. Finally, researchers hypothesize that iodine deficiency impairs the function of the immune system and that adequate iodine is necessary to prevent miscarriages.

Deficiency Symptoms

What are deficiency symptoms for iodine?

In the early part of the 20th century, iodine deficiency was quite common in the United States and Canada. However, this problem has since been almost completely resolved by the use of iodized salt. In addition, iodine is now added to animal feed, which has increased the iodine content of commonly consumed foods, including cow's milk.

Unfortunately, in countries where iodized salt is not commonly consumed, iodine deficiency remains a signficant problem. Dietary deficiency of this vital mineral results in decreased synthesis of thyroid hormone.

Goiter, or enlargement of the thyroid gland, is usually the earliest symptom of iodine deficiency. The enlargement of the thyroid results from overstimulation of the thyroid gland by thyroid stimulating hormone (TSH), as the body attempts to produce thyroid hormones despite the lack of available iodine.

Goiter is more common in certain geographical areas of the world, and is attributed to lack of iodine in the diet as well as to the consumption of certain foods, called goitrogens, that block the absorption and utilization of iodine. These foods include cruciferous vegetables, soy products, cassava root, mustard, and millet. Drinking water obtained from contaminated wells may also contain goitrogenic substances.

Iodine deficiency may eventually lead to hypothyroidism, which causes a variety of symptoms including fatigue, weight gain, weakness and/or depression. Interestingly, iodine deficiency can also cause hyperthyroidism, a condition characterized by weight loss, rapid heart beat, and appetite fluctations.

Severe iodine deficiency during pregnancy or infancy causes cretinism, a condition characterized by hypothyroidism leading to failure of the thyroid gland and/or severe mental retardation, stunted physical growth, deafness, and spasticity. If discovered in its initial stages, cretinism can be corrected with iodine supplementation.

Toxicity Symptoms

What are toxicity symptoms for iodine?

Accidental overdose of iodine from medications or supplements in amounts exceeding one gram may cause burning in the mouth, throat and stomach and/or abdominal pain, nausea, vomiting, dirarrhea, weak pulse, and coma.

It is difficult to take in too much iodine from food sources alone. It is estimated that men and women consume at most 300 mcg and 210 mcg of iodine per day, respectively. In general, even high intakes of iodine from food are well-tolerated by most people.

However, in certain circumstances, excessive consumption of iodine can actually inhibit the synthesis of thyroid hormones, thereby leading to the development of goiter (enlargement of the thyroid gland) and hypothyroidism. Excessive iodine intake may also cause hyperthyroidism, thyroid papillary cancer, and/or iodermia (a serious skin reaction).

In an attempt to prevent these symptoms of iodine toxicity, the Institute of Medicine established the following Tolerable Upper Intake Levels (TUL) for iodine:

  • 1-3 years: 900 mcg
  • 4-8 years: 300 mcg
  • 9-13 years: 600 mcg
  • 14-18 years: 900 mcg
  • 19 years and older: 1,100 mcg
  • Pregnant women 14-18 years: 900 mcg
  • Pregnant women 19 years and older: 1,100 mcg
  • Lactating women 14-18 years: 900 mcg
  • Lactating women 19 years and older: 1,100 mcg

It is important to note that if you have an autoimmune thyroid disease (for example, Grave's disease or Hashimoto's disease) or if you have experienced an iodine deficiency at some point in your life, you may be more susceptible to the dangers of excessive iodine consumption, and may, therefore, need to monitor your intake of iodine more carefully.

Impact of Cooking, Storage and Processing

How do cooking, storage, or processing affect iodine?

Food processing practices often increase the amount of iodine in foods. For example, the addition of potassium iodide to table salt to produce "iodized" salt has dramatically increased the iodine intake of people in developed countries. In addition, iodine-based dough conditioners are commonly used in commercial bread-making, which increases the iodine content of the bread.

Factors that Affect Function

What factors might contribute to a deficiency of iodine?

The absorption and/or utilization of iodine is inhibited by components of certain foods. These food components, called goitrogenic compounds, are found primarily in cruciferous vegetables (for example, cabbage and broccoli), soybean products, cassava root, peanuts, mustard, and millet.

Over consumption of these foods may lead to thyroid problems by reducing the amount of available iodine for the manufacture of thyroid hormones. It is believed that cooking can inactivate the goitrogenic compounds in these foods, thereby eliminating their negative impact on iodine status.

Drug-Nutrient Interactions

What medications affect iodine?

Amiodarone, a drug most commonly sold under the brand name Cordarone (TM), is sometimes used to treat irregular heart beat. This medication contains iodine and can disrupt proper thyroid function.

Similarly, erythrosine, a red coloring agent commonly used in foods and medications, also contains significant amounts of iodine and may also impact thyroid activity.

Nutrient Interactions

How do other nutrients interact with iodine?

The conversion of thyroxine (T4) to triiodthyronine (T3) requires the removal of an iodine molecule from T4. This reaction requires the mineral selenium. The iodine molecule that is removed gets returned to the body's pool of iodine and can be reused to make additional thyroid hormones.

If your body is deficient in selenium, the conversion of T4 to T3 is slowed, and less iodine is available for the thryoid to use in making new hormones.

Animal studies have shown that arsenic interferes with the uptake of iodine by the thyroid, leading to goiter. In addition, dietary deficiency of vitamin A, vitamin E, zinc and/or iron can exaggerate the effects of iodine deficiency.

Health Conditions

What health conditions require special emphasis on iodine?

Iodine may play a role in the prevention and/or treatment of the following health conditions:

  • Cognitive impairment
  • Cretinism
  • Fibrocystic breast disease
  • Goiter
  • Hyperthyroidism
  • Hypothyroidism
  • Multiple miscarriages

Form in Dietary Supplements

What forms of iodine are found in dietary supplements?

The elemental form of iodine is available in dietary supplements as iodine caseinate and in products that contain kelp. Many supplements contain iodine complexed with potassium or sodium, called potassium iodide or sodium iodide, respectively.

Food Sources

Introduction to Nutrient Rating System Chart

The following chart shows the foods which are either excellent, very good or good sources of this nutrient. Next to each food name you will find the following information: the serving size of the food; the number of calories in one serving; DV% (percent daily value) of the nutrient contained in one serving (similar to other information presented in the website, this DV is calculated for 25-50 year old healthy woman); the nutrient density rating; and the food's World's Healthiest Foods Rating. Underneath the chart is a table that summarizes how the ratings were devised. For more detailed information on our Nutrient Rating System, please click here.

 

Foods Ranked as quality sources of:
iodine
Food Serving
Size
Cals Amount
(mcg)
DV
(%)
Nutrient
Density
World's
Healthiest
Foods Rating
Sea vegetables 1.50 tsp 1.1 225.00 150.0 2500.0 excellent
Yogurt, Cow Milk, Low Fat 1 cup 155.1 87.22 58.1 6.8 very good
Milk, Cow, 2% 1 cup 121.2 58.56 39.0 5.8 very good
Egg, Hen, Whole, Boiled 1 each 68.2 23.76 15.8 4.2 very good
Strawberries, Fresh 1 cup 43.2 12.96 8.6 3.6 very good
Mozzarella Cheese, Part Skim, Shredded 1 oz-wt 72.1 10.09 6.7 1.7 good
World's Healthiest
Foods Rating
Rule
excellent DV>=75% OR Density>=7.6 AND DV>=10%
very good DV>=50% OR Density>=3.4 AND DV>=5%
good DV>=25% OR Density>=1.5 AND DV>=2.5%

Public Health Recommendations

What are current public health recommendations for iodine?

In 2000, the Institute of Medicine at the National Academy of Sciences developed new Dietary Reference Intakes for iodine. Adequate Intakes were established for children up to one year old, and Recommended Dietary Allowances were determined for all people over one year old. These recommendations appear below:

  • 0-6 months: 110 mcg
  • 7-12 months: 130 mcg
  • 1-8 years: 90 mcg
  • Boys 9-13 years: 120 mcg
  • Girls 9-13 years: 120 mcg
  • Boys 14-18 years: 150 mcg
  • Girls 14-18 years: 150 mcg
  • Men 19 years and older: 150 mcg
  • Women 19 years and older: 150 mcg
  • Pregnant women 14 years and older: 220 mcg
  • Lactating women 14 years and older: 290 mcg

References

  • Delange F. The role of iodine in brain development. Proc Nutr Soc 2000 Feb;59(1):75-9.
  • Dunn JT, Dunn AD. Update on intrathyroidal iodine metabolism. Thyroid 2001 May;11(5):407-14.
  • Feldt-Rasmussen U. Iodine and cancer. Thyroid 2001 May;11(5):483-6.
  • Groff JL, Gropper SS, Hunt SM. Advanced Nutrition and Human Metabolism. West Publishing Company, New York, 1995.
  • Institute of Medicine. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. National Academy Press: Washington DC, 2001.
  • Lininger SW, et al. A-Z guide to drug-herb-vitamin interactions. Prima Health, Rocklin, CA, 2000.
  • Mahan K, Escott-Stump S. Krause's Food, Nutrition, and Diet Therapy. WB Saunders Company; Philadelphia, 1996.
  • Rasmussen LB, Ovesen L, Bulow I et al. Relations between various measures of iodine intake and thyroid volume, thyroid nodularity, and serum thyroglobulin. Am J Clin Nutr 2002 Nov;76(5):1069-76.
  • Roti E, Uberti ED. Iodine excess and hyperthyroidism. Thyroid 2001 May;11(5):493-500.
  • Ruwhof C, Drexhage HA. Iodine and thyroid autoimmune disease in animal models. Thyroid 2001 May;11(5):427-36.
  • Spitzweg C, Heufelder AE, Morris JC. Thyroid iodine transport. Thyroid 2000 Apr;10(4):321-30.
  • Venturi S, Donati FM, Venturi A, et al. Role of iodine in evolution and carcinogenesis of thyroid, breast and stomach. Adv Clin Path 2000 Jan;4(1):11-7.

This page was updated on: 2004-11-21 11:17:45
© 2002 The George Mateljan Foundation