Investigating Iodine

Iodine is a trace mineral that your body uses to synthesize the thyroid hormones, thyroxine (T4) and triiodothyronine (T3). T4 contains 4 iodine atoms. When the amount of thyroid hormone in your blood drops, your pituitary gland secretes a hormone called thyroid-stimulating hormone (TSH). As its name suggests, TSH then stimulates your thyroid gland, located in the front of your neck, just under your voice box, to increase its uptake of iodine from your blood, so it can make more thyroxine (T4). When necessary, thyroxine is then converted to the metabolically active triiodothyronine (T3), a process that involves removing one iodine atom from T4. When one of the iodine atoms is stripped off of T4, it becomes T3, with 3 iodine atoms remaining. 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. Without sufficient iodine, your body is unable to synthesize these hormones, and because your thyroid hormones regulate metabolism in every cell of your body and plays a role in virtually all physiological functions, an iodine deficiency can have a devastating impact on your health and well-being. If your body is deficient in selenium, the conversion of T4 to T3 is slowed, and less iodine is available for your thryoid to use in making new hormones.

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

Iodine may help inactivate bacteria, hence its use as a skin disinfectant and in water purification. Iodine may also play a role in preventing fibrocystic breast disease, a condition characterized by painful swelling in the breasts, by modulating the effect of the hormone estrogen on breast tissue. Iodine deficiency may impair the function of your immune system. Finally, adequate iodine may prevent miscarriages.

Goiter, or enlargement of the thyroid gland, is usually the earliest visible 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 increased amounts of thyroid hormone. Goiter can occur for many other reasons as well, but iodine deficiency is among the most common causes worldwide. Goiter is more common in certain geographical areas of the world where iodine is lacking in the diet and where selenium is lacking in the soil, because selenium is directly involved with certain activities of the thyroid gland. Arsenic interferes with the uptake of iodine by your thyroid, leading to goiter. In addition, dietary deficiency of vitamin A, vitamin E, zinc, or iron can exaggerate the effects of iodine deficiency.

In the early part of the 20th century, iodine deficiency was common in the United States and Canada; however, this problem has since been almost completely resolved by the use of iodized salt. Unfortunately, in countries where iodized salt is not commonly consumed, iodine deficiency remains a significant problem. Dietary deficiency of iodine results in decreased synthesis of thyroid hormone.

Iodine deficiency may eventually lead to hypothyroidism, which causes a variety of symptoms including fatigue, weight gain, weakness,  and depression. Interestingly, iodine deficiency can also cause hyperthyroidism, a condition characterized by weight loss, rapid heart beat, and appetite fluctuations  Severe iodine deficiency during pregnancy or infancy causes cretinism, a condition characterized by hypothyroidism leading to failure of the thyroid gland, severe mental retardation, stunted physical growth, deafness, and spasticity. If discovered in its initial stages, cretinism can be corrected with iodine supplementation.

Accidental overdose of iodine from medications or supplements in amounts exceeding one gram may cause burning in the mouth, throat, and stomach, 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 and hypothyroidism. Excessive iodine intake may also cause hyperthyroidism, thyroid papillary cancer, or iodermia (a serious skin reaction).

In an attempt to prevent these symptoms of iodine toxicity, the Institute of Medicine established the Tolerable Upper Intake Level (TUL) for iodine at 1,100 micrograms for adults aged 19 and over. If you have an autoimmune thyroid disease, such as 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.

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. Cans are often washed in an iodine solution, increasing the iodine in canned foods.

Because absorption of iodine from the digestive tract is very thorough, deficiency of iodine typically occurs from too little intake of iodine-containing foods. However, two phytochemicals can interfere with iodine utilization by your thyroid gland, but only under very specific circumstances. These circumstances involve simultaneous dietary deficiency of iodine or selenium (or both) and imbalanced overall dietary intake. Isoflavones, most commonly found in soy, and thiocyanates, most commonly produced in your body from glucosinolates in brassica vegetables like kale.  There’s no evidence showing problems with iodine metabolism by the thyroid gland when either soy or brassica vegetables are eaten in moderate amounts in an overall balanced diet that also contains appropriate amounts of iodine and selenium. Because soy and brassica vegetables provide so many health benefits, there’s probably no reason to eliminate these foods from the diet for iodine-related reasons. However, people with a history of thyroid problems, poor dietary balance and deficient intake of iodine or selenium, should consult with a healthcare provider to decide about the role of these foods in health support.

The amount of iodine found in most natural foods is typically quite small and varies depending on environmental factors such as the soil concentration of iodine and the use of fertilizers. Some of the richest food sources of iodine are often processed foods that contain iodized salt, and breads that contain iodate dough conditioners.

Kelp, dulse, kombu, arame, cranberries, asparagus, wakame, iodized salt, potatoes, soy nuts, turnips, navy beans, and beets are excellent source of iodine. Peppers, commercially baked bread, cucumbers, carrots, rice, leaf lettuce, cabbage, canned corn, dried prunes, and strawberries are very good sources of idone. Good sources include tomatoes, lima beans, barley, turnip greens, and oats.

Food

Serving Size

Amount (µg)

DV

Dried Kelp

1 tablespoon

2000

1333%

Dulse

7 grams (1/3 cup)

1169

779%

Kombu

1 tablespoon

780

520%

Arame

1 tablespoon

730

487%

Cranberries

4 ounces

400

267%

Asparagus

4.4 ounces

138

92%

Chlorella

1 ounce

112

75%

Spinach

4.4 ounces

83

55%

Wakame

1 tablespoon

80

53%

Iodized Salt

1 gram (0.18 teaspoons)

77

51%

Potato

1 medium, baked with skin

60

40%

Soynuts

1/4 cup

60

40%

Turnips

4.4 ounces

42

28%

Navy Beans

1/2 cup, cooked

32

21%

Beets

4.4 ounces

29

20%

Peppers

4.4 ounces

25

17%

Bread

1 slice, commercially baked

25

17%

Cucumber

4.4 ounces

24

16%

Carrots

4.4 ounces

18

12%

Rice

4.4 ounces

18

12%

Leaf Lettuce

9 ounces

17

11%

Cabbage

4.4 ounces

15

10%

Canned Corn

1/2 cup

14

9.3%

Dried Prunes

5 medium

13

9%

Strawberries

1 cup

13

9%

Tomatoes

4.4 ounces

8

5%

Lima Beans

1/2 cup

8

5%

Barley

4.4 ounces

6

4%

Turnip Greens

5 ounces, raw

6

4.%

Oats

4.4 ounces

6

4%

Green Peas

1/2 cup

3.5

2.3%

Banana

1 medium

3

2%

Green Beans

1/2 cup

3

2%


This blog uses the latest nutritional data available from the USDA (United States Department of Agriculture), and the FDA (United States Food and Drug Administration), as well as nutritional data provided by food growers and manufacturers about their products. We believe the information on this website to be accurate. However, we are not responsible for typographical or other errors. Nutrition information for recipes is calculated by Living Cookbook based on the ingredients in each recipe based on statistical averages. Nutrition may vary based on methods of preparation, origin and freshness of ingredients, and other factors.

This blog is not a substitute for the services of a trained health professional. Although we provide nutritional information, the information on this blog is for informational purposes only. No information offered by or through this blog shall be construed as or understood to be medical advice or care. None of the information on this blog should be used to diagnose or treat any health problem or disease. Consult with a health care provider before taking any product or using any information on this blog. Please discuss any concerns with your health care provider.

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7 thoughts on “Investigating Iodine

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