Iodine

Overview

Iodine’s only known function is the role it plays in the various thyroid hormones, diiodotyrosine, triiodothryonine (T3), and thyroxine (T4). Dietary iodine is converted to iodide in the GI tract where it is easily absorbed and transported to the thyroid gland. In the thyroid gland, iodine is stored on the tyrosine moiety of a protein complex called thyroglobulin.

Iodine metabolism and thyroid hormone production are regulated by a negative feedback hormonal control system. A decline in blood thyroid hormone triggers the hypothalamus to release thyroid releasing hormone (TRH) which in turn signals the anterior pituitary to release thyroid stimulating hormone (TSH). An increase in TSH stimulates the thyroid gland to increase the uptake of iodine and synthesize more thyroid hormone. TSH also stimulates the thyroid gland to produce enzymes, which cleave thyroglobulin to release thyroid hormone into circulation for delivery to cells throughout the body. If the thyroid gland is damaged or absent, the basal metabolic rate can decline to as low as 55 percent of normal, resulting in impaired growth and development. When the thyroid gland is hyperactive, the basal metabolic rate can go up as high as 160 percent of normal, causing tachycardia, nervousness, and excitability.

Dosage Info

Dosage Range

Dosages typically used range from 50-250mcg daily. Occasionally doses as high as 0.08mg/kg (5.6mg for 70kg adult) have been used for fibrocystic breast disease. (1)

Most Common Dosage

150mcg daily.

Dosage Forms

Tablets, capsules, and liquid.

Adult RDI

150mcg

Adult ODA

250mcg

RDA

  • Infants < 6 months: 110mcg (Adequate Intake, AI)
  • Infants 7-12 months: 130mcg (AI)
  • Children 1-8 years: 90mcg
  • Children 9-13 years: 120mcg
  • Adults >14 years: 150mcg
  • Pregnancy: 220mcg
  • Lactation: 290mcg

Active Forms

Potassium iodide (SSKI or saturated solution of potassium iodide), sodium iodide, iodine caseinate, aqueous (diatomic) iodine.

Absorption

Iodine is readily absorbed from the intestines.

Toxicities & Precautions

General

Iodine is a relatively benign trace element which is nontoxic at dosages 10 to 20 times above normal daily needs. The thyroid gland absorbs iodine, but thyroid synthesis remains normal.

Side Effects

Chronic excessive intake of iodine can cause an enlargement of the thyroid gland resembling goiter. (2) The condition is called “iodine goiter."

Functions in the Body

Thyroid:

Involved in the activity and function of the thyroid hormone. (3) The iodine-dependent thyroid hormone regulates cellular oxygen consumption, basal metabolism, and energy production throughout the body. As a result, the thyroid hormone controls a variety of biological and physiological activities including body temperature, physical growth, reproduction, neuromuscular function, the synthesis of proteins, and the growth of skin and hair.

Clinical Applications

Pregnancy

During pregnancy iodine deficiency may occur and this could impair thyroid function. (4) Results of a study suggest that due to iodine deficiency, TSH levels fell lower as the pregnancy advanced causing a significant negative correlation with thyroid volume. (5)

Fibrocystic Breast Disease

Iodine-deficient lab animals develop lesions that resemble human fibrocystic breast disease. (6) In a study with 715 women, all women were cyst-free and 70 percent were pain free within 4 months using diatomic iodine. (7) , (8) A review of studies utilizing sodium iodide, protein-bound iodide, and molecular iodine revealed that molecular iodine was the most effective form of treatment for fibrocystic breast disease. (9)

Goiter Prevention

Iodine supplementation has been shown to prevent the recurrence of goiter after thyroid surgery in people who live in an iodine-deficient area. (10) In a year-long study, iodine was slightly more effective than levothyroxine at reducing the size of thyroid gland in people with goiters. (11) The use of iodized salt has proven to be an effective form of iodine supplementation in iodine-deficient areas. (12)

Symptoms and Causes of Deficiency

A deficiency of iodine results in the enlargement of the thyroid gland, a condition known as goiter. The introduction of iodized salt has made iodine deficiency and the development of goiters uncommon in the United States and other developed countries.

Dietary Sources

Iodized salt is the most common source of iodine in the United States. Iodine-rich foods include seafood, sea vegetables (seaweed), kelp, and vegetables grown on iodine-rich soils.

References

  1. View Abstract: Ghent WR, Eskin BA, Low DA, Hill LP. Iodine replacement in fibrocystic disease of the breast. Can J Surg. Oct1993;36(5):453-460.
  2. View Abstract: Kanno J, Onodera H, Furuta K. Tumor-promoting effects of both iodine deficiency and iodine excess in the rat thyroid. Toxicol Pathol. 1992;20(2):226-35.
  3. View Abstract: De Vijlder JJ. Primary congenital hypothyroidism: defects in iodine pathways. Eur J Endocrinol. Oct2003;149(4):247-56.
  4. View Abstract: Glinoer D. The regulation of thyroid function during normal pregnancy: importance of the iodine nutrition status. Best Pract Res Clin Endocrinol Metab. Jun2004;18(2):133-52.
  5. View Abstract: Dominguez I, Reviriego S, Rojo-Martinez G, et al. Iodine deficiency and thyroid function in healthy pregnant women. Med Clin (Barc). Apr2004;122(12):449-53.
  6. View Abstract: Krouse TB, et al. Age-related Changes Resembling Fibrocystic Disease in Iodine-blocked Rat Breasts. Arch Pathol Lab Med. Nov1979;103(12):631-34.
  7. Eskin B, Ghent W. Reported in: Medical World News. Jan1988:25.
  8. View Abstract: Ghent WR, et al. Iodine replacement in fibrocystic disease of the breast. Can J Surg. Oct1993;36(5):453-60.
  9. View Abstract: Ghent WR, et al. Iodine Replacement in Fibrocystic Disease of the Breast. Can J Surg. Oct1993;36(5):453-60.
  10. View Abstract: Rzepka AH, et al. Effectiveness of Prophylactic Therapy on Goiter Recurrence in an Area with Low Iodine Intake--A Sonographic Follow-up Study. Clin Investig. Dec1994;72(12):967-70.
  11. View Abstract: Feldkamp J, et al. Therapy of Endemic Goiter with Iodide or l-thyroxine in Older Patients. Dtsch Med Wochenschr. Dec1996;121(51-52):1587-91.
  12. View Abstract: Meng W, et al. Nutritional Iodine Supply in Germany. Results of Preventive Measures. Z Arztl Fortbild Qualitatssich. Dec1997;91(8):751-56.