Trace Elements at LLSG Iodine (I)

TITLE	Iodine (I)
SYNONYMS/FORMS
GENERAL INFORMATION	Iodine is an essential trace element that is required for the synthesis of thyroid hormones by the thyroid gland. Thyroid hormones (T3 and T4) stimulate many metabolic processes and increase the basal metabolic rate. These hormones are essential for normal growth and development. Iodine is especially important in pregnant women. In the early stages of pregnancy, the fetus is entirely dependent on the maternal thyroid hormones for normal development of the brain. Iodine deficiency during pregnancy can result in mental retardation and other developmental problems in fetus. The recommended daily iodine intake is 90-120 ug for children (1-12 years) and 150 ug for adults. In pregnancy there is an increased requirement for iodine, and a daily intake of 200 ?g is recommended (1). Iodine is absorbed through the GI trace from food, water, or medication. Dietary iodine is converted to the iodide ion before absorption. Once absorbed, it enters the extracellular iodine pool. The thyroid gland extracts amount required for hormone synthesis and the kidney excretes excess iodide (approximately 90% of ingested iodine) into urine (2). Because urinary iodine excretion directly reflects dietary iodine intake, urine iodine analysis is the best test for biochemical assessment of iodine status. It is most commonly used to diagnose Iodine deficiency in a population. The test is also useful to monitor iodine levels in patients taking iodine-containing drugs such as Amiodarone, iodine supplements or radioiodine therapy.
SOURCES/ROUTE OF EXPOSURE	Seaweed and marine fish are rich sources of iodine. Dairy products, eggs, and meat are also rich in iodine. Many multivitamin preparations contain 150 ug of iodine per tablet. Iodized salt: In Canada, salt iodization is mandatory (1g of iodized salt contains about 77 ug of iodine). Excess Iodine Intake: Medication, such as Amiodaron containing 75 mg iodine per 200 mg capsule. Iodine-containing dyes for radiological procedures
DEFICIENCY OR TOXICITY	Deficiency Iodine deficiency can lead to enlargement of thyroid gland (known as a goiter) and impaired thyroid hormone synthesis. The thyroid gland enlarges to maximize the amount of iodine to be extracted from the blood, and if this problem is not corrected, a shortage of thyroid hormone in the body may lead to weakness, weight gain, cold intolerance, dry skin, constipation, and depression (3). Iodine deficiency during pregnancy has been associated with miscarriages, stillbirth, preterm delivery, and mental retardation, short stature, and impaired hearing and speech in children (4). Toxicity Most people can tolerate fairly large amounts of iodine without problems. However, excess iodine intake in some people, especially those who were previously iodine deficient, may lead to hyperthyroidism (Jod-Basedow phenomenon). Paradoxically, rapid excess uptake of iodine may inhibit thyroid hormone synthesis, a condition known as "Wolff-Chaikoff effect". The upper limit of safe daily iodine intake is 1 mg for adults, and it is lower for children. (5).
MONITORING/CLINICAL INTERPRETATION	Urinary iodine excretion can be used as an index of dietary iodine intake. Value <100 ug/day suggests dietary deficiency. Values >460 ug/day may indicate dietary excess, but more frequently suggest recent drug or contrast media exposure. Patients exposed to large amounts of radiographic contrast media or iodine rich drug, such as Amiodarone need to have their iodine levels monitored.
MATRIX CHOICE	The 24-hour urine collection is preferred. If a 24-hour urine collection is not practical, a random urine sample can be used instead. The result of random urine iodine is reported as a ratio of iodine to creatinine. Plasma iodine includes free inorganic iodide and organic iodine bound to the thyroid hormones. Measurement of iodine in plasma was used in history for indirect assessment of the concentration of thyroid hormones. This test has been replaced by direct measurement of the thyroid hormones, TSH, T4 and T3
TREATMENT	Goiter due to iodine deficiency can be treated with iodine supplementation. Long term dietary supplementation of iodine includes iodized salt, iodine rich diet (saltwater fish, milk, and eggs) and iodine in multivitamins.
REFERENCES	1. WHO, UNICEF, ICCIDD. Assessment of iodine deficiency disorders and monitoring their elimination. A guide for program managers, 3rd ed. 2007 http://whqlibdoc.who.int/publications/2007/9789241595827_eng.pdf 2. Iodine. Vitamin and mineral requirements in human nutrition. 2nd ed, 1998. http://whqlibdoc.who.int/publications/2004/9241546123_chap16.pdf 3. Iodine deficiency. eMedicine. http://emedicine.medscape.com/article/122714-overview 4. Iodine deficiency. American Thyroid Association. http://www.thyroid.org/patients/patient_brochures/iodine_deficiency.html 5. Iodine and health. Eliminating iodine deficiency disorders safely through salt iodination. Geneva, World health Organization, 1994. 6. Hollowell JG et al. 1998 Iodine nutrition in the United Stages. Trends and public health implications: Iodine excretion data from national health and nutrition examination surveys I and III (1971-1974 and 1998-1994). J Clin Endocrinol Metab 83:3401-3408, 1998.
TEST INFORMATION REFERENCE RANGES	Urine	Plasma	Hair


January 31, 2012