UNIVERSITY PUTRA MALAYSIAFACULTY OF MEDICINE AND HEALTH SCIENCESDEPARTMENT OF NUTRITION SCIENCESIODINEByMohammed ElluluMICRONUTRIENTS IN HEALTH AND DISEASE
Introduction In 1896, Baumann determined the association ofiodine with the thyroid gland. In 1914 Kendall, with revisions by Harrington in1926, described the hormone complexessynthesized by the thyroid gland using iodine thatare so integral to human growth and development. Recent work has demonstrated iodine, involvedthrough peroxidases in enzymatic activity andproduction of numerous active metabolites in thehuman body.2
Absorption, Transport, and Storage Iodine is usually ingested as an iodide or iodatecompound and is rapidly absorbed in the intestine. Iodine entering the circulation is actively trapped by thethyroid gland. The active transport of iodine is likely to be based oncotransport of sodium and iodine in capillaries. Anion thiocyanate inhibits the active transport. In addition to trapping iodine in thyroid cells, follicularcells also synthesize the glycoprotein, thyroglobulin (Tg),from carbohydrates and amino acids (including tyrosine)obtained from the circulation.3
Thyroglobulin moves into the lumen of the folliclewhere it becomes available for hormone production. Thyroid peroxidase (TPO), a membrane-boundhem-containing glycoprotein, catalyzes theoxidation of the iodide to its active form, I2, andthe binding of this active form to the tyrosine inthyroglobulin to form mono- or diiodotyrosine (MITor DIT). These in turn combine to form the thyroid hormonestriiodothyronine (T3) and thyroxine (T4).Absorption, Transport, and Storage4
Recommended IntakesTable 1: Recommended Dietary Allowances (RDAs) for IodineAge Male Female Pregnancy LactationBirth to 6 months 110 mcg* 110 mcg* (* Adequate intake)7–12 months 130 mcg* 130 mcg*1–3 years 90 mcg 90 mcg4–8 years 90 mcg 90 mcg9–13 years 120 mcg 120 mcg14–18 years 150 mcg 150 mcg 220 mcg 290 mcg19+ years 150 mcg 150 mcg 220 mcg 290 mcg7
Sources of IodineFood Seaweed (such as kelp), seafood, dairy products.Ionized-Salt More than 70 countries, including the United Statesand Canada, have salt iodization programs. FDA approved potassium iodide and cuprous iodidefor salt iodization while the WHO recommends theuse of potassium iodate due to its greater stability.Supplements8
Iodine Deficiency Iodine deficiency has multiple adverse effects ongrowth and development, and is the most commoncause of preventable mental retardation in theworld. Resulted mainly from inadequate thyroid hormoneproduction. During pregnancy and early infancy, iodinedeficiency can cause irreversible effects. Under normal conditions, the body tightly controlsthyroid hormone concentrations via TSH.9
TSH secretion increases when iodine intake falls belowabout 100 mcg/day. TSH increases thyroidal iodine uptake from the bloodand the production of thyroid hormone. However, very low iodine intakes can reduce thyroidhormone production even in the presence of elevatedTSH levels. If iodine intake falls below approximately 10–20mcg/day, hypothyroidism occurs. Goiter is the earliest clinical sign of iodine deficiency.Iodine Deficiency10
Iodine Deficiency In pregnant women, iodine deficiency can cause majorneurodevelopmental deficits and growth retardation inthe fetus, as well as miscarriage and stillbirth. Chronic, severe iodine deficiency in utero causescretinism (mental retardation). Stunted growth, delayed sexual maturation. In infants and children, less severe iodine deficiency cancause neurodevelopmental deficits such as somewhatlower-than-average intelligence. Mild to moderate maternal iodine deficiency associatedwith an increased risk for attention deficit hyperactivitydisorder in children.11
Classification of hypothyroidism123ry2ry1ry4ry
Iodine and HealthFetal and infant development During early pregnancy, the fetus depends entirelyon maternal T4 and maternal iodine intake. Production of T4 increases by approximately 50%during pregnancy, requiring a concomitant increasein maternal iodine intake. Breast milk contains iodine, although concentrationsvary based on maternal iodine levels.13
Iodine and HealthFibrocystic breast disease Is a benign condition characterized by lumpy,painful breasts and fibrosis. It affects women ofreproductive age, also occur during menopause,especially in women taking estrogens. Breast tissue has a high concentration of iodine,especially during pregnancy and lactation. Some research suggests that iodine supplementationmight be helpful for fibrocystic breast disease.14
Radiation-induced thyroid cancer Thyroidal uptake of radioactive iodine is higher inpeople with iodine deficiency than in people withiodine sufficiency. The FDA has approved potassium iodide as athyroid-blocking agent to reduce the risk of thyroidcancer in radiation emergencies involving therelease of radioactive iodine (as nuclear accidents).Iodine and Health15
Assessment of Iodine Status There are several additional indicators that are used toassess thyroid function, such as T4 and T3, but these areless accurate in reflecting iodine status since conversionof T4 to T3 and cellular uptake is so responsive toperipheral need. Urinary iodine reflects iodine sufficiency, and outputdecreases with diminished intake. Thyroid size, either estimated by palpation or usingultrasound volume determination, reflects iodine statussince deficiency results in thyroid enlargement, or goitre.16
Assessment of Iodine Status17 In adults, where long-standing thyroid enlargement fromiodine deficiency may be minimally responsive tocorrected iodine intake, palpation may be misleadingand could overestimate the current level of iodinesufficiency. TSH is produced in response to decreased iodine intakeand diminished thyroid hormone production and is usedas a measure of iodine status. Uptake of radioactive iodine isotopes can be used toscan the gland, and determine the affinity of the glandto introduced iodine, and is a measure of deficiency.
Iodine interaction18Major Highly clinically significant. Avoid combinations; the risk ofthe interaction outweighs the benefit.Moderate Moderately clinically significant. Usually avoidcombinations; use it only under special circumstances.Minor Minimally clinically significant. Minimize risk; assess riskand consider an alternative drug, take steps to circumvent theinteraction risk and/or institute a monitoring plan.
Iodine interaction19Medications for an overactive thyroid (Antithyroiddrugs) Interaction Rating Major. Taking iodine along with medications for anoveractive thyroid might decrease the thyroid toomuch. Some of these medications include methimazole,and potassium iodide.
Iodine interaction20Amiodarone Interaction Rating: Moderate. Amiodarone contains iodine. Taking iodine supplementsalong with amiodarone might cause too much iodine in theblood. Too much iodine in the blood can cause side effectsthat affect the thyroid.Medications for high blood pressure (ACE inhibitors)Interaction Rating: Moderate. Decreases quickly the body gets rid of potassium. Mostiodide supplements contain potassium. Taking potassiumiodide along with some medications for high blood pressuremight cause too much potassium in the body.
Iodine interaction21 Selenium is required for converting of thyroxine (T4) totriiodthyronine (T3); the removal of iodine molecule from T4. The iodine molecule that is removed gets returned to thebodys pool of iodine and can be reused to make additionalthyroid hormones. If body is deficient in selenium, the conversion of T4 to T3 isslowed, and less iodine is available for the thryoid to use inmaking new hormones. Animal studies have shown that arsenic interferes with theuptake of iodine by the thyroid, leading to goiter. In addition, dietary deficiency of vitamin A, vitamin E, zincand/or iron can exaggerate the effects of iodine deficiency.
References22 1. National Research Council, Committee to Assess the Health Implications ofPerchlorate Ingestion. Health Implications of Perchlorate Ingestion. Washington, DC:The National Academies Press, 2005. 2. Institute of Medicine, Food and Nutrition Board. Dietary Reference Intakes forVitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese,Molybdenum, Nickel, Silicon, Vanadium, and Zinc. Washington, DC: NationalAcademy Press, 2001. 3. World Health Organization. United Nations Childrens Fund & InternationalCouncil for the Control of Iodine Deficiency Disorders. Assessment of iodinedeficiency disorders and monitoring their elimination. 3rd ed. Geneva, Switzerland:WHO, 2007. 4. Patrick L. Iodine: deficiency and therapeutic considerations. Altern Med Rev.2008 Jun;13(2):116-127. 5. Zimmermann MB. Iodine deficiency. Endocr Rev. 2009 Jun;30(4):376-408. 6. Zimmermann MB, Jooste PL, Pandav CS. Iodine-deficiency disorders. Lancet.2008 Oct 4;372(9645): 1251-1262.
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