Unformatted text preview: Iodine
Iodine Deficiency Disorder
Most preventable cause of mental retardation in the world Thyroid Gland Butterfly shaped endocrine gland Located in the neck Absorbs iodine Produces thyroid hormones and calcitonin Functions of Iodine Essential component of thyroid hormones Thyroid hormones control Triiodothyronine (T3) (more potent) Thyroxine (T4) (more prevalent later converted) Regulation of body temperature Basal metabolic rate Growth and Development Critical periods Intense development and rapid cell division is unique for each organ Incomplete development during the critical period may be permanent For ex: folate deficiency may lead to a NTD and may be fatal (anencephaly, spina bifida) Synthesis of Thyroid Hormones Thyroid gland absorbs iodine Thyroglobulin synthesized in thyroid gland T4 and T3 circulate enzyme thyroperoxidase / iodine binds to tyrosine residues on thyroglobulin proteases release T4 (~90%) and T3 (10%) from thyroglobulin T4 converted to more active form T3 Iodine in the body High absorption rates (95100%) 7080% stored in the thyroid gland Conservation, recycling Conversion of T4 to T3 requires selenium Excess lost in urine, sweat Iodine Deficiency Disorders IDD Fetus Spontaneous abortion, stillbirth, congenital anomalies, increased mortality (perinatal, infant), endemic cretinism, deaf mutism Neonate Neonatal Goiter Neonatal hypothyroidism Iodine Deficiency Disorders IDD Child and Adolescent Goiter, juvenile hypothyroidism, impaired mental function, retarded physical development Adult Goiter with potential complications, hypothyroidism, impaired mental function, iodineinduced hyperthyroidism Homeostatic Feedback When levels of thyroid hormone is low When levels of Thyroid hormones increase TSH is common clinical measure of Thyroid Stimulating Hormone (TSH) is secreted from the pituitary gland Increased levels of TSH leads to increased synthesis and release of thyroid hormone TSH levels drop and less Thyroid hormone is made or released Thyroid Hormone levels Goiter When TSH levels remain high the thyroid enlarges to try and meet the needs of the body Euthyroid Growth and Development T3 and T4 working with other hormones influence fetal tissue function, growth and development Development of brain and other neural tissue Cretinism Neurological Myxedematous Visible effects of IDD (cretinism) account for only about 10% of the consequences. A much greater percentage (90%) of IDD consequences remain hidden . Hypothyroidism Causes Iodine deficiency Thyroiditis (inflammation) autoimmune (Hashimoto's Disease) Surgical causes Food Sources Fish Sea vegetables (i.e., seaweed) Other vegetables depending on soil content Not in mountainous regions Andes, Himalayas, Tanzania Iodine Deficiency Hypothyroidism Symptoms Fatigue ;Weakness Weight gain or increased difficulty losing weight Coarse, dry hair Hair loss Dry, rough pale skin Cold intolerance Muscle cramps/aches Constipation Depression Irritability Memory loss Abnormal menstrual cycles Decreased libido
http://www.endocrineweb.com Iodine Status Assessment Goiter classification Urinary iodine concentration (community) TSH (Thyroid Stimulating Hormone) concentration (individual) Other common clinical measures: Ultrasonoagraphy of thyroid volume Serum concentrations: thyroxine (T4) Thyroid Binding Globulin Epidemiological Criteria for Assessing Severity of IDD Based on Median Urinary Iodine Levels (WHO, 1994) Median Value (g/l)
< 20 2049 5099 >100 Severity of IDD Severe IDD Mild IDD Moderate IDD No deficiency Indicator of iodine intake, not thyroid function Supplementation Iodized Salt Cretinism seen in the US into the 1920s Salt is universally and regularly consumed. Costs only US $0.04 per person annually. Manufactured with simple technology Morton salt 1924 Supplementation Iodized oil Irrigation water Given to pregnant women when other form of supplementation is not available Longer lasting but harder to deliver Stored in thyroid and in adipose tissue Other products Iodized Salt Village in Philippines Factory in Mongolia Iodized irrigation water in Xinjiang,China Area of severe iodine deficiency Potassium iodate added to irrigation water in 3 villages; control areas supplied by different irrigation system Maternal urinary iodine increased from <10 to 55 ug/L "iodinated water could reduce infant mortality by approximately half"
DeLong et al, Lancet, 1997; Semba, 2001 Prevalence of Goiter Before/After Salt Iodization Programs Prior to Iodization Columbia In 1945 82% Following Iodization In 1952 37% In 1965 3% Prior to Iodization Guatemala In 1952 39% Following Iodization In 1962 15% In 1965 5% Scrimshaw, 1994 Goitrogens Substances that reduce iodine uptake by thyroid gland and production of thyroid hormone Can be used to treat hyperthyroidism Not a problem when iodine intake is adequate Can cause or aggravate iodine deficiency when intake is marginal Found naturally in some foods: Cassava, maize, bamboo shoots, sweet potatoes, lima beans, and the Brassica group of vegetables. Cassava
Contains linamarin which is converted to thiocyanate Iodine and cretinism Inadequate iodine intake of the mother Marginal iodine intake of the mother and goiterogens Reduced synthesis of thryoid hormone T4 Inadequate T4 for production of active T3 Inadequate T3 available for developing fetus Inadequate T3 during critical period of brain development Severe mental retardation Inadequate T3 during critical period of cochlear development deafness ...
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This note was uploaded on 09/05/2009 for the course NTR Nutrition taught by Professor Meadows during the Spring '09 term at University of Texas.
- Spring '09