The hormone, which excites the nervous system and leads to increased activity of the endocrine system, remains active in the body for more than a month. Thyroxine plays an important role in childhood development, metabolism regulation, and breaking down fats and proteins.
This final act in thyroid hormone synthesis proceeds in the following steps).
Sources of Iodine Food Seaweed (such as kelp, nori, kombu, and wakame) is one of the best food sources of iodine, but it is highly variable in its content (Table 2) 5.
Thyroid function is primarily regulated by thyroid-stimulating hormone (TSH also known as thyrotropin. It is secreted by the pituitary gland to control thyroid hormone production and secretion, thereby protecting the body from hypothyroidism and hyperthyroidism 1.
Adequate Intake (AI established when evidence is insufficient to develop an RDA and is set at a level assumed to ensure nutritional adequacy. Estimated Average Requirement (EAR average daily level of intake estimated to meet the requirements of 50 of healthy individuals.
The iodine content of different seaweed species also varies greatly 11. For these reasons, the values in Table 2 are approximate. Table 2: Selected Food Sources of Iodine 10, 11, 12 Food Approximate Micrograms (mcg) per serving Percent DV Seaweed, whole or sheet, 1 g 16 to 2,984 11 to 1,989 Cod, baked, 3 ounces.
Iodine concentrations in plant foods can range from as little as 10 mcg/kg to 1 mg/kg dry weight 5. This variability in turn affects the iodine content of meat and animal products because it affects the iodine content of foods that the animals consume 10.
The iodine-replete healthy adult has about 1520 mg of iodine, 7080 of which is contained in the thyroid 6. Median urinary iodine concentrations of 100199 mcg/L in children and adults, 150249 mcg/L in pregnant women and 100 mcg/L in lactating women indicate iodine intakes are adequate 3.
However, the FDA does not require food labels to list iodine content unless a food has been fortified with this nutrient. Foods providing 20 or more of the DV are considered to be high sources of a nutrient.
These intakes meet or exceed the EAR for all groups. TDS data do not include iodine that people obtain from the discretionary use of iodized salt 16, 17. Because many U.S.
Thyroid peroxidase catalyzes two sequential reactions: Iodination of tyrosines on thyroglobulin (also known as "organification of iodide. Synthesis of thyroxine or triiodothyronine from two iodotyrosines. Through the action of thyroid peroxidase, thyroid hormones accumulate in colloid, on the surface of thyroid epithelial cells.
The earth's soils contain varying amounts of iodine, which in turn affects the iodine content of crops. In some regions of the world, iodine-deficient soils are common, increasing the risk of iodine deficiency among people who consume foods primarily from those areas.
Thyroid hormones regulate many important biochemical reactions, including protein synthesis and enzymatic activity, and are critical determinants of metabolic activity 1, 2. They are also required for proper skeletal and central nervous system development in fetuses and infants 1.
Salt iodization programs, which many countries have implemented, have dramatically reduced the prevalence of iodine deficiency worldwide 2, 3. Iodine in food and iodized salt is present in several chemical forms including sodium and potassium salts, inorganic iodine (I2 iodate, and iodide, the reduced form of iodine 4.
A molecule of thyroglobulin contains 134 tyrosines, although only a handful of these are actually used to synthesize T4 and T3. Iodine, or more accurately iodide (I- is avidly taken up from blood by thyroid epithelial cells, which have on their outer plasma membrane a sodium-iodide symporter or " iodine trap ".
Table 1: Recommended Dietary Allowances (RDAs) for Iodine 2 Age Male Female Pregnancy Lactation Birth to 6 months 110 mcg 110 mcg 712 months 130 mcg 130 mcg 13 years 90 mcg 90 mcg 48 years 90 mcg 90 mcg 913 years 120 mcg 1 years 150 mcg 150 mcg 220 mcg 290 mcg 19.
In the United States, salt manufacturers have been adding iodine to table salt since the 1920s, although it is still a voluntary program 12. The U.S. Food and Drug Administration (FDA) has approved potassium iodide and cuprous iodide for salt iodization 14 while the WHO recommends the use of potassium iodate due to its greater.
It is usually used to assess the adequacy of nutrient intakes in populations but not individuals. Tolerable Upper Intake Level (UL maximum daily intake unlikely to cause adverse health effects 2.
The protein thyroglobulin serves as a scaffold for thyroid hormone synthesis. Tyrosine residues in thyroglobulin are iodinated to form monoiodotyrosine (MIT) or diiodotyrosine (DIT) in a process known as iodineorganification. Within thyroglobulin, 2 molecules of DIT combine to form T4, while 1 molecule each of MIT and DIT combine to form T3.
Remember that hormone is still tied up in molecules of thyroglobulin - the task remaining is to liberate it from the scaffold and secrete free hormone into blood. Thyroid hormones are excised from their thyroglobulin scaffold by digestion in lysosomes of thyroid epithelial cells.
Thyroxine is taken to replace the deficiency which exists in such situations and therefore to restore normal metabolic activity. In humans, children born with thyroid hormone deficiency will not grow well, and brain development can be severely impaired, in the condition referred to as cretinism.