The thyroid gland alone consumes almost seventy-five percent of iodine in the body. As the top plot shows, daily recommended dose of iodine depends on your age and condition, e.g., pregnancy and breastfeeding may require a lot more.
Thyroid produces two hormones: T4 (thyroxine) with four iodine atoms, and T3 (tri-iodo-thyronine) with three iodine atoms.
Whenever necessary, T4 in the blood converts to a more active T3 hormone by releasing one iodine atom. Maintaining body temperature during cold is such an example of iodine exchange: First, on exposure to cold, T4 in the blood converts to T3. Then, thyroid receptors around lever, heart, kidneys and other vital organs initiate the process of burning the body fat to raise the body temperature.
Despite the small size, thyroid gland produces some of the most important hormones necessary for a baby during pregnancy. Therefore, adequate supply of iodine is extremely important for the development of infants. Research has shown a strong correlation between T4 levels of mothers and the IQ of babies after they grow into adults. Therefore, insufficient iodine use during pregnancy can lead to long-term impact on society with poor intellectual abilities.
Iodine is commonly found in seafoods. Therefore, coastal regions tend to have excess supply. On the other hand, regions further inland, with limited access to seafoods, tend to be iodine deficient. To meet the daily iodine requirement, salt is often fortified with iodine and sold as iodized salt.
This approach of adding iodine to salt has been very successful in reducing mental disorders in newborn babies in developing countries that historically lacked iodine in their diets. It has also helped reduce cases of goiter—which appears as a swollen neck when the thyroid gland enlarges in order to produce adequate levels of T3 and T4. Insufficient iodine is one of the most common causes of goiter apart from thyroid dysfunction.
Adequate supply of iodine is important for maintaining a tightly controlled range of thyroid hormones. Whenever T3 and T4 levels aren’t optimal, e.g., during insufficient iodine supply, very opposite symptoms are observed and the condition is termed hypothyroidism. Typical signs include high sensitivity to cold, weight gain and slow response.
Although excess iodine eventually leaves the body via urine, over long periods it can result in high levels of thyroid hormones causing hyperthyroidism. Commonly observed symptoms of hyperthyroidism include hyperactivity, with a faster metabolism and constant feeling of being hungry. A more visible sign is the intolerance to heat, accompanied with other symptoms including anxiety, nervousness, sweating, weakness of muscles, and heart palpitations.
Another related key hormone released by the pituitary gland in our brain is called TSH (thyroid stimulating hormone). TSH is the main switch that balances adequate thyroid hormone levels. In case of thyroid dysfunction, TSH levels drive the gland to compensate for excess or low T3 and T4—until a certain level. Once this subclinical threshold is reached, an overt hypothyroidism or overt hyperthyroidism might require immediate medical attention. Beside inadequate supply of iodine, age and pregnancy can also throw off this delicate balance maintained by TSH.
In rare cases, the body’s immune system starts to attack thyroid gland—often due to an auto-immune disease. Also called, Hashimoto's autoimmune thyroiditis, excess production of antibodies called TPO (thyroid peroxidase) can be detected with a comprehensive thyroid blood test. The test checks for free-T3, free-T4, TSH and TPO antibodies. Regular testing is an excellent way to ensure people consume healthy amount of iodine in their diet.
Graves's thyroid disease is another autoimmune disorder in which the body produces too much thyroid hormones. In some cases, it leads to bulging puffy red eyes resulting in thyroid eye disease or Graves's ophthalmopathy. A thyroid stimulating hormone test should help assess the abnormal TSH and T4, T3 levels. You may sometimes require additional tests to check for thyroid stimulating immunoglobulin (TSI), which are another type of antibodies that behave similar to TSH causing the thyroid gland to overproduce T4, T3 hormones.
Order a Thyroid Stimulating Hormone Test.
All About Thyroid - an in depth summary of thyroid gland, hormones, and disorders.
Normal TSH Levels: What's Normal and Why? - a detailed look at thyroid stimulating hormone.
5 Signs You Should Take an At-Home Thyroid Test - key symptoms that suggest it's time to get tested.
The Difference Between Hypothyroidism and Hyperthyroidism - a quick look at key differences.
Tips For Understanding Your Home Thyroid Results - a few tips on understanding your results.
Thyroid in Pregnancy - what research says about the critical role of thyroid during pregnancy.
Thyroid and Iodine - thyroid problems are highly dependent on too little or too much iodine.
