The primary function of iodine is to enable the synthesis of the thyroid hormones thyroxine and triiodothyronine, otherwise known as T3 and T4, respectively. T4 exists in the blood in much greater quantities than T3, yet it is T3, the metabolically active thyroid hormone, which is far more significant biologically. Much of the T4 (which contains 4 iodine atoms per molecule) is actually converted into T3 (which contains 3 iodine atoms per molecule), both in the thyroid gland itself and in other parts of the body such as the liver, skeletal muscles, and brain. However, if the cells are still not getting enough T3, a thyroid-stimulating hormone, known as TSH, is secreted by the pituitary gland in an attempt to get the thyroid gland to produce more. While the process is very complicated and many things can disrupt it, apart from iodine deficiency, adequate iodine intake is a key factor.
The body requires T3 to regulate the metabolic rate, provide energy, and facilitate growth. However, there is also much more that this thyroid hormone does. Although the thyroid hormones are often thought of only in connection with their role in metabolism, their far-reaching effect extends to virtually every aspect of body functioning. That makes the importance of iodine, without which thyroid hormone production would cease, equally far reaching.
The brain, heart, and muscles, for example, all depend on T3—and iodine—to work properly. A prolonged severe state of iodine deficiency can not only cause severe and sometimes irreparable damage, but even be life threatening.
Iodine is necessary for a healthy pregnancy and normal fetal development, and adequate intake throughout pregnancy will greatly reduce the likelihood of preventable miscarriages or babies with low birth weight and serious birth defects.
Iodine is essential to healthy neurological development, not only in infancy, but throughout life. In addition to the high incidence of mental retardation in babies born to iodine deficient mothers, many other serious medical conditions have been linked to iodine deficiency, including multiple sclerosis, Alzheimer’s disease, Parkinson’s disease, and other diseases of the nervous system. Iodine is also needed for the immune system to operate effectively.