Pediatric Aspects of Thyroid Function and Iodine

Meyer Knobela, Geraldo Medeiros-Neto0

aThyroid Unit, Division of Endocrinology and Metabolism, Hospital das ClĂ­nicas, and bDepartment of Internal Medicine, University of Sao Paulo Medical School, Sao Paulo, Brazil

Iodine is a nonmetallic micronutrient present in the human body in minute amounts (15-20 mg), almost exclusively in the thyroid gland. It is an essential component of the thyroid hormones, thyroxine (T4) and triiodothyronine (T3), comprising 65 and 59% of their respective weights. Thyroid hormones, and therefore iodine, regulate many key biochemical reactions, especially protein synthesis and enzymatic activity. They also play a determining role in the process of early growth and development of most organs, especially that of the brain, which occurs in humans during the fetal and first 2-3 years of postnatal life. Consequently, iodine deficiency, if severe enough to affect thyroid hormone synthesis during this critical period, will result in hypothyroidism and brain damage. The clinical consequence will be irreversible mental retardation [1].

Iodine is found in relative abundance in marine plants and animals, in the thyroid gland of vertebrates, in deposits of organic origin, in certain natural mineral water, in sedimentary phosphate rock, and in association with certain mineral deposits. Most of the Earth's iodine is found in its oceans and most of the iodine ingested by humans comes from food of animal and plant origin. This iodine, in turn, is derived from the soil. In general, the older an exposed soil surface, the more likely the iodine has been leached away by erosion. Only a relatively small fraction is derived from drinking water. A most important factor in the depletion of iodine has been glaciation, which removes old soil and scrapes bare the virgin rocks, which have iodine concentrations far lower than those of the covering soil. This situation is found in regions that remained longest under Quaternary glaciers and lost their iodine when the ice thawed. Mountainous regions, such as those found in the Himalayas, the Andes, the Alps, Vietnam, China, Indonesia and Africa and also in flooded river valleys,

Table 1. Recommended iodine allowance (RDA) and urinary iodine concentration for different age groups (adapted from [6-8])

Life stage

Age

Estimated

Urinary iodine

Was this article helpful?

0 0

Post a comment