**1. Introduction**

Thyroxine (T4) and 3,5,3′-triiodothyronine (T3) are the two thyroid hormones, each of them containing two iodine atoms on their inner (tyrosine) ring. The difference between them is that T3 has only one iodine atom on its outer (phenyl) ring, whereas T4 has two. Synthesis of reasonable quantities of thyroid hormones requires adequate iodine intake to allow sufficient thyroidal uptake. The World Health Organization (WHO) recommendation for daily intake of iodine is 90 μg for infants and children up to 5 years, 120 μg for children 6–12 years, 150 μg for children ≥12 years and adults, and 250 μg for pregnant and lactating women [1]. The worldwide variability of the dietary intake of iodine depends on the iodine content of the soil, water, and the dietary practice. After Iodine Global Network data [2], the iodine uptake in Romania in 2004 was considered adequate, the median urinary iodine content (MUIC, normal value ≥100 μg/L) being 102 μg/L in school-aged children, but in some geographic regions, such as mountainous villages of Mureș County, a mild iodine deficiency was detected [3]. The MUIC value (68 μg/L) in

pregnant women confirmed that iodine intake in this population of Romania is insufficient [2]. Administration of supplemental iodine to subjects with iodine deficiency goiter can result in iodine-induced hyperthyroidism in nonpregnant persons [4], but iodine supplementation in mild and moderate iodine-deficient pregnant women lowers thyroid hormone level [5].
