Relationship between water iodine, urinary iodine and thyroid volume of children in high water-iodine areas

Abstract

Objective To detect water iodine content, urinary iodine content and thyroid volume of children aged 6 -12 in high water-iodine areas and to explore the relationship between thyroid volume and the three factors (water iodine content, urinary iodine content and age). Methods In July 2011 to March 2012, four provinces of Shandong, Shanxi, Henan and Hebei were investigated, and water iodine content were divided into 4 levels, which were 50 -99, 100 -149, 150 -299, and ≥300 μg/L, respectively. For each water iodine content level, three villages were analyzed. School children aged 6 -12 were recruited, family salt iodine was determined to exclude those children who had intaken iodized salt. After that, water iodine content, urinary iodine content and thyroid volume of children were measured. Finally, relationships between thyroid volume and water iodine content, urinary iodine content and age were analyzed. Salt iodine was detected by semi-quantitative method; urinary iodine was detected by arsenic cerium catalytic spectrophotometry; thyroid volume was detected by B-scan ultrasonography. Results The medians of thyroid volume in each age group from 6 to 12 years were 2.00, 2.21, 2.54, 2.94, 3.30, 3.44, and 3.72 ml, respectively; the medians of urinary iodine content in each age group were 252.3, 319.4, 345.2, 350.9, 371.2, 384.4, and 409.6 μg/L, respectively. Under the condition of water iodine content > 100 μg/L, the median of urinary iodine content of children aged 6 in 100 -149 μg/L water iodine content group was 274.0 μg/L, while other groups with different ages got the median of urinary iodine content more than 300 μg/L. Water iodine content, urinary iodine content and age were all positively correlated with thyroid volume (r = 0.154, 0.148, 0.381, all P < 0.01). In addition, water iodine content and urinary iodine content were positively correlated (r = 0.399, P < 0.05). With the same water iodine content level, the urinary iodine content and thyroid volume showed a significant dispersion with increasing age, which meant different individual responses to higher iodine. Conclusions In higher water-iodine areas, the iodine level of children is excessive, although they have intaken non-iodized salt. Furthermore, thyroid volume is associated with water iodine content, urinary iodine content and age. Key words: Water; Urine; Iodine; Child; Thyroid