An assessment of iodine nutritional status and thyroid hormone levels in children aged 8-10 years living in Zhejiang Province, China: a cross-sectional study

Iodine is an essential nutrient for the synthesis of thyroid hormones that are critical for brain development. Iodine deficiencies were prevalent in China until the introduction of universal salt iodization (USI) in 1995. USI has been considered as the world's best achievements. This study aims to assess children's iodine nutrition and goiter status in Zhejiang Province in order to provide reasonable suggestions to the government for policy-making under the USI period. A cross-sectional survey in Zhejiang Province was conducted to children aged 8-10 years by stage cluster random sampling method. Spot urine samples were collected and analyzed. Thyroid ultrasonography examination was performed by special trained technicians using a 7.5-MHz transducer. Fasting venous blood samples were collected and analyzed for thyroid functional status. The median urinary iodine concentration was found to be 173.3 mu g/L. The percentage of urine samples with iodine concentration < 100 mu g/L, 100-300 mu g/L, and > 300 mu g/L was 15.5, 42.0, and 13.3 %, respectively. Goiter prevalence rate with iodine concentration < 100 mu g/L, 100-300 mu g/L, and > 300 mu g/L was 6.8, 10.0, and 14.9 %, respectively, with no significant difference. Children with goiter have lower serum FT3 and T3 concentrations compared to those without goiter (p < 0.05). Conclusions: The median urinary iodine concentration of children aged 8-10 years falls in optimal iodine status as recommended by WHO/UNICEF/ICCIDD. Maintaining USI at an appropriate level is an important part of preventing iodine deficiency disorders and should always be based on routine monitoring urinary iodine concentration by the province.