The purpose of this study was to research the factors influencing thyroid volume (TVOL) in 6∼12-year-old children and update the reference values. A cross-sectional study was carried out in iodine-sufficient areas of four provinces in China. Urine, edible salt, and drinking water samples were collected from children. Children’s height, weight, and TVOL were measured. Ridge regression was used to screen variables for solving the multicollinearity problem. Quantile regression was used to analyze the relationship between the quantiles of TVOL and other variables. In total, 5653 children aged 6∼12 years were enrolled in this study, including 2838 boys and 2815 girls. There was no significant difference in TVOL between boys and girls (P>0.05). Spearman correlation analysis showed that total TVOL was positively correlated with age, height, weight, BSA and BMI, and the correlation coefficients were 0.614, 0.625, 0.646, 0.653 and 0.488 respectively. Among them, the correlation between TVOL and BSA was the strongest. According to the ridge regression results, age and body surface area (BSA) influenced TVOL, and the ridge regression coefficients were 0.13 and 0.94 respectively. Quantile regression further showed that age and BSA had significant influences on the whole TVOL distribution (P<0.001). Therefore, the TVOL of children aged 6∼12 years in China was mainly influenced by age and BSA, and reference values for TVOL of different genders based on age and BSA were established.

Excessive iodine can lead to goiters. However, the relationship between the water iodine concentration (WIC) and goiter rate (GR) is unclear. This study aims to explore the factors that influence children’s GR in areas with high WIC and analyse the threshold value of the GR increase associated with the WIC. According to the monitoring of the areas with high WIC in China in 2018–2020, a total of 54,050 children in eight high water iodine provinces were chosen. Drinking water, urine and edible salt samples of children were collected. The thyroid volume (Tvol) was measured. A generalized additive model (GAM) was used to analyse the relationship between the WIC and GR in children. Among the 54,050 children in areas with high WIC, the overall GR was 3.34%, the median of water iodine concentration (MWIC) was 127.0 µg/L, the median of urinary iodine concentration (MUIC) was 318 µg/L, and the noniodized salt coverage rate (NISCR) was 63.51%. According to the GAM analysis results, water iodine and urinary iodine are factors that influence the Tvol and GR, while the NISCR affects only the GR. When the WIC was more than 420 µg/L or the urinary iodine concentration (UIC) was more than 800 µg/L, the GR increased rapidly. When the NISCR reached more than 85%, the GR was the lowest. Thus, in areas with high WIC, WIC more than 420µg/L may increase the risk of goiter, and the NISCR should be increased to over 85% to avoid goiters in children.