The impact of removing iodised salt on children's goitre status in a high-iodine area (HIA) remains unclear. The aim of the present study was to explore the changes in the prevalence of goitre in children after removing iodised salt from their diet. For this purpose, three towns with the median water iodine content of 150–300 μg/l were selected randomly in Hengshui City, Hebei Province, China. A total of 452 and 459 children were randomly selected from the three towns in order to measure thyroid volume by ultrasound before and after removing iodised salt, respectively. Their goitre status was judged using the criteria of age-specific thyroid volume recommended by the WHO. After removing iodised salt, the overall median urinary iodine content (MUIC) of children decreased from 518 (interquartile range (IQR) 347–735) to 416 (IQR 274–609) μg/l. The MUIC of children across sex and age group decreased significantly except for the age group of 9 years. The overall prevalence of goitre in the three towns significantly decreased from 24·56 % (n 111/452) to 5·88 % (n 27/459) (P< 0·001). Goitre prevalence in children aged 8–10 years decreased from 33·70 % (n 31/92), 23·32 % (n 45/193) and 20·96 % (n 35/167) to 6·10 % (n 10/164), 5·52 % (n 9/163) and 6·06 % (n 8/132), respectively. Goitre prevalence in boys and girls decreased from 27·05 % (n 66/244) and 21·63 % (n 45/208) to 6·66 % (n 15/226) and 5·15 % (n 12/233), respectively. The decreases in the prevalence of goitre in children across sex and age group were all statistically significant. The present study revealed that goitre prevalence in children decreased significantly after removing iodised salt from their diet for about 1·5 years in the HIA in Hebei Province.

The prevalence of goitre in areas with mildly excessive iodine in drinking-water is still under debate. The aim of the present study was to explore the prevalence of goitre and its epidemiological characteristics in these areas using WHO criteria. To this end, three towns with a median water iodine (MWI) of 150–300 μg/l were selected randomly in Hengshui City of Hebei Province of China, and one town with a MWI of 105 μg/l was chosen as a control. A total of 452 children in the three towns and 120 children in the control town were randomly selected to measure thyroid volume (Tvol) by ultrasound. The goitre status of these children was judged using the criteria recommended by the WHO. The overall goitre prevalences in the three towns were 24·6 % (111/452) by age-specific Tvol and 33·0 % (149/452) by body surface area (BSA)-adjusted Tvol, which were significantly higher than that in the control town by both age-specific Tvol (14·0 % (17/120), P= 0·015) and BSA-adjusted Tvol (17·5 % (21/120), P= 0·001). Significant differences were found neither in goitre prevalences across sex by both age-specific Tvol (P= 0·078) and BSA-adjusted Tvol (P= 0·692) nor in that across age group by both BSA-adjusted Tvol (P= 0·461) and age-specific Tvol (P= 0·183). The present study found a high prevalence of goitre in children living in areas with mildly excessive iodine in drinking-water in Hebei Province. No significant differences were found in goitre prevalences across sex and age group. These results suggest that the Tvol reference values recommended by the WHO could be too low for Chinese children.

Excessive iodine intake can cause thyroid function disorders as can be caused by iodine deficiency. There are many people residing in areas with high iodine levels in drinking-water in China. The main aim of the present study was to map the geographical distribution of drinking-water with high iodine level in China and to determine the relationship between high iodine level in drinking-water and goitre prevalence. Iodine in drinking-water was measured in 1978 towns of eleven provinces in China, with a total of 28 857 water samples. We randomly selected children of 8–10 years old, examined the presence of goitre and measured their urinary iodine in 299 towns of nine provinces. Of the 1978 towns studied, 488 had iodine levels between 150 and 300 μg/l in drinking-water, and in 246 towns, the iodine level was >300 μg/l. These towns are mainly distributed along the original Yellow River flood areas, the second largest river in China. Of the 56 751 children examined, goitre prevalence was 6·3 % in the areas with drinking-water iodine levels of 150–300 μg/l and 11·0 % in the areas with drinking-water iodine >300 μg/l. Goitre prevalence increased with water and urinary iodine levels. For children with urinary iodine >1500 μg/l, goitre prevalence was 3·69 times higher than that for those with urinary iodine levels of 100–199 μg/l. The present study suggests that drinking-water with high iodine levels is distributed in eleven provinces of China. Goitre becomes more prevalent with the increase in iodine level in drinking-water. Therefore, it becomes important to prevent goitre through stopping the provision of iodised salt and providing normal drinking-water iodine through pipelines in these areas in China.