Exploration of Effects of Excessive Iodine on Children and Tolerable Upper Intake Level of Iodine for Children

With the implementation of Universal Salt Iodization (USI) in 1995, China has successfully combated Iodine Deficiency Diseases (IDD). However, China is a country with a complicated iodine geographical environment with wide natural variation in the iodine content of drinking water. It has been reported that the water iodine of at least 11 provinces and cities in China is high, with nearly 31 million people exposed to the risks of excessive iodine intake. This has raised a new public health concern that a safe upper level of iodine intake should be established to ensure that people avoid ingesting excessive iodine intake while continuing to implement USI to control IDD. The investigators have successfully explored the tolerable upper intake level (UL) of iodine for Chinese adults by conducting a randomized double-blinded trial in 256 euthyroid volunteers. However, due to limited data on the safe upper intake level of iodine for children worldwide, current ULs of iodine for children are extrapolated from those for adults based on body weight or body surface area. As it is impossible to ethically conduct a randomized clinical trial regarding excessive iodine intake in children, the investigators plan an observational study to investigate children who have been living with different drinking water iodine levels for over 5 years, observing the changes of thyroid function in response to each iodine exposure level. Subtle changes in thyroid function and thyroid volume of children corresponding to different iodine intake levels will be determined, which will contribute to the establishment of UL of iodine for children. The aim was: 1. To establish the tolerable upper intake level (UL) of iodine for children of China. 2. To define the adverse effects of excess iodine on children. 3. To monitor the iodine status of children living in high water iodine areas in China.