Iodine status of school-aged children in the changing context of universal salt iodization program during 1997-2018 in Chongqing, China

Objective: To illustrate the changes of iodized salt usage, goiter rate of school-aged children and median urinary iodine concentration (MUIC) of school-aged children in Chongqing for the last 21 years. This study aims to estimate the variational provincial status of iodine nutrition and provide scientific evidence for fine-tuning and adaptation of the current program.Methods: Different number of families and school children aged 8-10 years from Chongqing during 1997-2018 participated in the study. UIC and iodine content in table salt were measured. Thyroid volumes of students were examined and goiter prevalence was calculated across years.Results: The median iodine content of table salt was negatively associated with years(r =-0.727, P < 0.01). The MUIC were decreased annually (ranged between 200 and 300 mu g/L) and was negatively associated with year(r =-0.831, P < 0.01). Goiter of school-aged children in Chongqing was decreased from the highest rate of 23.58% in 1999 to 1.62% in 2018(Cochran-Armitage Trend Test: chi(2)=-30.695, P < 0.01). Thyroid volume were negatively associated with years(r =-0.962, P < 0.01) and had a positive relationship with MUIC 1997-2018 (r = 0.862, P < 0.01).Conclusions: The consumption of adequately iodized salt can eliminate Iodine deficiency disorders (IDD) in children, but possible excessive iodine intake from salt could result in high urinary iodine excretion and even goiter. A systematic, well-designed and continual program monitoring is essential to ensure the adequacy of iodine fortification levels and to regularly change the iodine concentration in household table salt.