Appropriate Range of Median Urinary Iodine Concentration in 8- to 10-Year-Old Children Based on Generalized Additive Model.

ABSTRACT

Background: The appropriate range of median urinary iodine concentration (MUI) in children has always been controversial. To prevent the occurrence of a goiter epidemic in Shanghai, we explored the appropriate range of MUI by integrating multiple monitoring results. Methods: This study summarized and analyzed the monitoring data from 1997, 1999, 2011, 2014, and 2017 of children living in Shanghai. In each monitoring year, the probability-proportional-to-size sampling technique was used to select 30 sampling units. In each sampling unit, one primary school was randomly selected. From each selected school, 40 children 8- to 10-year-old were randomly recruited to measure thyroid volume (Tvol) and their household salt iodine intake. Results: In 1997, 1999, 2011, 2014, and 2017, MUI of 8- to 10-year-old children was 228, 214, 182, 171, and 183 µg/L, and median Tvol (MTvol) was 2.9, 1.2, 1.0, 1.8, and 2.8 mL, respectively. There was a linear correlation between goiter rate and MTvol (r = 0.95, p = 0.014; 100 × goiter rate = 1.314 × MTvol -1.287). Generalized additive model (GAM) was used to predict MTvol as follows, MTvol = 0.60689 + 0.00302 MUI +0.999928 s (MUI) -0.05172 mean salt iodized concentrations (MSIs) +0.03481 × 100 × iodized salt coverage rate +0.00000969 per capita disposable income +0.271422 s (per capita disposable income) -0.38772 × monitoring year gap. The results revealed that the average relative error between predicted and actual value was 15.2%. GAM results showed that at 27-277 µg/L MUI, the goiter rate was <5%. Conclusions: Iodine status is appropriate in Shanghai. Under the existing economy and MSI, the optimal range of MUI should be 70-277 µg/L in 8- to 10-year-old children living in Shanghai.