A Study on the Differences in Urinary Iodine and Serum Iodine in Revealing the Relationship between Children's Iodine Nutrition and Lipids

The safe intake range for iodine is narrow, and abnormal nutritional status (deficiency or excess) may affect children's lipid metabolism by interfering with thyroid function. Following the widespread implementation of iodized salt in China, urinary iodine levels in children in some regions have exceeded the appropriate range. However, the relationship between iodine nutritional status and childhood dyslipidemia remains unclear. This study investigated the associations between iodine status and lipid profiles among 6–17-year-old children and adolescents residing in regions of China where iodized salt is supplemented. The correlation between urinary iodine concentration (UIC), serum iodine concentration (SIC), and total cholesterol (TC), triglyceride (TG) were analyzed using kernel density plots and chi-square tests. Logistic regression models explored the relationship between UIC, SIC, and lipid profiles, while the effects of potential confounding factors were examined through stratified and interaction analyses. Restricted cubic splines models based on logistic regression were used to characterize dose–response associations between UIC, SIC and dyslipidemia. The results revealed that hypertriglyceridemia followed a U-shaped pattern across UIC groups, whereas hypercholesterolemia rose steadily with increasing UIC. Both outcomes showed U-shaped associations with SIC. After adjustment, UIC ≥ 300 µg/L was positively associated with elevated TC [OR 1.455 (1.175–1.802)], and FT3 plays a certain mediating role in the process by which excessive urinary iodine affects total cholesterol (TC) levels. Elevated TG was also more likely when the SIC was < 63.50 µg/L [OR 1.305 (1.022–1.665)] or ≥ 82.28 µg/L [OR 1.536 (1.204–1.960)]. SIC is in a U-relationship with TG levels, whereas SIC values > 74.66 µg/L appeared to interact synergistically with TG. In conclusion, high urinary iodine is a risk factor for hypercholesterolemia, but this association is modified by BMI. Both low serum iodine and high serum iodine are associated with an increased risk of hypertriglyceridemia, exhibiting a non-linear relationship. Keywords: Adolescents, Children, Dyslipidemia, Iodine exposure