A study on the differences in urinary iodine and serum iodine in relation to 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. Nonetheless, the connection between iodine nutritional status and childhood dyslipidemia remains unclear. This study examined 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) and triglyceride (TG) was explored using kernel density plots and chi-square tests. The logistic regression model incorporated covariates (age, sex, BMI) to control for potential confounding factors and examined the relationship between UIC, SIC, and lipid profile; meanwhile, stratified analysis and interaction analysis were conducted to test the effect modification of these variables on the aforementioned associations. Restricted cubic splines models based on logistic regression were utilized to examine dose-response relationships involving 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 linked with elevated TC [OR 1.455 (1.175–1.802)]. 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 [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 linked to a higher likelihood of hypertriglyceridemia, exhibiting a non-linear relationship.