Saliva Iodine Concentration in Children and Its Association with Iodine Status and Thyroid Function

Context: The effectiveness of saliva iodine concentration (SIC) in evaluating iodine status in children is not clear. Objective: We aimed to explore associations between SIC and assessed indicators of iodine status and thyroid function. Design: Cross-sectional study. Setting: Primary schools in Shandong, China. Participants: Local children aged 8 to 13 years with no known thyroid disease were recruited to this study. Main outcome measures: Blood, saliva, and urine samples were collected to evaluate thyroid function and iodine status. Results: SIC positively correlated with spot urinary iodine concentration (r = 0.29, P < 0.0001), 24-hour urinary iodine concentration (r = 0.35, P < 0.0001), and 24-hour urinary iodine excretion (r = 0.40, P < 0.0001). The prevalence of thyroid nodules (TN) and goiter showed an upward trend with SIC quantiles (P for trend < 0.05). Children with SIC <105 mu g/L had a higher risk of insufficient iodine status (OR = 4.18; 95% CI, 2.67-6.56) compared with those with higher SIC. Those having SIC >273 mu g/L were associated with greater risks of TN (OR = 2.70; 95% CI, 1.38-5.26) and excessive iodine status (OR = 18.56; 95% CI, 5.66-60.91) than those with lower SIC values. Conclusions: There is a good correlation between SIC and urinary iodine concentrations. It is of significant reference value for the diagnosis of iodine deficiency with SIC of less than 105 mu g/L and for the diagnosis of iodine excess and TN with SIC of more than 273 mu g/L. Given the sanitary nature and convenience of saliva iodine collection, SIC is highly recommended as a good biomarker of recent iodine status in school-aged children.