Serum Iodine Is Correlated with Iodine Intake and Thyroid Function in School-Age Children from a Sufficient-to-Excessive Iodine Intake Area

Abstract

Background An alternative feasible and convenient method of assessing iodine intake is needed. Objective The aim of this study was to examine the utility of serum iodine for assessing iodine intake in children. Methods One blood sample and 2 repeated 24-h urine samples (1-mo interval) were collected from school-age children in Shandong, China. Serum free triiodothyronine (FT3), free thyroxine (FT4), thyroid-stimulating hormone (TSH), thyroglobulin (Tg), total iodine (StI), and non-protein-bound iodine (SnbI) concentrations and urine iodine (UIC) and creatinine (UCr) concentrations were measured. Iodine intake was estimated based on two 24-h urine iodine excretions (24-h UIE). Associations between serum iodine and other factors were analyzed using the Spearman rank correlation test. Receiver operating characteristic (ROC) curves were used to illustrate diagnostic ability of StI and SnbI. Results In total, 1686 children aged 7–14 y were enrolled. The median 24-h UIC for the 2 collections was 385 and 399 μg/L, respectively. The median iodine intake was estimated to be 299 μg/d and was significantly higher in boys than in girls (316 μg/d compared with 283 μg/d; P < 0.001). StI and SnbI were both positively correlated with FT4 (ρ = 0.30, P < 0.001; and ρ = 0.21, P < 0.001), Tg (ρ = 0.21, P < 0.001; and ρ = 0.19, P < 0.001), 24-h UIC (ρ = 0.56, P < 0.001; and ρ = 0.47, P < 0.001), 24-h UIE (ρ = 0.46, P < 0.001; and ρ = 0.49, P < 0.001), urine iodine-to-creatinine ratio (ρ = 0.58, P < 0.001; and ρ = 0.62, P < 0.001), and iodine intake (ρ = 0.49, P < 0.001; and ρ = 0.53, P < 0.001). The areas under the ROC curves for StI and SnbI for the diagnosis of excessive iodine intake in children were 0.76 and 0.77, respectively. The optimal StI and SnbI threshold values for defining iodine excess in children were 101 and 56.2 μg/L, respectively. Conclusions Serum iodine was positively correlated with iodine intake and the serum FT4 concentration in children. It is a potential biomarker for diagnosing excessive iodine intake in children. This trial was registered at clinicaltrials.gov as NCT02915536.

Iodine intake in healthy Japanese aged from 6 to 70 years residing in the same district

“…In our subjects UI/Cr tended to increase with age and higher estimated 24-h UIE adjusted by predicted Cr excretion was observed in elderly adults as well as in male subjects, while there were no significant differences of median UIC, UI/Cr and DII between males and females. This gender-related difference of UIE was partially inconsistent with the previous reports [26,29]; however, in a large epidemiological study of 3,350 university students (18-22 years, M/F ratio, 1: 0.73) residing in Kobe, Japan, there was no difference in the median UIC values in spot urine samples by gender [30]. The gender difference of iodine excretion is still in controversy.…”

The Joint Role of Iodine Status and Thyroid Function on Risk for Preeclampsia in Finnish Women: a Population-Based Nested Case-Control Study

“…Third, the samples we analyzed were taken between 10 and 14 weeks gestation, a key period in the development of preeclampsia. Finally, we measured iodide levels in serum, which recent research suggests may be more reliable and less subject to fluctuation than urinary iodine [23][24][25]. In one study serum iodine concentrations were significantly (p 0.002 to 0.007) correlated with thyroid stimulating hormone and free T3 and free T4 concentrations in hypothyroid patients.…”

The Joint Role of Thyroid Function and Iodine Status on Risk of Preterm Birth and Small for Gestational Age: A Population-Based Nested Case-Control Study of Finnish Women

“…Because of this, UIC is considered an acceptable biomarker of iodine status for whole populations, but not for individuals [35]. Serum iodine on the other hand, is less sensitive to recent dietary intake and may better reflect individual iodine status over longer periods of time [19], possibly reducing misclassification of exposure.…”

“…Additionally, prior studies used a single spot urinary iodine measurement to classify iodine status, which has been shown to have high intraindividual variability reflective of recent dietary intake, seasonal variation, urine dilution, and circadian rhythmicity [13,14,15,16]. Although urine iodine concentrations are useful for assessing the iodine status of whole populations, serum iodide may be less sensitive to recent dietary intake and may, therefore, better reflect individual long-term and bioavailable iodine status [17,18,19], reducing potential for misclassification.…”