Wanqi Zhang

Urinary iodine concentration (UIC) is influenced by variable urine volume, undermining its reliability. The urinary iodine/creatinine ratio (UI/Cr) may provide a more stable measure, especially in pregnancy. This study aimed to explore the variation of UI/Cr in assessing iodine status in pregnant women, and determine the sample size and optimal sampling time for accurate assessment. Thirteen pregnant women participated in a seven-day iodine metabolism study. All urine samples from each participant were collected separately over the 7-day period, and urinary iodine and urinary creatinine were tested. Spot UIC was positively correlated with time interval (β = 12.09, P < 0.001). UI/Cr, an indicator corrected for volume effect, showed no significant effect with time interval (β = -3.00, P = 0.090). The CV of UI/Cr was lower than UIC at both individual (56.16% vs. 73.15%) and population levels (62.41% vs. 84.75%). With a 95% confidence interval and ± 20% precision, an individual needs 33 urine samples, while a population requires 39 samples. The mixed-effects model analysis revealed that spot UI/Cr during the 18:00–23:59 period exhibited the strongest correlation with 24-hour UI/Cr (β = 0.62, P < 0.001). Additionally, spot UI/Cr during the 12:00–17:59 period demonstrated the strongest correlation with 24-hour urinary iodine excretion (β = 0.61, P < 0.001). The UI/Cr provides a more reliable estimate of iodine status than UIC. To obtain a precision of ± 20%, 33 spot-urine samples are required for individual assessment and 39 for population-level evaluation. We recommend urine collection between 12:00 and 18:00 for accurate evaluation.

Drinking water with a high iodine content is one of the sources of iodine intake, And excessive iodine intake can affect thyroid function. This study aims to investigate the effects of long-term exposure to iodine-rich groundwater on iodine intake And thyroid function in children. We recruited a total of 3,216 children aged 3–14 years on multiple occasions from 2013 to 2023 from counties with high groundwater iodine concentrations in Shandong Province, China. We collected drinking water samples to measure water iodine concentration (WIC), spot urine samples And 24-hour (24-h) urine samples to examine the iodine status. We measured the thyroid volume and collected fasting blood and dried blood spot samples to examine the thyroid function. The median WIC of children’s drinking water was 183 (IQR 70.0-362) µg/L. Within each age group, all iodine indicators, including urine iodine concentration And 24-hour urine iodine excretion, etc., and thyroid volume increased significantly with increasing water iodine concentration. The odds ratios (ORs) of the impact of drinking water with iodine concentration > 300 µg/L on hyperthyrotropinemia And goiter were 1.77 (95% confidence interval [CI], 1.20–2.62) And 4.19 (95% CI, 2.68–6.57), respectively. In children, prolonged exposure to an environment with high groundwater iodine content is associated with an increase in thyroid volume, a higher prevalence of goiter, and an increased risk of hyperthyrotropinemia. Continued efforts to reduce iodine concentration in drinking water are necessary.

Data on the distribution of iodine in the urine and breast milk of lactating women are limited. This study aimed to establish a formula to assess iodine status in lactating women by evaluating the fractional iodine excretion in urine and breast milk. A 3-d 24-h iodine metabolism survey in 2021–2023 was conducted on fifty-four pairs of lactating women and infants in Tianjin and Luoyang, China. We used the 24-h dietary record and salt weighing method to assess daily iodine intake (DII). Iodine excretion in breast milk and urine was measured. The median 24-h urinary iodine concentration and breast milk iodine concentration were 135·06 μg/L and 150·26 µg/L, respectively. When the DII was between 240 μg/d and 600 μg/d, the predicted value of fractional breast milk iodine excretion was 31·48 % (95 % CI: 27·16 %, 36·22 %). When the daily iodine excretion was between 258 μg/d and 476 μg/d, the fractional urine iodine excretion (59·09 %) and fractional breast milk iodine excretion (40·91 %) were stable. DII can be derived from the spot urinary iodine concentration as follows: urinary iodine concentration (μg/L) × (0·0009 L/h/kg × 24 h/d) × body weight (kg) ÷ 0·59 ÷ 0·94 = DII (μg/d). In conclusion, lactating women with adequate iodine delivered approximately 31·48 % of the DII to their infants. A stable proportion (59·09 %) of iodine excretion was discharged through urine, which was used to assess the iodine status based on the spot urinary iodine concentration of lactating women. This study was registered at ClinicalTrials.gov (NCT04492657).

Purpose There have been no reports on the application of salivary iodine concentration (SIC) in evaluating iodine nutrition in pregnant women. This study aimed to clarify the relationship between SIC and indicators of iodine nutritional status and thyroid function during pregnancy, to investigate whether salivary iodine can be applied to the evaluation of iodine nutritional status in pregnant women, and to provide a reference basis for establishing a normal range of salivary iodine values during pregnancy. Methods Pregnant women were enrolled in the Department of Obstetrics, the people’s hospital of Yuncheng Country, Shandong Province, from July 2021 to December 2022, using random cluster sampling. Saliva, urine, and blood samples were collected from pregnant women to assess iodine nutritional status, and venous blood was collected to determine thyroid function. Results A total of 609 pregnant women were included in this study. The median spot urinary iodine concentration (SUIC) was 261 μg/L. The median SIC was 297 μg/L. SIC was positively correlated with SUIC (r = 0.46, P < 0.0001), 24-h UIC (r = 0.30, P < 0.0001), 24-h urinary iodine excretion (24-h UIE) (r = 0.41, P < 0.0001), and estimated iodine intake (EII) (r = 0.52, P < 0.0001). After adjusting for confounders, there was a weak correlation between SIC and serum total iodine and serum non-protein-bound iodine (P = 0.02, P = 0.04, respectively). Pregnant women with a SIC < 176 μg/L had a higher risk of insufficient iodine status (OR = 2.07, 95% CI 1.35–3.19) and thyroid dysfunction (OR = 2.71, 95% CI 1.18–6.21) compared to those with higher SIC. Those having SIC > 529 μg/L were more likely to have excessive iodine status (OR = 2.82, 95% CI 1.81–4.38) and thyroid dysfunction (OR = 3.04, 95% CI 1.36–6.78) than those with lower SIC values. Conclusion SIC is associated with urinary iodine concentration and thyroid function in pregnant women. SIC < 176 μg/L was associated with an increased risk for iodine deficiency and hypothyroxinemia, while SIC > 529 μg/L was related to excess and thyrotoxicosis. SIC can be used as a reference indicator for evaluating the iodine nutrition status of pregnant women, but it needs further investigation and verification. Trial registration NCT04492657(Aug 9, 2022).