Associations between iodine intake, thyroid volume, and goiter rate in school-aged Chinese children from areas with high iodine drinking water concentrations

Abstract

Background: Excessive iodine intake may have adverse effects on the thyroid, particularly in children, but the safe upper iodine intake concentration in children is unclear. Objective: We assessed the adverse effects of high iodine intake from iodine-rich drinking water on thyroid size in children by examining associations between thyroid volume (Tvol), total goiter rate (TGR), and iodine intake. Design: In a multistage cross-sectional survey, we collected two 24-h urine samples on 2 nonconsecutive days and determined 24-h urinary iodine excretion, then calculated habitual daily iodine intake. Ultrasonographic Tvol was measured, and TGR was calculated based on international and Chinese reference ranges for Tvol in children.Results: This study included 2089 children from Shandong province, where the median (IQR) drinking water iodine concentration was 183 mg/L (69-406 mg/L). The median (IQR) 24-h urinary iodine concentrations for the 2 collections were 381 mg/L (203-649 mg/L) and 398 mg/L (202-687 mg/L), respectively. The median (IQR) habitual daily iodine intake of children was 298 mg/d (186-437 mg/d). Tvols were slightly higher in boys than in girls (P = 0.035). The overall TGR was 9.7% and did not differ by sex. The TGR was w5% for children aged 7-10 and 11-14 y at iodine intakes of 200-249 and 250-299 mg/d, respectively. With the use of logistic regression and 2-step linear regression, a nonlinear association was observed between Tvol, TGR, and iodine intake, with a threshold intake of 150 mg/d. Conclusions: Tvol begins to increase in children when iodine intake is $150 mg/d, and the TGR exceeds 5% when daily iodine intake is $250 mg/d for children aged 7-10 y and $300 mg/d for children aged 11-14 y. Our findings suggest that 150-249 and 150-299 mg/d seem to be safe upper iodine intake ranges for children aged 7-10 and 11-14 y, respectively. This trial was registered at clinicaltrials.gov as NCT02915536.Am J Clin Nutr 2017;105:228-33.

Excess iodine intake: sources, assessment, and effects on thyroid function

“…128 Data from China from areas with excessive iodine exposure due to iodine-concentrated potable water suggest that Tvol increases from an iodine intake in schoolchildren >150 g/day. 129 In another recent study in Chinese school-children, the odds ratio (OR) for total goiter rate per 50 g iodine intake increments rose from 0.9 (95% CI: 0.2-3.9) at an estimated daily iodide intake of 150-199 g, to 14.2 (95% CI: 4.8-42.7) at >600 g iodine/day. 56 A recent meta-analysis that compiled data from 43 Chinese studies, grouped them by iodine status, found a lower prevalence of thyroid nodules in the excessive iodine intake group compared with those with adequate or deficient intakes (7%, 25%, and 22%, respectively).…”

“…In a multicountry study, Tvol increased in school‐age children when iodine intakes were more than twice those recommended, equivalent to mUIC ≥ 500 μg/L . Data from China from areas with excessive iodine exposure due to iodine‐concentrated potable water suggest that Tvol increases from an iodine intake in schoolchildren >150 μg/day . In another recent study in Chinese school‐children, the odds ratio (OR) for total goiter rate per 50 μg iodine intake increments rose from 0.9 (95% CI: 0.2–3.9) at an estimated daily iodide intake of 150–199 μg, to 14.2 (95% CI: 4.8–42.7) at >600 μg iodine/day .…”

Eliminating Iodine Deficiency in China: Achievements, Challenges and Global Implications

“…Other studies, including in China, also suggest that goiter and thyroid hormone abnormalities seldom occur unless urinary iodine levels exceed 300 μg/L or higher [47,48,49,50,51]. A recently released Chinese study found no evidence of increased thyroid volume in iodine concentrations of 150–249 μg/L and 150–299 μg/L in 7–10- and 11–14-year-old children, respectively [52]. If the range of 100–299 μg/L were adopted by the global community as the optimal range of MUIC for school-age children, both pregnant women and school-age children would have optimal iodine intakes in 20 of China’s 31 provinces, based on the results of the 2011 National IDD Survey (Table 4).…”

“…The National Food Safety Assessment Committee conducted a risk assessment in 2009 [80] and again in 2016 [81]. China participated in a multi-country study to evaluate whether salt iodization can achieve optimal iodine status in all population groups [82] and undertook studies on the safe upper level of iodine intake in adults [83] and optimal urinary iodine ranges in school children [52]. Overall, the data indicate that while the MUIC of school-age children is in the “above adequate” range in several provinces, there is no consistent evidence of negative impacts on thyroid function or increases in thyroid disease that can be attributed to excess iodine intake from salt.…”

Чи Існує Зв’язок Між Хворобою Хашимото І Рівнем Йоду В Сечі?

“…Similar studies investigating the relationship between thyroid volume and UIC in literature have shown the role of iodine deficiency or excess iodine intake in the increase of goiter and thyroid volume. Significant increase in thyroid volume and goiter prevalence were found in patients with UIC > 300 μg/L [23,24].…”