Long Tan

Exploration of the safe upper level of iodine intake in euthyroid Chinese adults: a randomized double-blind trial

BACKGROUND The beneficial health effects associated with Universal Salt Iodization are well known. Yet, little is known about the possible adverse health effects in people with high iodine intake and the safe daily intake upper limit in the Chinese population. OBJECTIVE The objective of this study was to explore the safe upper level of total daily iodine intake among adults in China. DESIGN A 4-wk, double-blind, placebo-controlled, randomized controlled trial was conducted in 256 euthyroid adults. Participants were randomly assigned to 12 intervention groups with various iodine supplement doses ranging from 0 to 2000 μg/d. Total iodine intake included iodine from both supplements and diet. Multiple outcome measures were used to evaluate possible adverse effects, including thyroid function, thyroid size, and urinary iodine. RESULTS The mean iodine intake from the diets and salt intake of the participants were 105 ± 25 and 258 ± 101 μg/d, respectively. In comparison with the placebo group, all iodide-supplemented groups responded with significant increases in median urinary iodine concentrations (P < 0.05) and in thyroid-stimulating hormone concentration (P < 0.05). Thyroid volume decreased after 4 wk in the high-iodine intervention groups (1500-2000 μg). Subclinical hypothyroidism appeared in the groups that received 400 μg I (5%) and 500-2000 μg I (15-47%). CONCLUSIONS This study showed that subclinical hypothyroidism appeared in the participants who took the 400-μg I supplement, which provided a total iodine intake of ∼800 μg/d. Thus, we caution against a total daily iodine intake that exceeds 800 μg/d in China and recommend further research to determine a safe daily upper limit.

Long-Term Exposure to Excessive Iodine from Water Is Associated with Thyroid Dysfunction in Children

Previous studies have indicated an association between iodine excess and increased incidence of thyroid dysfunction in adults. However, there have been few studies on how the intake of excessive iodine affects thyroid function in children. The objective of this study was to assess the effects of a long-term exposure to excessive iodine on thyroid dysfunction in children. Urinary iodine concentration (UIC) and thyroid function in 371 children from a high iodine (HI) area (water iodine: 150-963 μg/L) and 150 children from an adequate iodine (AI) area (water iodine: 12.8-50.9 μg/L) were measured. The water iodine concentration in the HI area was higher than that in the AI area (P < 0.001) and the median urinary iodine concentration of children in the HI area was 1030 μg/L, which was 8.6 times that of children in the AI area (123 μg/L) (P < 0.001). Children in the HI area had a higher concentration of sensitive thyroid stimulating hormone and higher positivity of both thyroid peroxidase antibody (TPOAb) and thyroglobulin antibody (TGAb). The prevalence of thyroid diseases was higher in HI area children than that in AI area children (P = 0.000), especially subclinical hypothyroidism (SCH; P = 0.004). A body mass index (BMI) of ≥ 22.3 kg/m(2) was associated with the incidence of SCH (OR: 5.51; 95% CI: 1.52, 19.9; P = 0.009). UIC ≥ 600 μg/L (OR: 3.62; 95% CI: 1.22, 10.8; P = 0.024) and TPOAb or TGAb-positivity (Ab+ OR: 6.48; 95% CI: 1.78, 23.6; P = 0.005) in children were significantly and independently associated with SCH. Interactions between UIC ≥ 800 μg/L and Ab+ (P-interaction = 0.004) were found. Furthermore, increased thyroid volume was correlated with higher UIC (β = 0.22; P = 0.002). Excessive iodine intake in children in HI areas is associated with impaired thyroid function; UIC ≥ 600 μg/L and Ab+ are the risk factors for SCH. Effective measures need to be taken for reducing excessive iodine intake.

Prevalence of thyroid dysfunction with adequate and excessive iodine intake in Hebei Province, People's Republic of China.

OBJECTIVE To explore (i) the prevalence of thyroid dysfunction in populations with adequate and excessive iodine intakes and (ii) the effect of iodine exposure on the prevalence of thyroid dysfunction. DESIGN Cross-sectional study was conducted in Hebei in 2010. The population was classified as having adequate or excessive iodine intake according to the iodine concentration in drinking water. Demographic information was collected by questionnaire. Levels of serum thyroid hormones, thyroid autoantibodies and iodine in drinking water and urine were measured. SETTING Villages with adequate or excessive drinking water iodine in Hebei Province, Peoples Republic of China. SUBJECTS A total of 854 men and women aged 20-50 years who had lived in the surveyed areas for over 5 years, including 348 from the adequate iodine area (AIA) and 506 from the excessive iodine area (EIA). RESULTS Median urinary iodine concentration was 185 μg/l in AIA and 1152 μg/l in EIA. The prevalence of thyroid dysfunction in AIA was 10.3%, which included 1.1% with hypothyroidism and 8.1% with subclinical hypothyroidism; and 20.6% in EIA, which included 3.6% with hypothyroidism and 13.6% with subclinical hypothyroidism. The positive rates of thyroglobulin antibody were 16.1% in AIA and 11.9% in EIA; the positive rates of thyroperoxidase antibody were 20.7% in AIA and 16.4% in EIA. CONCLUSIONS Excessive iodine intake may lead to increased prevalence of biochemical thyroid dysfunction, especially biochemical hypothyroidism. This is not related to an increase in prevalence of thyroid antibodies. Women are more susceptible to iodine excess.

Neonatal thyroid function born to mothers living with long-term excessive iodine intake from drinking water.

The effects of long‐term excessive maternal iodine intake on neonatal thyroid function are less known. This study aimed to assess the effects of maternal excessive iodine intake from drinking water on thyroid functions of both mothers and their neonates.

Selenium Supplementation Alleviates Autoimmune Thyroiditis by Regulating Expression of Th1/Th2 Cytokines

Selenium (Se) is an essential trace element.Autoimmune thyroid diseases (AITD) are destructive inflammatory or anti-receptor autoimmune diseases characterized by reactivity to self-thyroid antigens.However,the effects of Se on the cytokines in AITD are still unclear.So we researched the role of Selenium (Se) and Th1/Th2 cytokine productions in the pathogenesis of autoimmune thyroid diseases (AITD).The data shown that high Se intake reduced the autoantibody titers and alleviated the pathological

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

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 μg/L (69-406 μg/L). The median (IQR) 24-h urinary iodine concentrations for the 2 collections were 381 μg/L (203-649 μg/L) and 398 μg/L (202-687 μg/L), respectively. The median (IQR) habitual daily iodine intake of children was 298 μg/d (186-437 μg/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 ∼5% for children aged 7-10 and 11-14 y at iodine intakes of 200-249 and 250-299 μg/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 μg/d. CONCLUSIONS Tvol begins to increase in children when iodine intake is ≥150 μg/d, and the TGR exceeds 5% when daily iodine intake is ≥250 μg/d for children aged 7-10 y and ≥300 μg/d for children aged 11-14 y. Our findings suggest that 150-249 and 150-299 μg/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.

24-Hour Urine Samples Are More Reproducible Than Spot Urine Samples for Evaluation of Iodine Status in School-Age Children

BACKGROUND Variation in different urinary measurements for evaluation of iodine status is of concern to clinicians and researchers. OBJECTIVE This study evaluated variations between urine iodine concentration (UIC), spot and 24-h urine sample creatinine concentrations, and 24-h urine iodine excretion (24-h UIE) in repeated samples from school-age children. METHODS Urine samples (24 h and morning spot) were collected on 2 occasions from 981 children in Ningjin and Lingxian counties, China. Samples from Ningjin were collected in October and November 2013, and samples from Lingxian were collected in April and May 2014. Morning spot urine iodine concentration (MUIC), morning spot urine creatinine, 24-h UIC, and 24-h urine creatinine were measured in all samples. The 24-h UIE was calculated by multiplying the 24-h UIC by the 24-h urine volume. RESULTS In Ningjin County, the 24-h UIC and 24-h UIE did not differ between repeated collections [192 and 172 μg/L, respectively, for 24-h UIC (P = 0.08); 123 and 120 μg/L, respectively, for 24-h UIE (P = 0.56)], whereas the MUIC was lower in November 2013 than in October 2013 (170 and 190 μg/L, respectively; P = 0.034). In Lingxian County, no significant differences were observed in 24-h UIC between the repeated collections (230 and 218 μg/L, respectively; P = 0.79), whereas the 24-h UIE and MUIC were higher in the samples collected in May 2014 than in April 2014 [161 and 155 μg/L, respectively, for 24-h UIE (P = 0.002); 244 and 203 μg/L, respectively, for MUIC (P < 0.001)]. When data from both counties were combined, no difference was observed between repeated 24-h UIC (214 compared with 196 μg/L; P = 0.17) and 24-h UIE (143 compared with 143 μg/d; P = 0.06), but MUICs were lower in the first collection than in the second collection (199 and 207 μg/L, respectively; P = 0.002). The κ values were >0.4 for 24-h UIC and mean UIE, whereas relatively low κ values were observed for MUIC and mean UIE. CONCLUSION The 24-h UIC was more accurate and reproducible than the MUIC in evaluating iodine status in a large-scale population study of school-age children.

Reproducible and reliable general semiquantitative food frequency questionnaire for evaluating iodine intake in Chinese children

Iodine deficiency is a global issue that is correlated with a variety of diseases and can affect individuals of all ages. We hypothesized that a general, semiquantitative food frequency questionnaire (FFQ) could be a valuable tool to evaluate iodine intake in children. Study participants comprised 687 healthy children between the ages of 7 and 13 years. The FFQ was developed to assess habitual iodine intake over a 6-month period (FFQ1). A 3-day estimated food diary (3DEFD) and the habitual daily iodine intake, calculated from 2-repeated 24-hour urine iodine excretion, tested the intermethod relative validity of the FFQ. There were 92 children who also repeated the FFQ (FFQ2) 3 weeks later to assess for FFQ reproducibility. Iodine intake estimated by FFQ1 + water was significantly higher than that indicated by the 3DEFD + water (204 μg/d vs 156 μg/d, P < .001), whereas there were no differences between habitual daily iodine intake and FFQ1 + water (185 μg/d vs 204 μg/d, P = .223). The interclass correlation coefficients of iodine intake estimated by the FFQ1 and FFQ2 were 0.72 (P < .001). The FFQ1 + water was moderately correlated with the 3DEFD + water (Spearman correlation coefficient = 0.57, P < .001) as well as habitual daily iodine intake (SCC = 0.34, P < .001). The subjects classified into the same or adjacent quartiles ranged from 32% to 93%. The κ value α was 0.46 for FFQ1 and FFQ2 (P < .001) 0.27 for FFQ1 + water and 3DEFD + water (P < .001), and 0.09 for FFQ1 + water and habitual daily iodine intake (P < .001). The results showed this FFQ is a reliable and reproducible tool in evaluating iodine intake in Chinese children.

Severely low serum magnesium is associated with increased risks of positive anti-thyroglobulin antibody and hypothyroidism: A cross-sectional study

Trace elements, such as iodine and selenium, are closely related to autoimmune thyroiditis and thyroid function. Low serum magnesium is associated with several chronic diseases; however, its associations with autoimmune thyroiditis and thyroid function are unclear. We investigated the relationships between low serum magnesium, autoimmune thyroiditis, and thyroid function in 1,257 Chinese participants. Demographic data were collected via questionnaires, and levels of serum thyroid stimulating hormone, anti-thyroid peroxidase antibody, anti-thyroglobulin antibody (TGAb), free thyroxine, serum magnesium, serum iodine, and urinary iodine concentration were measured. Participants were divided into serum magnesium level quartiles (≤0.55, 0.551–0.85, 0.851–1.15, and >1.15 mmol/L). The median serum magnesium level was 0.89 (0.73–1.06) mmol/L; levels ≤0.55 mmol/L were considered severely low (5.9% of participants). The risks of TGAb positivity and Hashimoto thyroiditis (HT) diagnosed using ultrasonography in the lowest quartile group were higher than those in the adequate magnesium group (0.851–1.15 mmol/L) (p < 0.01, odds ratios [ORs] = 2.748–3.236). The risks of total and subclinical-only hypothyroidism in the lowest quartile group were higher than those in the adequate magnesium group (0.851–1.15 mmol/L) (p < 0.01, ORs = 4.482–4.971). Severely low serum magnesium levels are associated with an increased rate of TGAb positivity, HT, and hypothyroidism.

Anthropometry-based 24-h urinary creatinine excretion reference for Chinese children

To establish 24-h urinary creatinine excretion reference ranges based on anthropometry in healthy Chinese children, a cross-sectional survey was conducted using twice-sampled 24-h urine and anthropometric variables. Age- and sex-specific 24-h creatinine excretion reference ranges (crude and related to individual anthropometric variables) were derived. During October 2013 and May 2014, urine samples were collected. Anthropometric variables were measured in the first survey. Data of 710 children (377 boys and 333 girls) aged 8–13 years who completed the study were analyzed. No significant difference was observed in 24-h urine volumes between the two samples (median [interquartile range): 855.0 [600.0–1272.0) mL vs. 900.0 [660.0–1220.0) mL, P = 0.277). The mean 24-h urine creatinine excretion was regarded as representative of absolute daily creatinine excretion in children. Sex-specific, body-weight-adjusted creatinine excretion reference values were 15.3 mg/kg/day (0.1353 mmol/kg/day) for boys and 14.3 mg/kg/day (0.1264 mmol/kg/day) for girls. Differences were significant between boys and girls within the same age group but not across different age groups within the same sex. Ideal 24-h creatinine excretion values for height were derived for potential determination of the creatinine height index. These data can serve as reference ranges to calculate ratios of analyte to creatinine. The creatinine height index can be used to assess somatic protein status.