U-shaped relationship between iodine status and thyroid autoimmunity risk in adults

in European Journal of Endocrinology

Correspondence should be addressed to J Zhang; Email: zhangjinan@hotmail.com
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Background

Iodine status has long been regarded as an environmental determinant for thyroid dysfunction, but its relationship with thyroid autoimmunity (TAI) is still controversial. Our study aimed to elucidate the relationship between iodine status and TAI through both a population-based study and a dose–response meta-analysis of eligible epidemiological studies.

Methods

A population-based, cross-sectional study was firstly carried out, which enrolled a total of 2808 Chinese adults. Odds ratio (OR) with 95% confidence interval (95% CI) was calculated through logistic regression analysis. A dose–response meta-analysis of eligible epidemiological studies was also carried out.

Results

The cross-sectional study showed an U-shaped relationship between iodine intake and TAI in adults. Compared with those with more than adequate iodine status, individuals with iodine deficiency, adequate iodine status and iodine excess all had higher risk of TAI, and the adjusted ORs were 1.50 (95% CI 1.03–2.17, P = 0.032), 1.50 (95% CI 1.09–2.07, P = 0.013) and 1.68 (95% CI 1.11–2.53, P = 0.014), respectively. The dose–response meta-analysis included 22 epidemiological studies with a total of 69,987 participants and further validated the U-shaped relationship between iodine intake and TAI in adults, which proved the significantly increased risk of TAI among individuals with either iodine deficiency or iodine excess. Stratified analysis of studies with low risk of confounding bias also identified similar findings.

Conclusion

The study suggests an U-shaped relationship between iodine intake and TAI in adults, and both iodine deficiency and iodine excess are risk factors of TAI in adults. The underlying mechanisms need to be elucidated in future studies.

Supplementary Materials

    • Supplemental table 1 Clinical characteristics of study subjects in the cross-sectional study
    • Supplemental table 2 Risk of TPOAb positivity in adults with different urinary iodine concentration
    • Supplemental table 3 Risk of TGAb positivity in adults with different urinary iodine concentration
    • Supplemental table 4 Summary of the risk of bias and the quality of those included studies
    • Supplemental figure 1 Flow chart of study selection in the meta-analysis
    • Supplemental figure 2 Association between iodine intake and thyroid autoimmunity in adults in the dose-response meta-analysis of total 17 studies in adults when using adequate iodine status (UIC 100-199.9 μg/L) as reference (The reference level of UIC is 150 μg/L. The black solid line represents the odds ratio and the long black dash line represents 95% confidence intervals of the fitted nonlinear trend. The short dash line represents the linear trend. The spline model was the optimal model, while the curve for the linear model was shown to display the difference in the patterns between the spline model and the linear model.)
    • Supplemental figure 3 U-shaped association between iodine intake and thyroid autoimmunity in adults in the dose-response meta-analysis of 14 studies in adults with high risk of confounding bias (The reference level of UIC is 200 μg/L. The black solid line represents the odds ratio and the long black dash line represents 95% confidence intervals of the fitted nonlinear trend. The short dash line represents the linear trend. The spline model was the optimal model, while the curve for the linear model was shown to display the difference in the patterns between the spline model and the linear model.)
    • Supplemental figure 4 U-shaped association between iodine intake and thyroid autoimmunity in adults in the dose-response meta-analysis of 13 studies in adults with low risk of selection bias (The reference level of UIC is 250 μg/L. The black solid line represents the odds ratio and the long black dash line represents 95% confidence intervals of the fitted nonlinear trend. The short dash line represents the linear trend. The spline model was the optimal model, while the curve for the linear model was shown to display the difference in the patterns between the spline model and the linear model.)
    • Supplemental figure 5 U-shaped association between iodine intake and thyroid autoimmunity in adults in the dose-response meta-analysis of 14 studies in adults with good quality according to NOS criteria (The reference level of UIC is 250 μg/L. The black solid line represents the odds ratio and the long black dash line represents 95% confidence intervals of the fitted nonlinear trend. The short dash line represents the linear trend. The spline model was the optimal model, while the curve for the linear model was shown to display the difference in the patterns between the spline model and the linear model.)
    • Supplemental figure 6 Association between iodine intake and thyroid autoimmunity in children in the dose-response meta-analysis of 5 studies in children (The reference level of UIC is 50 μg/L. The black solid line represents the odds ratio and the long black dash line represents 95% confidence intervals of the fitted nonlinear trend. The short dash line represents the linear trend. The spline model was the optimal model, while the curve for the linear model was shown to display the difference in the patterns between the spline model and the linear model.)

 

     European Society of Endocrinology

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