U-Shaped Associations between Urinary Iodine Concentration and the Prevalence of Metabolic Disorders: A Cross-Sectional Study

Abstract

Background: Iodine is important in both thyroid function and human metabolism. Studies have explored the effect of iodine on metabolic disorders through thyroid function. This study aimed to investigate the relationship between iodine status and metabolic disorders.

Methods: Data were obtained from the TIDE program, including 51795 subjects aged ≥18 years. The prevalence of metabolic disorders and its related components were calculated based on the level of urinary iodine concentrations (UICs) using the chi-square method. To further explore whether prevalence was associated with UIC, quadratic and UIC-stratified logistic regression models were used.

Findings: The prevalence of metabolic disorders presented as a U-shaped curve as the UICs change with a lower prevalence of 76% at a UIC of 300-499 µg/L. After adjusting for confounding factors, UIC of 300-499 µg/L was found to be a protective factor for metabolic disorders [OR=0·857, 95%CI (0·796-0·922)] and hypertension. A UIC of 300-799 µg/L was found to be protective against the occurrence of metabolic syndrome (MetS), impaired fasting glucose (IFG). 500-799 µg/L was protective against the occurrence of prediabetes, UIC ≥ µg/L was found to be protective against the occurrence of dyslipidemia. Furthermore, a UIC of <100 µg/L was a risk factor for hypertension.

Interpretation: The association between UICs in adults and metabolic disorders and its components is U-shaped. The beneficial effect of UIC on metabolic disorders disappears in cases of iodine deficiency (<100 µg/L) or excess (>500 µg/L).

Funding Statement: This work is supported by the Research Fund for Public Welfare from National Health and Family Planning Commission of China (Grant No. 201402005).

Declaration of Interests: All authors declare no competing interests.

Ethical Approval Statement: The ethics committee approved the study protocol.