Iodine Concentration in Iodide Salt and Its Association with Thyroid Disorders: A Systematic Review

Abstract

Introduction: Iodine is a crucial micronutrient necessary for the synthesis of thyroid hormones, which are essential for normal growth, development, and metabolism. Iodide salt, introduced as a public health strategy in the early 20th century, has significantly reduced iodine deficiency worldwide. However, disparities in iodine intake remain, and both iodine deficiency and excess can lead to thyroid disorders. This systematic review aims to evaluate the association between iodine concentration in iodide salt and the prevalence of thyroid disorders. Methods: A comprehensive literature search was conducted using databases including PubMed, Scopus, Google Scholar, Embase, Policy Commons, and Web of Science. Studies included were human research articles that examined the relationship between iodine concentration in iodide salt and thyroid disorders. Inclusion criteria encompassed primary studies such as randomized controlled trials, cohort studies, case-control studies, and cross-sectional studies published in English. Data extraction involved capturing study characteristics, iodine concentration levels, and thyroid disorder outcomes. The PRISMA reporting system was utilized to ensure systematic review procedures. Findings: The review identified significant findings across 8 studies included in this review namely Kotwal et al. (2015), Zhao et al. (2014) Atmis et al. (2021), Refaat and Azzeh (2020) and Fan et al. (2023) found similar trends in that deficiency and excessive iodine corelated with increased rates of thyroid disorders such as hypothyroidism, hyperthyroidism, and autoimmune thyroiditis across different age groups, gender and health conditions such as pregnancy. Li et al. (2020) and Meng et al. (2024) further demonstrated that salt iodization effectively reduced iodine deficiency-related thyroid disorders without significantly increasing hyperthyroidism or autoimmune thyroiditis. On the other hand, Vučinić et al. (2018) noted reduced goiter prevalence but an increase in autoimmune thyroiditis following increased salt iodization in Croatia. Conclusion: The review underscores the dual risks associated with both iodine deficiency and excess in the context of thyroid disorders. While iodide salt has successfully mitigated iodine deficiency, excessive iodine intake has emerged as a significant concern, particularly in regions with high iodization levels. Regular monitoring and adjustment of iodine levels are crucial to prevent both deficiency and excess related thyroid dysfunction.