Iodine Intake from Universal Salt Iodization Programs and Hashimoto's Thyroiditis: A Systematic Review.

Area of Science:

• Endocrinology
• Public Health
• Nutrition Science

Background:

• Hashimoto's thyroiditis (HT) involves autoimmune thyroid destruction, often linked to micronutrient status, including iodine.
• Both iodine deficiency and excess can disrupt thyroid function and promote autoimmunity.
• Universal Salt Iodization (USI) programs aim to ensure adequate iodine intake but may influence HT prevalence.

Purpose of the Study:

• To systematically review and analyze the temporal changes in Hashimoto's thyroiditis prevalence following the implementation of USI programs.
• To investigate the association between iodine intake through salt and the occurrence of thyroid autoimmunity.

Main Methods:

• A systematic literature search was conducted across multiple databases (PubMed, Scopus, Web of Science, etc.) from January 1965 to January 2025.
• Search terms included "iodine", "salt", "intake", "prevalence", and "Hashimoto's thyroiditis".
• Included studies reported study design, population, sample size, country, post-USI evaluation period, and thyroid antibody positivity.

Main Results:

• Out of 74 identified studies, 31 specifically evaluated thyroid antibody levels after USI implementation.
• Data from these studies were scrutinized using the JBI Critical Appraisal Checklist.

Conclusions:

• Excessive iodine intake, potentially driven by USI programs lacking robust monitoring, may be a significant factor in Hashimoto's thyroiditis prevalence.
• Achieving a balance between recommended salt intake, effective USI strategies, and population thyroid health outcomes remains a key challenge.