Dietary and Urinary Iodine in Relation to Thyroid Cancer Risk: A Meta-Analysis

IntroductionThe influence of iodine on papillary thyroid carcinoma (PTC) remains a subject of debate. This meta-analysis was conducted to evaluate the risk association between varying levels of iodine intake and the occurrence of PTC and different subtypes of thyroid carcinoma (TC), particularly papillary thyroid microcarcinoma (PTMC).MethodsFour databases-the Cochrane Library, Embase, PubMed, and Web of Science-were systematically searched for relevant studies published up until May 30, 2024. An updated search was conducted on November 20, 2025. Literature screening and information collection were performed according to predefined eligibility criteria. The Newcastle-Ottawa Scale (NOS) was used to appraise the quality of the eligible literature. Statistical analysis was performed using Stata 17.ResultsThis meta-analysis encompassed 17 studies involving 273 651 individuals. The findings revealed a correlation between high urinary iodine concentrations and an increased risk of TC (odds ratio [OR]: 6.43, 95% confidence interval [CI]: 2.72-15.22, <i>P</i> < .05). The elevated risk was observed for both PTC (OR: 7.56, 95% CI: 1.6-35.78, <i>P</i> < .001) and PTMC (OR: 8.96, 95% CI: 5.89-13.64, <i>P</i> < .001). These results suggested that greater urinary iodine concentrations were associated with a higher risk of TC. However, there was no significant association between dietary iodine intake and TC risk (OR: 0.75, 95% CI: 0.37-1.52, <i>P</i> > .05).ConclusionThis meta-analysis demonstrated a definitive link between high urinary iodine excretion and an increased risk of TC. The relationship between dietary iodine intake and TC requires further investigation. Considering the current limitations, future large-scale, multicenter, prospective investigations are anticipated to provide further validation.