Zinc Status and Occurrence of Thyroid Cancer: Systematic Review and Meta-Analysis

Background and Objective: Thyroid cancer (TC) represents the most common group of endocrine tumors, and its incidence has increased over the last four decades. The imbalance of trace elements, such as zinc (Zn), has been investigated due to the thyroid's sensitivity to these elements. Zn is essential for thyroid hormone action and may be involved in the pathogenesis of TC. This systematic review and meta-analysis aim to contribute to the discussion on the association between low serum Zn concentrations and the occurrence of TC. Materials and Methods: The search was carried out in the PubMed/MEDLINE, Scopus, Embase, LILACS and Web of Science databases, including observational studies published until December 2024. The primary outcome was low serum Zn concentration and the occurrence of TC. Three independent reviewers selected the studies and extracted the data from the original publications. The risk of bias was assessed using the Newcastle-Ottawa Quality Assessment Scale. Data analysis was performed using R software (V.4.3.1), and heterogeneity was calculated using the I² statistic, with results based on random effects models. Results: A total of 10 studies (n = 7 case-control and n = 3 cross-sectional) with sample sizes ranging from 44 to 294 individuals were included. The results indicated that serum Zn levels were not significantly lower in patients with TC compared with healthy controls (mean difference: -251.77; 95% confidence interval: -699.09, 195.54; I² = 100%, very low certainty). Conclusions: Further investigations, including rigorously designed observational studies with representative samples and improved control of potential confounding variables are indispensable.