Trace Element Status and Hypothyroidism: A Systematic Review and Meta-analysis

The relationship between thyroid hormones metabolism and trace element levels has biological plausibility; however, previous reports that compared trace element levels in patients with hypothyroidism and healthy individuals yielded conflicting results. Therefore, the aim of this meta-analysis was to investigate the association between selected trace elements (i.e., selenium (Se), zinc (Zn), iron (Fe), manganese (Mn), copper (Cu), lead (Pb)), and magnesium (Mg) concentrations in patients with hypothyroidism and healthy controls. Electronic databases, including PubMed, Scopus, Embase, and Science Direct, were searched systematically until September 2019. Thirty-two observational studies were included in the final analyses. Hedges' g tests were used to estimate effect sizes, as trace element concentrations were reported using different measurement units across the studies. Selenium (Hedges' g = - 0.52; 95% CI = [- 1.05, - 0.002]; P = 0.049) and Zn (Hedges' g = - 0.86; 95% CI = [- 1.66, - 0.06]; P = 0.035) concentrations were significantly lower, whereas Pb concentrations were significantly higher (Hedges' g = 0.34; 95% CI = [0.10, 0.59]; P = 0.006) in patients with hypothyroidism compared with healthy controls. There were no differences in the concentrations of Fe, Cu, Mn, and Mg between the groups. Patients with hypothyroidism exhibited lower Se and Zn and increased Pb concentrations compared with healthy controls. High-quality studies with larger sample sizes are required to explicate the link between trace element status and hypothyroidism.