Association between mercury exposure and thyroid hormones levels: A meta-analysis

The relationship between mercury (Hg) exposure and thyroid hormones (THs) levels in the general population has been inconclusive. We conducted a random effects model meta-analysis to identify the association between Hg exposure and THs levels in the general population.

This meta-analysis were performed based on the PECO questions (P = general population; E =1ug/L Hg in blood and urine; C =1ug/L incremental increase on; and O = variation of THs levels). We searched four electronic databases including PubMed, Web of Science, Embase, and Cochrane Library for studies published on or before 20th July 2020. Prospective and cross-sectional studies that evaluated the association between Hg exposure and the levels of thyroid stimulating hormone (TSH), triiodothyronine (T3), thyroxine (T4), free triiodothyronine (FT3), and free thyroxine (FT4) were included. We also assessed aggregate risks for the reliability of the included studies.

Initially, we retrieved 4889 articles. 18 studies met our inclusion criteria after screening and 13 articles were eligible to be included in the meta-analysis. The meta-analysis results suggest that blood Hg may be significantly associated with THs levels. The presence of Hg in blood may significantly increase the levels of TSH (β=0.55; 95%CI: 0.20,0.90; p < 0.001) and FT4 (β=0.47; 95%CI: 0.11,0.82; p < 0.001), with the opposite association in T4 (β=-0.02; 95%CI: 0.02, -0.01; p < 0.001). For the subgroup analysis, blood Hg was positively correlated with TSH levels in children and adolescents (β=0.62; 95%CI: 0.09, 1.15; p < 0.001) and FT4 levels in pregnant women (β=1.00; 95%CI: 0.99, 1.00; p < 0.001) respectively.

This meta-analysis indicates that exposure to Hg in blood could significantly corrrelate with the levels of TSH, T4, and FT4 in the general population. Therefore, it is crucial to control the use of Hg and strengthen protection of the thyroid.