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

Area of Science:

• Environmental Health
• Endocrinology
• Toxicology

Background:

• The impact of mercury (Hg) exposure on thyroid hormones (THs) in the general population remains unclear.
• Previous research has yielded inconclusive results regarding the association between mercury and thyroid function.

Purpose of the Study:

• To conduct a meta-analysis to determine the association between mercury exposure and thyroid hormone levels in the general population.
• To synthesize existing evidence on mercury's effects on thyroid stimulating hormone (TSH), triiodothyronine (T3), thyroxine (T4), free triiodothyronine (FT3), and free thyroxine (FT4).

Main Methods:

• A systematic search of PubMed, Web of Science, Embase, and Cochrane Library was performed for studies published up to July 20, 2020.
• Included were prospective and cross-sectional studies examining mercury exposure (in blood and urine) and THs levels.
• A random-effects model meta-analysis was employed to assess the association, with risk assessments conducted for study reliability.

Main Results:

• The meta-analysis included 13 studies, revealing a significant association between blood mercury levels and THs.
• Blood mercury was associated with increased TSH (β=0.55) and FT4 (β=0.47) levels, but a decrease in T4 (β=-0.02).
• Subgroup analyses showed positive correlations between blood mercury and TSH in children/adolescents and FT4 in pregnant women.

Conclusions:

• Mercury exposure in blood is significantly correlated with altered levels of TSH, T4, and FT4 in the general population.
• Findings underscore the importance of controlling mercury usage and enhancing thyroid protection measures.
• Further research may be warranted to elucidate specific mechanisms and population-specific risks.