The Agency for Toxic Substances and Disease Registry (ATSDR, 2020) indicates that there is evidence that certain heavy metals such as Pb and Hg can affect the endocrine system as an endocrine disruptor, affecting the physiological value of hormones and causing an endocrine imbalance. In the present study, it was shown that the free TSH T3 hormones were outside the reference values, which is associated with what has been reported by various epidemiological studies that relate exposure to Pb and Hg with alteration of thyroid function, as well as alteration of cortisol and insulin levels (Javorac et al., 2023, Pacheco et al., 2024). Some of the work that has been published includes retrospective human studies that have correlated exposure to Pb, Hg and even Cd with alterations in thyroid hormone function, finding a positive correlation between blood and urine concentrations of these metals with all thyroid hormones, as well as thyroglobulin (Tg)  (Chen et al ., 2013)

To understand what has been expressed above, it is essential to know that the toxic action of heavy metals on living beings occurs through the blocking of biological activities, that is, enzymatic inactivation by the formation of bonds between the metal and sulfhydryl groups (-SH) and other functional groups of proteins and enzymes, causing irreversible damage in different organisms, displacing other metal ions or modifying the active conformation of biological molecules.

Vukelić et al. (2023), in their study, explored the influence of Pb on thyroid hormones and thyroid-related antibody levels in the rat model and revealed that low doses of Pb cause an increase in thyroid hormones (T4, FT4 and TSH) in rats after subacute exposure, while they had no impact on T3, FT3, anti-TPO and anti-Tg. Thus, they emphasize that the dose-dependent effects were the increase in T4 and FT4, where in addition, the in silico toxicogenomic data analysis showed that the main molecular pathways related to Pb-induced hyperthyroidism are connected to 14 genes. A study by Nie et al. (2017) which included 5628 Chinese adults, showed the relationship of heavy metal levels in blood and serum antibodies against thyroid proteins and thyroid dysfunction reflected by total T3, total T4 and TSH levels.

Endocrine disruption has become a major human health problem, but it is difficult to study outside the laboratory for several reasons, including the multiplicity of exposures, the difficulty in assessing each exposure, and the variety of possible outcomes among human populations. In this regard, Castiello et al. (2020), examined the association of urinary concentrations of arsenic (As), cadmium (Cd), mercury (Hg), nickel (Ni), lead (Pb), manganese (Mn) and chromium (Cr) with blood pressure (BP) and serum hormone levels in male adolescents in Spain, showing significant associations between Hg and increased testosterone and luteinizing hormone (LH) and decreased thyroid-stimulating hormone (TSH); between the combination of As and Hg and increased LH and insulin-like growth factor 1; between Cr and decreased TSH; and between Cd and increased adrenocorticotropic hormone, concluding that these findings suggest that combined exposure to toxic metals, especially As and Cd, may contribute to elevated BP in male adolescents and that exposure to Hg, As, Cd and Cr may affect their hormone levels. Finally, a pilot study conducted by Nascimento et al. (2018), investigated the possible association between exposure to these xenobiotics and thyroid dysfunction in children living in a rural community in southern Brazil, and found that elevated levels of these metals, along with higher levels of Pb and Hg, were associated with alterations in thyroid hormones.

 Conclusions

Statistically significant differences were found in the average concentrations of TSH, T3F, lead and mercury in the study group. These results allow establishing a possible association of the aforementioned metals with hyperthyroidism, leaving then for the medical evaluation the definitive diagnosis and to consider within its profile the analysis of heavy metals.