The Association between Cadmium Exposure and Thyroid Function in Animals: A Systematic Review

Area of Science:

• Environmental toxicology
• Endocrinology
• Comparative physiology

Background:

• Cadmium (Cd) exposure is suspected to induce thyroid dysfunction.
• Existing research presents conflicting results regarding Cd's impact on the thyroid gland.
• Animal models are crucial for investigating Cd's effects on thyroid function.

Purpose of the Study:

• To systematically review and determine the association between cadmium exposure and thyroid function markers in animals.
• To synthesize findings on how Cd affects thyroid hormones and thyroid-stimulating hormone (TSH).

Main Methods:

• Comprehensive literature search conducted on Scopus, PubMed, Web of Science, and Google Scholar until May 2023.
• Inclusion of studies focusing on the relationship between Cd exposure and thyroid function in rodents and fish.
• Systematic analysis of 24 selected articles out of 171 initial search results.

Main Results:

• Cadmium exposure was associated with varied effects on thyroid function markers, including triiodothyronine (T3), thyroxine (T4), and thyroid-stimulating hormone (TSH).
• Observed effects included increases, decreases, or no significant changes in T3, T4, and TSH levels in exposed rodents and fish.
• The study highlights the complex and sometimes contradictory impact of Cd on animal thyroid physiology.

Conclusions:

• A clear association exists between cadmium exposure and thyroid dysfunction in animal models (rodents, fish).
• The relationship between Cd levels (blood, urine) and thyroid function in humans remains uncertain due to limited evidence and conflicting data.
• Further large-scale human cohort studies are recommended to elucidate the effects of Cd on human thyroid function.