ORIGINAL ABSTRACT

Background/Objectives: Thyroid dysfunction (hypo- and hyperthyroidism) and cancer incidence have increased over the past decades, possibly linked to environmental contributions from endocrine disrupting chemicals (EDCs). Glyphosate is one of the most widely used herbicides globally and has endocrine-disruptive properties. Because of the sensitivity of the thyroid gland to endocrine disruption and the increased glyphosate exposure worldwide, this comprehensive review aimed to summarize studies investigating the link between glyphosate/glyphosate-based herbicides (GBHs) and thyroid dysfunction in human, animal, and in vitro studies. Methods: PubMed, Scopus, and Embase were used to search for original studies assessing glyphosate or GBH exposure and thyroid-related outcomes through December 2024. Data were extracted on study design, population or model, exposure, and thyroid outcomes. A total of 28 studies, including 9 human, 3 in vitro, and 16 animal studies were included. Results: Human studies showed mixed findings with some suggesting associations between glyphosate exposure and altered thyroid hormone levels, while others found no significant effects. Animal studies, particularly in rodents and amphibians, showed thyroid hormone disruption and altered gene expression, especially after perinatal or developmental exposure. In vitro studies reported changes in thyroid-related gene transcription and cell viability, however at concentrations exceeding those seen in humans. Conclusions: While there is some evidence that glyphosate may disrupt thyroid function, differences in study populations, exposure assessment methods, species models, and exposure doses complicated the comparison and summarization of the results. Further mechanistic and longitudinal studies are needed to clarify the thyroid-specific risks of glyphosate exposure.