Small particles, big impact: A narrative review of microplastics and their effects on thyroid function

Microplastics (MPs, 1 µm–5 mm) and nanoplastics (NPs, < 1 µm) have infiltrated virtually every corner of our environment and human tissues, raising concerns about potential health impacts, particularly regarding thyroid function. This narrative review synthesizes current evidence linking MP exposure to thyroid dysfunction and examines the mechanisms, vulnerable populations, and public health implications. We conducted a comprehensive narrative review of the literature on MPs and thyroid function, using electronic databases including PubMed/MEDLINE, Web of Science, Scopus, and Google Scholar, and included 62 articles relevant to MP-thyroid interactions. Multiple pathways link MP exposure to thyroid disruption: plastic additives, such as phthalates and BPA directly interfering with hormone production and signaling; environmental contaminants hitchhiking on MP surfaces; and the physical particles themselves triggering inflammatory and oxidative stress responses in thyroid tissue. Of particular concern are vulnerable populations – pregnant women, developing fetuses, and children – where even subtle hormonal disruptions may have lifelong consequences. Recent detection of MPs in human placenta, blood, and thyroid tissue confirms internal exposure. While significant research gaps remain, particularly regarding long-term human exposure effects, mixture toxicity, and dose-response relationships at environmentally relevant concentrations, emerging evidence suggests MPs represent a significant threat to thyroid health. A precautionary approach to minimize exposure is warranted, particularly for vulnerable populations.