The association between particulate matter 2.5 and thyroid function and thyroid cancer: a meta-analysis.

[PURPOSE] Recent studies indicate a potential link between exposure to atmospheric particulate matter 2.5 (PM2.5) and thyroid function, though epidemiological conclusions remain inconsistent. This comprehensive systematic review and meta-analysis aims to clarify the connection between PM2.5 levels and the risks of thyroid function and thyroid cancer.

[METHODS] Using the medical subject headings "PM2.5" and "thyroid hormones" along with their associated free words, publications from the Web of Science, Embase, Cochrane Library, and PubMed up to April 2024 were searched. The study protocol has been registered on PROSPERO (CRD42024554220).

[RESULTS] A total of 1322 articles were collected from databases, of which 27 studies were included in the analysis. The findings indicated that exposure to PM2.5 was a significant risk factor for hypothyroidism, increasing the incidence risk by 0.15 (95% CI 1.08, 1.23, P < 0.001). PM2.5 exposure levels were significantly higher in Asian populations than in European populations; each incremental increase in PM2.5 exposure resulted in a rise in TSH by 0.27 mIU/L (95% CI 0.07, 0.47, P = 0.008) and a decrease in FT4 by 0.21 pmol/L (95% CI - .35, - 0.07, P = 0.004). Additionally, in susceptible pregnant women, each incremental increase in PM2.5 exposure during pregnancy was associated with a rise in TSH levels by 0.08 mIU/L (95% CI - 0.02, 0.17, P < 0.001) and a decrease in FT4 levels by 0.09 pmol/L (95% CI - 0.23, 0.05, P = 0.210).

[CONCLUSION] Our research establishes PM2.5 exposure as a risk factor for diminished thyroid function. In Asian populations, the average level of PM2.5 exposure is high, significantly affecting thyroid hormones (TSH, FT4). Particular attention to PM2.5 exposure levels during pregnancy is essential to reduce the risk of thyroid dysfunction.