Ambient air pollution exposure and thyroid cancer incidence in Iran

Thyroid cancer is the most common endocrine malignant that is three times more prevalent in women than men. Fine particulate matter (PM2.5( has been indicated to affect Thyroid Hormone (TH) homeostasis. We sought to estimate the association between long-term exposure to ambient air pollution and the incidence of thyroid cancer in the Iranian female population.

We extracted thyroid cancer incidence and ambient air pollution data from Iran from 2000 to 2019 for males and females for all age groups from the Global Burden of Disease (GBD) dataset. We entered the data into Joinpoint to present Annual Percent Change (APC) and Average Annual Percent Change (AAPC) and its confidence intervals. We entered the information into R3.5.0.

Thyroid cancer in females had an upward trend [AAPC=4.9% (4.2-5.6)]. There was a correlation between ambient PM pollution (p≤0.001, r=0.84) and ambient ozone pollution (p≤0.001, r=0.94), and the incidence of thyroid cancer in females. The results of the analysis also showed a significant relationship between thyroid cancer incidence in females and secondhand smoke (p≤0.001, r=0.74).

This study indicated increasing trends in thyroid cancer incidence with exposure to ambient air pollution. Our novel findings provide additional insight into the potential associations between risk factors and thyroid cancer and warrant further investigation, specifically in areas with high levels of air pollution both nationally and internationally. However, causal relationships cannot be fully supported via ecological studies, and this article only focuses on Iran.