Link between Exposure to Pesticides and Thyroid Cancer Identified

The risk of thyroid cancer increased proportionately to the total number of pesticides subjects were exposed to 20 years before diagnosis or interview.

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Thyroid cancer. 3D illustration showing thyroid gland with tumor inside human body and closeup view of thyroid cancer cells/Dr_Microbe.

A recent research study conducted by the University of California has provided the first evidence supporting the hypothesis that residential pesticide exposure from agricultural applications is associated with an increased risk of thyroid cancer.

In single pollutant models and within a 20-year exposure period, 10 out of 29 selected pesticides were associated with thyroid cancer, including several of the most applied pesticides in the United States such as paraquat dichloride.

The risk of thyroid cancer increased proportionately to the total number of pesticides subjects were exposed to 20 years before diagnosis or interview.

The study which was published in The Journal of Clinical Endocrinology & Metabolism on 26th July 2022 had a sample size of 2067 cases and 1003 controls. Study participants were included if they were diagnosed with thyroid cancer, lived in the study area at their time of diagnosis, and were ≥35 years of age.

On the other hand, controls were recruited from the same area and eligible to participate if they were ≥35 years of age and had been living in California for at least 5 years prior to the interview.

The researchers performed a case-control study utilizing thyroid cancer cases from the California Cancer Registry (1999-2012) and controls sampled in a population-based manner. They examined residential exposure to 29 agricultural use pesticides, known to cause DNA damage in vitro or are known endocrine disruptors.

A validated geographic information system–based system to generate exposure estimates for each participant.

Thyroid cancer incidence has increased substantially in the U.S. during the past 30 years, rising by 3% annually, a trend some experts have attributed to better detection systems while other reports suggest environmental, genetic and lifestyle risk factors.

“The incidence of thyroid cancer has been increasing exponentially over the course of the last few decades,” said Dr. Avital Harari, corresponding author and principal investigator for the study.

“Additionally, the risk of advanced thyroid cancers, which can increase the risk of mortality and cancer recurrence, has been found to be higher in the state of California as compared to other states. Therefore, it is essential to elucidate risk factors for getting thyroid cancer and understand potentially alterable causes of this disease in order to decrease risks for future generations,” Harari added.

“Our research suggests several novel associations between pesticide exposure and increased risk of thyroid cancer,” she added. “Specifically, exposure to the pesticide paraquat is positively associated with thyroid cancer risk.”

Harari, an Associate Professor of Endocrine Surgery at UCLA Health, said additional research is needed. “Our study warrants further investigation to confirm these findings and better evaluate the actual mechanisms of action.”

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