Researchers examine link between pesticides and thyroid cancer risk in Central California area

In single pollutant models and within a 20-year period, 10 out of 29 reviewed pesticides were associated with thyroid cancer, including several of the most widely used ones in the U.S. These included paraquat dichloride, glyphosate and oxyfluorfen.

Additionally, the risk of thyroid cancer increased proportionally to the total number of pesticides subjects were exposed to 20 years before diagnosis or the research interview. In all models, paraquat dichloride was associated with thyroid cancer.

The study appears in The Journal of Clinical Endocrinology & Metabolism.

The authors say this study provides the first evidence supporting the hypothesis that residential pesticide exposure from agricultural use is associated with an increased risk of thyroid cancer.

Thyroid cancer incidence has increased substantially in the U.S. during the past 30 years, rising by 3% annually. Some experts attribute the increase to better detection methods, but other reports suggest environmental, genetic and lifestyle risk factors may also explain the upward trend. Few studies have examined environmental exposures on thyroid cancer occurrence, except those focusing on radiation exposure. Previous studies found higher risks for those working in the leather, wood and paper industries, as well as those exposed to environmental solvents, flame retardants and pesticides.

Certain pesticides are established mutagens or have been shown to induce tumor growth and chromosomal abnormalities in vitro. These include glyphosate — the active ingredient in widely used herbicides — and 19 pesticides that induce DNA cell damage in vitro. Pesticides also can alter thyroid hormone production, which has been associated with thyroid cancer risk.

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