Relationship between Blood Trihalomethane Concentrations and Serum Thyroid Function Measures in U.S. Adults

Area of Science:

• Environmental Health
• Endocrinology
• Toxicology

Background:

• Disinfection byproducts (DBPs), specifically trihalomethanes (THMs), are common environmental contaminants.
• Toxicological data suggest THMs can negatively impact thyroid function.
• Limited epidemiological evidence exists on the association between THM exposure and thyroid function in human populations.

Purpose of the Study:

• To investigate the association between blood concentrations of specific trihalomethanes (THMs) and serum thyroid function biomarkers in U.S. adults.
• To examine the relationship between THM exposure and thyroid autoimmunity markers.

Main Methods:

• Analysis of data from 2233 adults (≥20 years) from the 2007-2008 National Health and Nutrition Examination Survey (NHANES).
• Measurement of blood THM concentrations (chloroform, bromodichloromethane, dibromochloromethane, bromoform) and serum thyroid biomarkers (TSH, FT4, TT4, FT3, TT3, TPOAb, TgAb).
• Application of multivariable linear regression models to assess associations.

Main Results:

• Positive associations were observed between blood concentrations of chloroform (TCM), bromodichloromethane (BDCM), and total THMs with serum free thyroxine (FT4).
• Inverse associations were found between dibromochloromethane (DBCM) and total brominated THMs (Br-THM) with serum total triiodothyronine (TT3).
• THM exposure was not associated with serum levels of thyroid autoantibodies (TgAb or TPOAb), indicating no link to thyroid autoimmunity.

Conclusions:

• Exposure to trihalomethanes (THMs) is associated with altered thyroid function biomarkers, including changes in thyroxine and triiodothyronine levels, in U.S. adults.
• The study did not find evidence that THM exposure is associated with thyroid autoimmunity.
• These findings highlight a potential environmental impact of common disinfection byproducts on thyroid hormone regulation.