ASSOCIATION BETWEEN PERFLUORONONANOIC ACID (PFNA) AND THYROID HORMONE LEVELS IN THE U.S. POPULATION: A CROSS-SECTIONAL STUDY OF NHANES DATA, 2007-2008

PFNA is found in a wide array of consumer products, food, water, and air. Levels of PFNA in the environment continue to increase, and can accumulate over a lifetime. Thyroid hormones are responsible for regulating major processes of the human body. Decreasing levels of thyroid hormones could potentially interfere with essential metabolic processes. Results of this study help researchers better understand the levels of serum PFNA found in the U.S. general population, and adds to the growing body of knowledge of PFNA in relation to thyroid hormone levels. Purpose (a): Perfluorinated chemicals (PFCs) are widely used in many consumer products and have been linked with thyroid hormone disruption. Most studies have focused on perfluorooctonoic acid (PFOA) and perfluorooctane sulfonate (PFOS) exposures and thyroid hormone levels, but perfluoronananoic acid (PFNA) has shown to be associated with thyroid hormone levels in animal studies. More human studies are needed to assess PFNA in relation to thyroid hormone levels. We assessed the association between serum PFNA levels and serum thyroid hormone levels (T3, T4, and TSH) in the adult U.S general population. Methods (b): We analyzed data from the 2007-2008 National Health and Nutrition Examination Survey (NHANES) for participants 20 years of age and older. Sex-specific multivariable linear regression models were used to assess the association between perfluorononanoic acid (PFNA) and thyroid hormone measures of triiodothyronine (T3), thyroxine (T4), and thyroid stimulating hormone (TSH), separately, while adjusting for age, race, and BMI. Results (c): Higher concentrations of PFNA were found in males (males = 1.95 ng/mL and females = 1.60 ng/mL). There were statistically significant negative relationships with PFNA and T3 (p = 0.0013) and T4 (p = 0.0381) among males, after adjustment for age, race, and BMI, indicating that gender may be an effect modifier. Conclusions (d): PFNA is associated with decreasing T3 and T4 levels in males. However, there have been no consistent findings of an association between PFNA levels and thyroid hormone levels in previous studies. More evidence and research is needed to determine specific implications of PFNA exposure and thyroid function.