Association between thyroid function and urinary levels of 3,5,6-trichloro-2-pyridinol: data from NHANES 2007-2008

Data from National Health and Nutrition Examination Survey for the years 2007-2008 were used to evaluate the association between serum levels of thyroid-stimulating hormone (TSH), free triiodothyronine (FT3), free thyroxine (FT4), total triiodothyronine (TT3), total thyroxine (TT4), and thyroglobulin (TGN) with the urinary levels of 3,5,6-trichloro-2-pyridinol (TCPY). Gender-stratified regression models with log10-transformed values of thyroid hormones as dependent variables and TCPY tertiles, age, race/ethnicity, smoking and iodine sufficiency statuses, fasting time, body mass index, and poverty income ratio as independent variables were fitted. TCPY levels were not found to be associated with the levels of TSH, FT3, FT4, and TT3 for either males or females. TCPY levels in the third tertile as compared to first tertile were found to be negatively associated (p ≤ 0.01) with TT4 levels for both males and females. TGN levels for those males who were in third tertile of TCPY were statistically significantly lower (p < 0.01) than for those who had their TCPY levels in first or second tertile. Irrespective of age, gender, race/ethnicity, and smoking status, unadjusted TCPY levels for the period 2009-2010 were statistically significantly lower (p < 0.01) than TCPY levels during the period 2001-2002. TCPY levels for 2009-2010 were as low as 35.8% of what they were in 2001-2002 for adolescents and not more than 56.9% of what they were for 2001-2002 for males.