Low blood lead concentrations and thyroid function of American adults.

Lead is often present in our environment, but its effect on thyroid function is still unclear. In this study, multiple linear regressions were performed between log-transformed blood lead levels and thyroid function parameters of 4652 adults from the 2007-2008 National Health and Nutrition Examination Survey. The models were adjusted for age, gender, race/ethnicity, smoking, alcohol consumption, body mass index, physical activity, iodine intake, medications, and bone mineral density. Blood lead concentrations (mean: 1.52 ± 1.20 μg/dL [range 0.18-33.12]) were inversely associated with total thyroxine (regression coefficients [β]: -0.22 [95% CI: -0.34, -0.09] in the general population, but were not correlated with thyroid stimulating hormone, total or free triiodothyronine, nor free thyroxine. Blood lead may have no effect on the thyroid function; however, it could be associated with decreased concentrations in thyroid-binding proteins.