Thyroid Hormones in Relation to Lead, Mercury, and Cadmium Exposure in the National Health and Nutrition Examination Survey, 2007–2008

Aimin Chen, Stephani S. Kim, Ethan Chung, and Kim N. Dietrich


Department of Environmental Health, Division of Epidemiology and Biostatistics, University of Cincinnati College of Medicine, Cincinnati, Ohio, USA


Abstract

Background: Heavy metals, such as lead (Pb), mercury (Hg), and cadmium (Cd), are known toxicants, but their associations with the thyroid axis have not been well quantified at U.S. background levels.


Objectives: We investigated the relationships between thyroid hormones (total and free thyroxine [TT₄ and FT₄], total and free triiodothyronine [TT₃ and FT₃], thyroid-stimulating hormone [TSH], and thyroglobulin [Tg]) and levels of Pb, Hg, and Cd in blood and Cd in urine.


Methods: We separately analyzed a sample of 1,109 adolescents (12–19 years of age) and a sample of 4,409 adults from the U.S. National Health and Nutrition Examination Survey (NHANES) 2007–2008. We estimated associations after adjusting for age, sex, race, urinary iodine, body mass index, and serum cotinine.


Results: The geometric mean (GM) levels of blood Pb (BPb), total Hg, and Cd were 0.81 µg/dL, 0.47 µg/L, and 0.21 µg/L in adolescents and 1.43 µg/dL, 0.96 µg/L, and 0.38 µg/L in adults, respectively. The GMs of urinary Cd were 0.07 and 0.25 µg/g creatinine in adolescents and adults, respectively. No consistent pattern of metal and thyroid hormone associations was observed in adolescents. In adults, blood Hg was inversely related to TT₄, TT₃, and FT₃ and urinary Cd was positively associated with TT₄, TT₃, FT₃, and Tg, but there were no associations with Pb. Associations were relatively weak at an individual level, with about 1–4% change in thyroid hormones per interquartile range increase in Hg or Cd.


Conclusions: Our analysis suggests an inverse association between Hg exposure and thyroid hormones, and a positive association between Cd exposure and thyroid hormones in adults.


Key words: cadmium, heavy metals, lead, mercury, thyroid hormones. 


Environ Health Perspect 121:181–186 (2013). http://dx.doi.org/10.1289/ehp.1205239 [Online 16 November 2012]


Address correspondence to A. Chen, Division of Epidemiology and Biostatistics, Department of Environmental Health, University of Cincinnati College of Medicine, 3223 Eden Ave., Cincinnati, OH 45267-0056 USA. Telephone: (513) 558-2129. E-mail: aimin.chen@uc.edu


Supplemental Material is available online (http://dx.doi.org/10.1289/ehp.1205239).


This work was supported in part by the Center for Environmental Genetics (grant P30ES006096) and by the National Institute of Environmental Health Sciences (grant RC4ES09755).


The authors declare they have no actual or potential competing financial interests.


Received 20 March 2012; Accepted 15 November 2012; Online 16 November 2012.