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. 2013 Feb;121(2):181-6.
doi: 10.1289/ehp.1205239. Epub 2012 Nov 16.

Thyroid hormones in relation to lead, mercury, and cadmium exposure in the National Health and Nutrition Examination Survey, 2007-2008

Aimin Chen  1 , Stephani S Kim, Ethan Chung, Kim N Dietrich
Affiliations

Thyroid hormones in relation to lead, mercury, and cadmium exposure in the National Health and Nutrition Examination Survey, 2007-2008

Aimin Chen et al. Environ Health Perspect. 2013 Feb.

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.

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Conflict of interest statement

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

Figures

Figure 1
Figure 1
Estimated thyroid hormone levels according to natural log blood total Hg or urinary Cd exposure quintiles in adults, NHANES 2007–2008. (A) TT4 by blood total Hg quintiles, (B) TT3 by blood total Hg quintiles, (C) TT4 by urinary Cd quintiles, (D) TT3 by urinary Cd quintiles.
See this image and copyright information in PMC

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