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

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.

Associations between Thyroid Hormones and Blood and Urine Lead

“…For NHANES 2007-2012 data analyzed for this study, for general US population, unadjusted geometric mean blood lead levels were observed to be 1.36 ( [4] and Chen, et al [5], TSH levels were observed to increase with increase in the levels of blood lead for IOD and IOR males (p <= 0.04, Table 4) and for IOD females, blood lead levels had a negative association with the levels of TT3 (p = 0.01, Table 4). Even when the associations between blood levels and TSH, FT3, and TT3 were not observed to be statistically significant, irrespective of gender and IOS, there was always a positive association between TSH and blood lead and always a negative association between blood lead and FT3 and TT3.…”

“…Chen, et al [5] also used NHANES 2007-2008 data and did not find any associations of blood and urine lead with any of the thyroid hormones. Kahn, et al [6] reported lead exposure to contribute to maternal thyroid dysfunction by stimulating autoimmunity to the thyroid gland.…”

Alterations of Thyroid Hormone Levels in Cadmium Exposure

“…Blood cadmium concentration was associated with increasing TSH and diminishing FT4 [24]. In an evaluation of the relationship between cadmium exposure and thyroid hormones in the National Health and Nutrition Examination Survey (NHANES) 2007-2008, urinary cadmium was found to be positively associated with total T3, total T4, free T3, and thyroglobulin (Tg) [3] (Table 3). In this study, we found a positive correlation between whole blood cadmium levels and serum thyroid hormones.…”

“…Cadmium toxicity is associated with elevated incidences of chronic kidney disease, hypertension, osteoporosis, and leukemia, as well as cancers of the lung, kidney, urinary bladder, pancreas, breast, and prostate [2]. Thyroid hormones (THs) play a critical role in the functions of nervous, reproductive, and cardiovascular systems in both children and adults [3]. Iodothyronine deiodinases constitute a group of selenoproteins which initiate or terminate thyroid hormone action.…”

Disruption of iron homeostasis and resultant health effects upon exposure to various environmental pollutants: A critical review

“…Moreover, Pb can exert adverse effects on hematological, renal and gastrointestinal systems (Chen et al, 2013). It has been suggested that Pb poisoning could cause anemia through: (a) reducing heme contents (Alexander et al, 1998;Lachant et al, 1984;Moore et al, 1987;Oskarsson and Fowler, 1985), (b) inhibiting the activity of erythrocyte pyrimidine 5′nucleotidase (Valentine et al, 1976), and (c) triggering phosphatidylserine externalization on red blood cells and erythrophagocytosis (Jang et al, 2011).…”