Abstract
Imbalances in thyroid-stimulating hormone (TSH) levels are associated with metabolic syndrome (MetS), and the underlying mechanism is partly in alignment with that of lead exposure causing MetS. Many studies have reported the association between lead exposure and MetS, but no study has considered the possibility of TSH mediating lead's effect on MetS. Therefore, we aimed to examine the association between lead exposure and MetS considering TSH as a partial mediator. The data of 1,688 adults (age ≥19 years) from the Korea National Health and Nutrition Examination Survey in 2013 were analyzed. The prevalence of MetS in the Korean population was 21.9%, and the geometric mean of blood lead and serum TSH levels were 1.96 μg/dL and 2.17 μIU/mL, respectively. The associations between blood lead levels, serum TSH levels, and MetS were determined through a multiple logistic regression analysis. Blood lead levels were positively associated with high TSH levels (upper 25%) with an odds ratio (OR) and 95% confidence interval (CI) of 1.79 (1.24, 2.58) per doubled lead levels. The increase in blood lead and serum TSH levels both positively increased the odds of developing MetS. The OR of MetS per doubling of blood lead level was 1.53 (1.00, 2.35), and was not attenuated after adjusting for TSH levels. These findings suggest that higher levels of blood lead are positively associated with serum TSH levels and MetS. By exploring the role of TSH as a partial mediator between lead and MetS, we verified that lead exposure has an independent relationship with MetS, regardless of TSH levels.
Highlights
Thyroid hormones play a key role in maintaining most of the basic metabolic processes in our body
We considered the possibility of a mediation effect by thyroid-stimulating hormone (TSH) and suggested that previous studies that reported the association between lead exposure and metabolic syndrome (MetS) could have been overestimating the effect of lead if TSH does have a mediation effect
A significant association between blood lead levels and MetS was observed in the general Korean population
Summary
Thyroid hormones play a key role in maintaining most of the basic metabolic processes in our body. They are significantly involved in the functions of the nervous, reproductive, and cardiovascular systems in both children and adults [1]. A significant link has been established between TSH and metabolic syndrome (MetS), which is a cluster of abdominal obesity, hypertriglyceridemia, low high-density lipoprotein cholesterol (HDL-C) levels, high blood pressure, and fasting glucose disorder [3,4,5]. The normal biosynthesis of cholesterol is disturbed by thyroid disorders, leading to changes in serum lipid concentration [6]. Atherogenic lipid alterations following thyroid dysfunction can affect the vasculature leading to elevated blood pressure [7]
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