Association between Blood Mercury Level and Visceral Adiposity in Adults

Corresponding author: Seong-Su Moon http://orcid.org/0000-0001-8881-3927 Department of Internal Medicine, Dongguk University College of Medicine, 123 Dongdae-ro, Gyeongju 38066, Korea E-mail: [email protected] Recently, there has been increasing concern with regard to health problems due to exposure to environmental pollutants, such as substances found in our food and consumer or industrial products that interfere with our body’s hormone synthesis, secretion, activity, and metabolism [1,2]. Heavy metals are considered as an endocrine-disrupting chemical that can interfere with the normal endocrine system and metabolism of humans. Mercury, the most dangerous of all heavy metals [3], is widely dispersed in the environment including air, soil, dust, water, and the human food chain [4]. Mercury exists in three basic forms: elemental, inorganic, and organic [5-7]. Inorganic mercury is the toxic species found in human tissue after conversion from other forms. Organic forms of mercury from fish and elemental mercury from dental amalgams are the major environmental sources of exposure to mercury [8]. In addition, mercury was also found in cosmetic powders, plastic toys, sea mammals, and thimerosal vaccines. The Environmental Protection Agency in United States reported the safe daily mercury intake to be less than 0.1 μg/kg/day [9]. One dental amalgam filling is estimated to release about 3 to 17 μg of mercury vapor daily [9]. Several kinds of vaccine contain thimerosol as a preservative, which is suspected to be another major source of mercury [6,7,9]. The long-lived large predatory fish such as swordfish, king mackerel, and tuna, which are favorite fish dishes of Koreans, contain about 0.5 to 1 μg of methyl mercury per gram [6,7,9]. Therefore, members of the general population, not only humans in contaminated area, are exposed daily to potential environmental hazards of mercury. Mercury has no known physiologic role in human metabolism, but mercury induces mitochondrial dysfunction and oxidative stress [10,11]. It has been suggested to cause insulin resistance which is one of the underlying pathogenetic mechanism of metabolic syndrome, a constellation of cardiovascular risk factors, including central obesity, dysglycemia, dyslipidemia, and hypertension. Mercury reduces antioxidant defense by binding to sulfhydryl groups of proteins, resulting in inactivation of numerous enzymatic reactions and amino acids and depletion of N-acetyl cysteine, α lipoic acid, and glutathione, which provide about 10% to 50% of the plasma protein antioxidant capacity [12]. Since mercury has a long half-life and the human body has no mechanisms to actively excrete mercury [12], mercury accumulates in human body during lifetime. So far, several in vivo, in vitro, and epidemiologic studies have investigated the metabolic effects of mercury on the risk of obesity, diabetes, and cardiovascular disease. Prevalence of hypertension and cardiovascular diseases, such as myocardial infarction and coronary heart disease, were increased as a consequence of mercury toxicity [13]. Blood mercury concentration showed an association with waist-hip ratio in Korean men [12]. Body mass index (BMI) and waist circumference (WC), indirect measures of adiposity, has been used to estimate the association between blood mercury concentration and obesity, but the findings have been inconsistent. Park et al. [14] showed that the blood mercury concentration was significantly associated with visceral adipose tissue (VAT) as measured by dualenergy X-ray absorptiometry (DXA). Because DXA VAT is considered to be an accurate, direct measure of adiposity, the finding could be more evident than previous studies. Besides Editorial Obesity and Metabolic Syndrome