Toenail mercury levels positively correlate with obesity and abdominal obesity among Korean adults

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Abstract

Background

Although previous studies have shown that short-term exposure to mercury is associated with obesity, it should be noted that mercury is not easily released and that it constantly accumulates in the body. However, few studies have explored the association between chronic mercury exposure and obesity. This study aimed to examine the association between chronic mercury exposure and obesity in Korean adults.

Methods

The study used baseline data from the Trace Element Study of Korean Adults in Yeungnam area. A total of 495 participants aged 40–69 years who provided the required information (demographic, diet, lifestyle, toenail mercury levels, and health examination results) were included. Toenail mercury levels were measured using neutron-activation analysis. Body mass index and waist circumference were obtained from medical examination. Multivariable-adjusted logistic regression and restricted cubic spline regression were used in the analysis.

Results

In the fully adjusted logistic regression models, participants with the highest toenail mercury levels had a higher prevalence of obesity (odds ratio [OR]: 3.26, 95 % confidence interval [CI]: 1.79–5.93) and abdominal obesity (OR: 2.30, 95 % CI: 1.15–4.59). In the cubic spline regression model, linear relationships were confirmed between increased toenail mercury levels and higher prevalence of obesity and abdominal obesity (all p > 0.05 for nonlinearity).

Conclusions

In summary, chronic mercury exposure was associated with higher prevalence of obesity and abdominal obesity in Korean adults. Therefore, the development of public health interventions against environmental exposure of foods is required to manage and prevent obesity.

Introduction

Obesity is a significant human health risk that is rapidly increasing worldwide [1]. According to the World Health Organization (WHO) report, approximately two billion people are overweight worldwide, and a third of these are people with obesity [2]. The Korea Centers for Disease Control and Prevention has reported that the prevalence of obesity in Korea was 34.1 % in 2017, and this has been rising since 2005 when it exceeded 30 % [3]. Obesity increases the risk of a number of health complications, including type 2 diabetes, cardiovascular disease, and cancer, and exacerbates socioeconomic burdens; therefore, strategies targeting obesity are required to achieve the public health goal of disease prevention [4].

Numerous studies have identified factors contributing to the development of obesity such as diet, lifestyle habits, and genetics [5,6]. Recently, there is increasing evidence suggesting that environmental pollutants affect the development of obesity [7,8]. Chronic exposure to environmental pollutants is known to interfere with the normal functioning of the endocrine system [9]. Of these, mercury is a particularly toxic and highly reactive liquid heavy metal [10]. Absorption by the body of even a small amount of mercury may adversely affect the endocrine signaling pathways [11]. In addition, the accumulation of mercury in the body interferes with carbohydrate [12] and lipid metabolism [13], which may lead to obesity.

A cross-sectional study conducted in Taiwan found that blood mercury levels were positively correlated with the waist circumference (WC) [14]. A study in Greenland revealed similar findings and reported a positive association between blood mercury levels and the waist-to-hip ratio but not body mass index (BMI) [15]. In contrast, the Modeling the Epidemiologic Transition Study conducted in Ghana, South Africa, Seychelles, Jamaica, and USA found no significant association between blood mercury levels and overweight, obesity, and abdominal obesity [16]. Several studies on the Korean population demonstrated a significant association between blood mercury levels and obesity and abdominal obesity [17,18]. A previous study using the Trace Element Study of Korean Adults in Yeungnam area (SELEN) cohort showed that age-adjusted BMI and WC were higher among those with high toenail mercury levels [23]. However, previous studies, including those from Korea, have analyzed mercury levels using blood samples, which may only reflect short-term exposure to mercury [2,[16], [17], [18], [19], [20], [21]]. Hair and fingernails are biomarkers of long-term exposure to mercury; however, their use is limited because of contamination by substances such as shampoo, hair dye, and nail polish [22]. In addition, in-depth analyses considering multiple potential confounding variables and focused discussion regarding the association between mercury exposure and obesity are limited.

Therefore, we primarily evaluated the association between chronic mercury exposure and obesity using toenail samples which reflect relatively long-term exposure to mercury and are less likely to have contaminants [22].

Section snippets

Study population

This study used the baseline data from the SELEN cohort study. The survey methods of the study have been reported in detail elsewhere [23]. Briefly, the SELEN cohort is an ongoing prospective cohort study, established to identify the level of trace minerals and investigate the association with the risk of chronic diseases among residents in Yeungnam area of Korea. Baseline data including general characteristics, lifestyle, health examination results, and toenail mercury levels were collected

Results

The general characteristics of the 495 participants of the SELEN study were compared based on the tertiles of toenail mercury levels (Table 1). The median levels of toenail mercury were 0.21, 0.34, and 0.56 μg/g in each group, respectively. Participants with high levels of toenail mercury tended to be men, older, drinkers, current smokers, and had higher levels of education, monthly household income, and triglycerides than those with low levels of toenail mercury. In addition, among food

Discussion

This study investigated the association between toenail mercury levels and the prevalence of obesity and abdominal obesity among Korean adults using baseline data of the SELEN cohort. The results indicated that toenail mercury levels were associated with the prevalence of obesity and abdominal obesity and this positive association was linear.

Environmental pollutants are chemical substances that have been accumulated in the earth due to rapid modernization and continuous industrialization [30].

Conclusions

In conclusion, this study provides evidence that chronic mercury exposure is associated with obesity and abdominal obesity. Therefore, environmental exposure such as mercury should be considered together with the nutrient composition of foods. In addition, the development of public health intervention against environmental exposure of foods is required for managing and preventing obesity.

Author contributions

Data curation, formal analysis, visualization, software, and writing the first draft of the manuscript were performed by JJ. JJ and KP contributed to the investigation. JSM performed the assays and reviewed the manuscript. Conceptualization, funding acquisition, project administration, supervision, writing review, and editing were performed by KP. All authors read and approved the final manuscript.

Funding

This work was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT & Future Planning (grant number: NRF-2017R1A1A3A04069759). The funding sponsor had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, and in the decision to publish the results.

Declaration of Competing Interest

The authors report no declarations of interest.

Acknowledgments

The authors thank Hyo-Jin Kim, Sle Koo, and Sukyung Cho for their technical contributions to the SELEN study. In addition, the authors thank the University of Missouri Research Reactor staff for performing neutron activation analysis of the samples.

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