2.1. Study Design

The KNHANES is a series of nationally representative population-based cross-sectional surveys concerning health and nutritional status that have been conducted using a stratified, multistage, and probability sampling design by the Korea Disease Control and Preventive Agency (KDCA) [21]. Our study used data from the questionnaire, physical examination components, laboratory indices, and diet assessment of the KNHANES V 1-3 and VI-1 (2010–2013). Among an initial enrolled sample of 15,261 men and 18,291 women, we excluded those who were aged younger than 10 years and older than 19 years, had no data on anthropometric measures, and had no measurement data on blood mercury levels (Figure 1). The final number of participants was 1327 (10–18 years of age; 672 male and 655 female), and the participants were divided into normal and overweight groups. Overweight was defined as a BMI ≥ 85th gender and age-specific percentiles based on the 2017 Korean growth chart [22]. The remaining participants comprised the normal group. The BMI was defined as the participants’ weight in kilograms divided by the height in meters squared (kg/m²). The WHtR was defined as the participant’s WC in cm divided by the height in cm. The participants were additionally divided into male and female groups.

Study Participants.