Background

Metabolic syndrome (MetS), a cluster of interconnected factors that directly increase the risk of cardiovascular disease (CVD) and type 2 diabetes mellitus (T2DM) [1], has drawn public attention for decades. In recent years, the prevalence of MetS in children and adolescents has gradually increased and has became a worldwide public health issue. In 2020, 2.8% children and 4.8% adolescents had MetS globally, equating to approximately 25.8 million children and 35.5 million adolescents [2]. According to Noubiap et al., among the 44 countries in their study, Nicaragua (5.2%), Iran (8.8%), and Mexico (12.3%) had the highest prevalence of MetS in children, and Iran (9.0%), United Arab Emirates (9.8%), and Spain (9.9%) had the highest prevalence of MetS in adolescents [2].

Sedentary behavior refers to any waking behavior such as sitting or learning with an energy expenditure of 1.5 metabolic equivalent task or less [3]. A sedentary lifestyle increases all-cause mortality and the risks for CVD, diabetes mellitus (MD), hypertension (HTN), and cancers [4, 5]. Nowadays, sedentary time remains high among children and adolescents, and in many countries, the trend keeps rising over the past few decades. Across the 97 countries with knowledge on sitting in the Global School-based Student Health Survey (GSHS), 25% boys and 24% girls aged 13–15 years reported sitting for more than 3 h/day in addition to sitting at school and for homework [6]. From 2007 to 2016, sitting time of U.S. adolescents increased from 7 h per day to 8.2 h per day [7].

A growing body of literature suggests that excessive use of electronic devices could lead to poor eye health [8, 9], risks of chronic disease such as obesity [10, 11], hypertension [12, 13], and insulin resistance [14], poor sleep [9], depression and anxiety [15, 16]. 95% U.S. adolescents reported having or accessing to a smartphone [17]. Prevalence of 11-15-year-olds watching TV for ≥2 h on weekdays ranged from 45% (Switzerland) to 69% (United Kingdom, Wales) among boys, and from 40% (Switzerland) to 72% (Bulgaria) among girls. Prevalence of playing computer games for ≥2 h on weekdays ranged from 32% (Switzerland) to 68% (Denmark) in boys, and from 11% (Finland) to 47% (Netherlands) in girls [6].

Studies have revealed that sedentary behavior and high screen time are associated with an increased likelihood of MetS [18,19,20], while modification of lifestyle-associated risk factors is critical for the prevention and management of MetS [21]. Meanwhile, childhood and adolescence are critical periods for establishing healthy living habits [22]. Therefore, it is necessary to assess and manage risk factors of MetS to improve their lives. We used the data from the China National Nutrition and Health Surveillance of Children and Lactating Mothers in 2016–2017 to investigate the relationship between sedentary behavior, screen time and MetS among Chinese children and adolescents aged 7–17 years.

Methods

Study design and participants

Data was obtained from the China National Nutrition and Health Surveillance of Children and Lactating Mothers in 2016–2017 [42]. A Korean study also found that adolescents aged 12–18 years with daily screen time ≥ 5 h had 3 times increased risk of abdominal obesity compared to those with daily screen time < 3 h [43]. One possible reasons is that adolescents with high screen time consumed less unprocessed foods and more ultra-processed foods [42]. Dietary patterns characterized by high consumption of sodium, animal fat, and refined carbohydrates, and low consumption of fiber are related to risks of elevated blood pressure and increased body adiposity in adolescents [44]. In addition to abdominal obesity, the study showed that screen time is a risk factor for MetS as well. According to Khan et al., students with screen time ≥ 2 h/day were 2.2 times more likely to have MetS [19]. A NHANES study also found a dose-dependent manner between screen time and MetS [45]. A Guangzhou study including 4523 children and adolescents aged 6–13 years suggested that compared to low-level screen time group, medium and high-level screen time groups had an increased likelihood of MetS [31].

Inconsistent with the previous study which found no association between abdominal obesity and sedentary behavior among inactive males and females [46], our study found both screen time and sedentary behavior were associated with abdominal obesity. Abdominal obesity, an establish risk factor and the most prevalent manifestation of MetS, is a maker of dysfunctional adipose tissue. A cohort study revealed that both screen-based and non-screen based sedentary behavior had associations with abdominal adipose tissue deposition [47]. And a robust inverse association was observed for physical activity and visceral adipose tissue accumulation [47]. Although our study controlled physical activity variables, it is recommended to be physically active to prevent abdominal obesity and MetS.

The strengths of this study include a large sample size that incorporated children and adolescents in 31 provinces that could represent the whole nation data, standardized questionnaires, anthropometric measurements, and clinical examinations. Nevertheless, several limitations warrant attention. First, it was a cross-sectional study which could not clarify the causal relationship between sedentary behavior, screen time and MetS. In addition, although completed face-to-face by trained investigators, all questionnaires were self-reported, which was easily subject to recall bias. Moreover, a subjective measure of self-reporting as a means of measuring the sedentary time and the screen time was not precise. Accelerometers and inclinometers that capture data directly from electronic devices are more objective and reliable [48]. However, several shortcomings including lack of a standard cutoff point, difficulty of examining patterns of sedentary time, and poor compliance with wearing the device limit the widespread use of them [48]. Maybe the future study that could combine subjective with objective methods could solve the problem. Besides, our study included both screen-based and non-screen-based sedentary behavior into sedentary behavior. Maybe we will separate them to examine the relationship between each of them and MetS in the future study.

Conclusions

In summary, this study shows that high levels of sedentary time and screen time were associated with an increased likelihood of MetS among Chinese children and adolescents. Thus, in order to avoid MetS, students, parents and schools should work together to develop a healthy lifestyle to reduce sedentary behavior and screen time.