A study of primary school children shows that excess screen use is tied to higher body fat, while better cardiorespiratory fitness may help protect against some of its metabolic consequences.
Study: The association of screen time with childhood obesity and metabolic status: a mediation analysis of cardiorespiratory fitness. Image credit: Steve Heap/Shutterstock.com
A study published in Frontiers in Endocrinology reveals that higher screen time is associated with higher levels of body fat accumulation and less favorable obesity-related metabolic indicators in school-aged children, and that cardiorespiratory fitness can significantly influence this association.
Rising screen time coincides with growing childhood adiposity
Childhood obesity has become a major public health concern because of its exponentially increasing prevalence worldwide. During 2000–2023, the prevalence of obesity and overweight was estimated to be 8.5 % and 14.8 %, respectively, among children and adolescents.
Excessive fat accumulation is the main characteristic of obesity, which also contributes to various other chronic diseases, including cardiovascular disease, type 2 diabetes, and dyslipidemia.
Sedentary behavior, defined as sitting or lying down while awake, significantly contributes to unhealthy weight gain and unfavorable obesity-related metabolic patterns. Screen time, which refers to the time spent using electronic screen devices such as televisions, computers, tablets, and smartphones, is considered one of the most common sedentary behaviors.
International guidelines recommend restricting recreational screen time to a maximum of two hours per day for children and adolescents. However, a significant proportion of children and adolescents from different global regions fail to meet this guideline.
Excessive screen time has been linked to increased sedentary behavior, physical inactivity, unhealthy eating, and reduced sleep duration and quality. Existing evidence indicates that prolonged screen time can increase the likelihood of excess body fat accumulation in childhood.
Reduced physical activity due to excessive screen time can potentially influence cardiorespiratory fitness, which is the ability of the cardiac and respiratory systems to deliver oxygen to the muscles for energy production during physical activity. Reduced cardiorespiratory fitness, on the other hand, can contribute to less favorable adiposity and metabolic profiles.
Considering these bidirectional associations, researchers from the First Affiliated Hospital of Ningbo University, China, along with their collaborators, conducted a study to investigate the relationship between screen time and obesity-related metabolic indicators in childhood, as well as the impact of cardiorespiratory fitness on this association.
School-based study measured fitness, fat distribution, biomarkers
The study included a total of 1,286 third-grade students from six schools in Ningbo. Participants’ cardiorespiratory fitness was assessed using the 20-meter shuttle run test. Information on screen time, physical activity, and diet quality was obtained from self-reported questionnaires.
The participants were also assessed for anthropometric measurements, body composition, and blood pressure. Fasting blood samples were collected for biochemical examinations.
More screen time linked to higher body fat
The study analysis, adjusting for sex, age, maternal education level, physical activity, and diet, indicated that higher screen time is significantly associated with increased visceral fat accumulation, body fat mass index, and body fat percentage, and with lower cardiorespiratory fitness and slightly lower blood levels of HDL-C.
Considering the recommended guidelines, the study found that participants with more than two hours of daily screen time exhibit significantly increased visceral fat, fat mass index, and fat percentage, and significantly reduced cardiorespiratory fitness compared to those with less than two hours of daily screen time.
The mediation analysis revealed that cardiorespiratory fitness explains 66.6 % of the association between screen time and visceral fat, 67.5 % of the association with body fat mass index, 65.1 % of the association with body fat percentage, and a smaller proportion (22.6 %) of the association with HDL-C, indicating a more modest metabolic association compared with adiposity outcomes.
Reducing screen time and boosting fitness may improve outcomes
The study highlights the significant negative impact of higher screen time on measured adiposity indicators and selected metabolic markers in Chinese primary school–aged children. Importantly, the study suggests that higher cardiorespiratory fitness may attenuate part of the adverse adiposity-related profile associated with excessive screen time in this population.
Several factors previously reported in the literature have been linked to screen time and childhood obesity. It is known that children consume a significant proportion of their daily diet while watching screen media. In such scenarios, prolonged screen time can also extend their eating duration or distract them from the feelings of fullness, potentially promoting higher energy intake.
During screen time, children are exposed to advertisements for unhealthy foods, which can further affect their dietary preferences and choices. Furthermore, the blue light emitted from screen devices can delay sleep onset and affect sleep quality, which can indirectly contribute to weight gain and adiposity-related metabolic changes.
The study provides clear evidence about the mediating effect of cardiorespiratory fitness on the association between screen time and obesity-related indicators, particularly measures of visceral and total body fat, among children. An optimal cardiorespiratory fitness level, which indicates good cardiovascular health, is known to improve adverse physiological states associated with obesity, including chronic low-grade inflammation, oxidative stress, and mitochondrial dysfunction.
These observations suggest that unfavorable adiposity patterns and related metabolic markers in childhood may be improved by promoting physical activity levels and improving cardiorespiratory endurance among children.
Overall, the study highlights the need for developing comprehensive health promotion strategies that integrate screen time reduction and encouragement of physical activity to support healthier body composition and metabolic profiles in childhood.
The study included Chinese third-grade school students, which may restrict the generalizability of its findings to other populations or age groups. Moreover, because of the cross-sectional design, the study could not determine the causality of observed associations. Future studies should investigate the underlying mechanisms driving the effect of screen time on adiposity and related metabolic indicators to develop more effective intervention strategies.
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