Study On Sedentary Behaviors Among Chinese Urban Children And Adolescents

1. BackgroundThe deleterious effects of insufficient physical exercise on health of all populations have long been recognized among all countries. Many countries have published physical activity guidelines of all age groups and put great effort to promote moderate to vigorous physical activities. However, according to World Health Organization, among people older than 15 years old, approximately 31% of the population were not sufficiently physically active. Physical inactivity had cost 5.3 million premature deaths per year. Physical activity epidemiology start to shift the research focus from exercise activity towards PA of all domains, such as domestic, workplace and transport PA. With the progress of urbanization and technology advancement, human are freed from the labor burden of housework and workplace. For the past century, the overall physical activity level has dropped tremendously and sedentary lifestyle has become dominant of everyday life. Compared with other age groups, children and adolescents should be the most active group for the most available opportunities for physical activities such as games, school sports and extracurricular activities. However, as more types of media entertainment become accessible and available, children and adolescents are also becoming sedentary. A multi-country study revealed that the average time of children’ sedentary behavior is 4-8 hours. Chinese children’ sedentary behavior has also increased for the past 10 years and in 2008, among children between age 6 to 17,29.4% of the students spent 3 hours on sedentary behaviors during non-school hours. American and Canadian Pediatric Associations all have recommended that children should not engage in more than 2 hours of screen time per day.Clinical and epidemiology studies were conducted to investigate the link between sedentary behaviors and multiple health outcomes including all-cause mortality rate, cardiovascular diseases, colon cancer, metabolic syndrome and overweight and obesity among adults. In children, the negative effects of sedentary behavior on fitness, weight gain, overweight and obesity, psychosocial health and academic achievement have also been studied. In both developed and developing countries, childhood obesity is a serious health issue and reducing sedentary behaviors was an important strategy to fight against obesity. Childhood obesity is the outcome of both genetic and environmental influence, and its mechanism is very complicated. Many researchers proposed that among children, sedentary behavior led to excessive weight gain by interfering with sleep, replacing physical activity time and introducing snacking and unfavorable diet through media commercials. However those theories should be closely examined. By studying the relationships between sedentary behaviors and sleep, snacking and exercise, we should be able to better understand the possible mechanism between sedentary behavior and obesity.As a new study topic, previous studies have focused on TV viewing as a major surrogate of sedentary behavior. Such representation could be problematic considering the multivariate nature of children’s sedentary behaviors especially when tablet computers and smart phones are becoming popular. From public health perspective, to fully understand the possible correlates of screen time behaviors could help to effectively reduce children’s screen time. However such evidence in China is missing and urgently needed.2. GoalThis cross-sectional study aims to describe the recent epidemiology of sedentary behavior and, to examine the correlates of individual, socio-demographic and home screen environment with prolonged ST in adolescents residing in two Chinese cities with different degrees of urbanization. The relationships between sedentary behaviors and sleep, snacking, and exercise are examined. The clustering patterns of these behaviors and their associations with socio-economic indictors are also explored.3. Objectives and method3.1 To describe the time distributions of all types of sedentary behaviors across grade 4 to grade 8 and to compare the screen time of adolescents in two cities with different degrees of urbanization. Questionnaires were administered to both students and parents. Time spent on sedentary behavior outside of school hours on weekdays and weekends were asked.3.2 Based on social ecological model of sedentary behavior and concepts from social cognitive theory, individual, socio-demographic and home environment correlates of recreational screen time were examined. Suggestions to the school health and family health promotion were made.3.3 The relationship between sedentary behaviors and sleep (duration and quality), snacking, and exercise are each examined. Clustering patterns of obesogenic behaviors and related socio-demographic factors are explored.4. Main results4.1 The average durations of total sedentary time among elementary students (grade 4 and 5) were about 4 hours for weekday and 6 hours for weekend; among secondary students (grade 6,7 and 8), the average sedentary time were about 4 hours for weekday and 7 hours for the weekend. Homework is the dominant sedentary behavior, watching TV is the most prevalent screen behavior. The age and sex differences were observed on weekend day when boys and secondary students are more sedentary and heavier users of screen devices compared with girls and elementary students respectively. Compared with peri-urban peers, inner-city adolescents were more likely to use new technologies such as computer playing for boys and mobile phone playing for girls.4.2 More than three quarters of the parents reported more than 2 hours’screen time per day and more than one third of the students reported no family rules of screen time. There were more than half of the students that reported screen devices in the bedroom. Among all potential correlates, father’s education, mother’s TV time, individual attitude, family eating in front of TV, screen devices in the bedroom were found strongly associated with screen time. The relationship between number of electronic devices and screen time were moderated by agreement between parents and students.4.3 Among all types of sedentary behaviors, more time spent on homework and mobile phone playing was strongly associated with shorter sleep duration and later bed time, and worse sleep quality among older children. Screen behaviors were more predictive of snacking behavior of unhealthy food. Co-viewing behavior and new technologies such as computer playing and mobilephone playing were found correlated with unhealthy snacking. Weak correlations were observed between sedentary behaviors and exercise time. Four-cluster solution was indentified to examine the clutering patterns of obesogenic behaviors:sedentary behavior, sleep, snacking and exercise.5. Conclusions and further recommendations5.1 Boys and secondary students were more likely to be more sedentary and hearvier users of screen devices. Different preferences of screen entertainment were observed between boys and girls. School health education should target people at risk and involve instructions on how to make wise choices of screen devices and reasonable time limits.5.2 School health programs that intend to reduce children’s screen time should also involve parents, especial those on behavioral change. Key messages such as removing screen devices from bedroom and dinning area, enforcing family rule on screen time and limit one’s own screen behavior should be communicated to parents.5.3 The co-existence of sedentary behavior and exercise relect the different natures of the two behavior and future interventions or health promotions should target both simutanously. Snacking and sleep behaviors were more clustered with sedentary behaviors than exercise and had similar socio-demographic correlates. Lifestyle interventions could possibly target at those behaviors at the same time.