Sedentary Behavior in Young People and Related Complications: An International Challenge

There has been special attention targeted on sedentary behavior in recent years, in both academic and popular press aspects (1). In addition, technological advances and new factories have resulted in the migration of many people from rural areas to urban areas with much less mobility compared to farming. Nowadays, people could spend more than 60% of their 16-hour waking time in sitting situation by watching TV, sitting in front of computers at work and home, speaking on the phone as well as sitting in a car to go to the workplace. Furthermore, children may not walk to their neighborhood school, but may be transported to more distant schools. After school, they prefer to spend a lot of time playing video games or talking on the phone instead of playing outside with their friends. In addition, people easily order their needs via the internet, which will be delivered at their home (2). Nowadays, exposure to digital media in all family life has also been increasing (3). Therefore, many of adolescents did not achieve enough moderate weekly physical activity and would thus continue to fail to achieve this activity into the adulthood (4).

British children, for example, have regular access to an average of five different screens at home by the age of 10. For instance, in addition to the main family television, many young children may have their own bedroom TV as well as portable computer game consoles (5). Moreover, almost one in three American infants may have a TV in their own bedroom, and about half of all infants may watch TV or DVDs for at least two hours per day (5). Furthermore, children may engage in two or more types of screen viewing at the same time routinely; for example, TV and laptop (6). The revolution of electronic media as well as rising automotive transport, has indeed resulted in more sitting time. Therefore, the major part of waking hours could be attributed to sedentary behavior (7). Consequently, increasing opportunities for spending time in sedentary behavior, will increase chronic diseases in parallel too, which is a basis for suggesting the hypothesis of increasing risk of chronic diseases with spending too much time in sedentary behavior (8, 9)

Sedentary behavior is usually considered as activities, which require a little or even no additional energy expenditure more than resting metabolic rate (10, 11), especially during waking hours with activities like sitting or lying down (12). Generally, the activities could be divided into two groups: leisure-time activities such as TV viewing, playing video games and leisure-time computer use as the first group, and sitting during school or work time as the second group (13). In fact, many people around the world would spend a lot of their time in sedentary behavior mainly because of new modern technologies (14). This may largely increase the risk of chronic diseases (11). Excessive sedentary behavior could be associated with some health events such as cardiovascular disease mortality, premature all-cause mortality and obesity (11). Such excessive sedentary behavior in young population will indeed have a harmful effect on their health (15). Therefore, there have been many educational efforts focusing on decreasing of sedentary behavior from an early age (16). Young people’s daily routine schedule usually consists of many sedentary activities, such as sitting in classes at school, studying and leisure time, which all could be the best target for preventive strategies among young population (15, 17).

The younger population may indeed spend a lot of time in sedentary behavior. Children and adolescents could spend about 6 to 8 hours daily watching TV, playing video games and using computers on average with good evidence to confirm the association of TV viewing and obesity, increasing fat mass and higher body mass index (BMI) (18), as well as decreasing academic achievement (19). Moreover, there are new types of sedentary behavior such as using new media devices like cell phones, laptops and tablets, which its usage is going to increase among children and adolescents, although its related risk with obesity has not been confirmed yet (20). Furthermore, several substantial associations between screen time and unhealthy behaviors, psychosocial problems, being overweight and having low general self-efficiency (GSE) have been reported. Compulsive and excessive internet use was also significantly associated with unhealthy behaviors and undesirable health outcomes. Therefore, there must be special attention to screen time and associated unhealthy behaviors among adolescents in future studies (21). Furthermore, there is some evidence that watching television could be a reinforcing activity which may consume a huge part of a child’s leisure time and might be associated with an increase in the prevalence of children’s obesity (22-24). Generally, research has approved the following issues: a) TV viewing could be the main sedentary pastime in many adolescents; b) on weekends, the time of sedentary activities would be 2-3 times greater than weekdays; c) while girls mostly prefer to search on the internet, boys prefer to spend more time for playing electronic games; d) about 44% of adolescents may have a TV set in their own bedroom and most of them did not comply with public health recommendations for correcting their sedentary behavior (24).

Screen time was in fact associated with less desirable food choices, especially among overweight/obese children (25). In addition, there was an association between children's dietary intake and screen time, which might be due to their weight status or maybe other factors such as food availability and appetite that could be linked to their weight situation. Therefore, health care professionals involving the treatment of overweight children should consider screen time as well and encourage children and adolescents to have screen time less than 2 hours per day (25). Considering the effect of sitting time (independent of physical activity) on all-cause mortality risk, the efforts to reduce sitting time could play a substantial role in promotion of lifestyle to active one, and further potential declining of premature mortality prevention across the world (26).

Research has indeed shown that sitting time might be responsible for about 3.8% of all deaths worldwide; thus, strategies for prevention among target population must focus on main determinants of the entire daily activities, which may affect to reduce millions of deaths across the world (26). In addition, it has been reported that higher risk of all-cause mortality may be associated with greater daily sitting time; thus, moderate-to-vigorous physical activity might be attenuate this association (27). Generally, each hour of sitting time per day may be associated with about 2% increase in all-cause mortality risk, considering the protective effects of physical activity. Similarly, the risk could be increased significantly when sitting time would be more than 7 hours per day (27). Moreover, the prevalence of obesity, measured by BMI, has substantially increased in recent decades (28) especially among children and adolescent (about 17% among US children) (29). This fact is very important due to increased likelihood of developing metabolic and cardiovascular problems in later life, among children with higher BMI (30). Many serious health problems during childhood could also be associated with obesity (31) which may lead to higher risks for stroke, cardiovascular disease, asthma, as well as some cancers lifetime (32). There is a hypothesis about increasing trend of obesity which focuses on sedentary behavior (33). In addition, findings of ecological studies have reported parallel increases in some important markers of sedentary behavior such as television sales and car ownership, with increases in BMI (9). It seems that the period of transition from childhood to adolescence could also be a substantial key period for increasing sedentary behavior (7). It has been confirmed that there is an association between sedentary behavior and greater increases in BMI at the 90th, 75th and 50th BMI percentiles of children and adolescents between ages 9 and 15 years, regardless of moderate-to-vigorous physical activity (MVPA). Efforts to prevent increasing sedentary behavior from childhood to adolescence can reduce the potential number of children and adolescents whom classified as obese (33). Both cross-sectional and longitudinal studies have reported an association between obesity and lower aerobic fitness in young people and spending too much time with sedentary behavior, particularly screen-based sedentary behavior (8). In addition, insulin sensitivity and clustered metabolic risk in young population were associated with more time spent in sedentary behavior cross-sectionally but not longitudinally (8). Moreover, there was no evidence for association between sedentary behavior and potential increasing of blood pressure and blood lipids in young people (8).

There is a debate if sedentary behavior and physical inactivity are the same or related to each other (34). In fact, sedentary behaviors could compete with physical inactivity, less activity as well as more energy expenditure (35). In addition, sedentary behavior and physical activity may be associated with metabolic and mental health during childhood and adolescence; thus, knowing the interrelationships between these two behaviors could help to promote interventional program design (36). It has also been found that increasing sedentary behaviors could have more influence on physical activity and energy intake than reducing sedentary behavior among non-obese youth. Furthermore, in some adolescents, any change in sedentary behaviors might be important for modifying energy balance to prevent obesity (37). It has been confirmed that sedentary behavior and physical activity in young people may have a negative and small association, which suggests inability of direct displacing of these behaviors one another (36). In addition, one of the most important periods to promote physical activity is transition time from adolescence to young adulthood, as well as reducing TV, computer, video games and cell phone use. Therefore, encouragement of current active adolescents to maintain adequate physical activity is necessary.

It has been recommended that preventive efforts are necessary throughout the life cycle, especially before adolescence, mainly among adolescents with low and declining physical activity and high frequency of TV and video viewing as well as computer/video game/cell phone use (4). Research has also shown that higher annual household income may be related to more intense, more daily sedentary time and less frequent weekly patterns of physical activity (38). In fact, there was an observed significant association between income and efficiently use of time for physical activity. In addition, individuals from high income group, may use their time more ‘wisely’ to have more vigorous intensity activity, but not light intensity activity and sedentary behavior; thus, this fact must be considered at the time of designing intervention programs (38). Moreover, sedentary behavior may increase from age 12 to 16 by light-intensity physical activity, which can be tracked over time. The spending time of continuous sedentary behavior which lasts 30 minutes or more could be an indicator of more prolonged sedentary behavior (39). It is worth mentioning that similar to sedentary time, physical inactivity could also be associated with all-cause mortality as well as many important noncommunicable diseases (40). It has also been estimated that about 31% of the world population may not have enough recommended physical activity (41). Moreover, the burden of disease attributable to physical inactivity was estimated that physical inactivity might be responsible for about 6-9% of all deaths worldwide (42).

Determinants of sedentary behavior should be identified as both individual and contextual factors such as interpersonal, build or physical environmental as well as policy determinants according to socio-ecological models of health behavior (43), and to develop efficient interventions for reducing sedentary time, it is necessary to investigate the determinants of sedentary behavior (44). In addition, it has been reported that sitting reduction strategies with consideration of increasing standing or stepping or both, might have some benefits for cardiometabolic health. In fact, standing could be the simplest alternative for sitting (45). It has also been suggested that reducing school day sitting time in adolescents could lead to substantial improvements in apoB/apoA-1 ratio, but medium effect on total cholesterol, HDL cholesterol and total cholesterol/HDL ratio. In addition, cognitive function findings could also show a 6-month improvement in effective mental/attentional capacity of adolescents (46). Adolescents and children could then be motivated to bidirectionally shift their high-rate sedentary behaviors considering the fact that increasing sedentary behaviors may be associated with increasing in positive energy balance intake (37). In addition, in obese children, reinforcing a decrease in sedentary behaviors is associated with increases in physical activity (47). Reducing access to television is associated with prevention of obesity too (48). Clinical research has also shown that reducing a variety of sedentary behaviors including watching television may reduce obesity and increase the fitness as much as targeting physical activity (49). Conversely, reducing television is associated with a reduction in eating episodes (48). In addition, there has been a positive effect of short-term regular moderate-to-vigorous physical activity on human health and well-being (50). There is also evidence that implementation of activity workstations on college campuses could have some benefits on their health and wellbeing without negative effects on their academic performance (51). Thus, there could be some efforts to design sedentary behavior modules which can be commonly used in national and international surveys. however, there is no unique module in this regard. Therefore, the new designed module has been based on the best available evidence that could be modified to be suitable for the needs of individual surveys, its psychometric properties and other potential questionnaires, which are currently used in population health surveys (52).