Artigos

Introduction
Excessive exposure to sedentary behaviors (SB) has been considered a risk factor for health in different cycles of life, including in adolescents 1, being associated with obesity 2, cardiometabolic risk factors 3, cardiovascular diseases, diabetes 3, depressive symptoms, anxiety symptoms, low self-esteem, suicidal ideation, loneliness, stress and psychological suffering4. Children and adolescents who spend more than two hours a day in SB are more likely to be overweight, have higher levels of cholesterol, smoke and have poor physical condition as adults 5,6.
Global recommendations and proposals in several countries suggest that children and adolescents should limit the time they spend per day in SB, particularly in recreational activities in front of the screens7, in addition to practicing at least 60 minutes of physical activity per day on average; however, the evidence is insufficient to quantify a SB7 threshold.
The effects of changes in social organization and unplanned urbanization of cities have contributed to the increase in time spent in SB, increasing the time spent sitting at work and while commuting. In addition to these factors, the spread and mass use of electronic devices, digital resources and applications and social networks have contributed to a wide digital/virtual transition. Television (TV), which previously was the only screen activity for most teenagers, now competes with computers, smartphones, tablets, and video games, which all contribute to the increase in time spent in sedentary behavior, especially in free time8. Even though access to digital technology in low-income and lower-middle-income countries is not massive compared to that observed in high-income countries, it is still occurring. For example, data from the 2018 National Survey by Household Samples9 in Brazil showed that less than half (41%) of the population had a computer and 12% had a tablet. However, 79.4% reported using the internet and 99.2% of these reported that a cell phone was used for this purpose9.
The time people spend awake has been increasingly occupied with sedentary behaviors: computer use, social networks, communication apps, games, teaching apps, sitting in the classroom, commuting from one place to another, and watching TV10. Studies show that teenagers occupy on average about 9 hours of their day in SB11 and 7 hours in recreational media (screen time), of which 2.5 hours are spent watching TV12,13. Data from the National Adolescent Health Survey (PeNSE) showed that 78% of adolescents spent more than 2 hours watching TV on normal weekdays, and 56.1% spent more than 3 hours watching TV, using a computer, playing video games or other seated activities 14.
Despite the solid body of evidence indicating that the proportion of adolescents exposed to SB is high15, and that there is an increase in other types of SB16, there are few studies evaluating the temporal trend of excessive TV exposure separately from other SB, especially in Brazil. Brazil has been going through an economic and social evolution since the last decade, with a better distribution of income in the population and in turn an increase in the purchasing power (acquisition of refrigerator, TV, computer, cell phone, among others) in the general population17. Over the last 10 years there have been changes which have had an impact on the time adolescents spend in SB: although there are indications that some SBs are in the process of declining in the population, the time spent sitting throughout the day has been increasing due to the insertion of new habits into daily life such as the use of cell phones, video games, computers, social networks and communication applications14. Despite these changes, studies with representative samples that assess the temporal trend of excessive time watching TV and other SB over time in adolescents aged 14 to 19 years, especially in low- and middle-income countries, are scarce.
Thus, the objective of the study was to describe the temporal trend of excessive exposure to TV and SB and to analyze the relationship of high exposure to sedentary behavior in different sociodemographic groups in a representative sample of adolescents aged 14 to 19 years of the Pernambuco state public education network from 2006 to 2016.

Method
This is a temporal trend study based on a data analysis of the “Atitude” research project – “Practice of Physical Activities and Health Risk Behaviors in High School Students in the State of Pernambuco: A Temporal Trend Study (2006-2011-2016)”. This project was approved by the Ethics Committee for Research with Human Beings at the University of Pernambuco (Opinion No. 1630.937).
The target population was limited to students enrolled in public high schools in Pernambuco. The number of students enrolled in these schools ranged from 367,813 in 2011 to 288,770 in 2016, respectively representing 88.9% and 88.1% of students enrolled in secondary education throughout the state of Pernambuco. Next, the following parameters were adopted in calculating the sample size: confidence interval of 95%, prevalence of 50% (this prevalence value was chosen because it is a study with multiple risk behaviors, and because it produces the highest expected prevalence for the same maximum acceptable error), maximum acceptable error in 2006 was 3 percentage points, and 2 percentage points in 2011 and 2016. A design effect was adopted (deff) equal to 4 in 2006, and equal to 2 in 2011 and 2016. The minimum sample size was increased by 20% every year to compensate for possible losses and/or refusals. The number of schools selected for the study was 76, 86 and 77 in 2006, 2011 and 2016, respectively.
A total of 6,031 adolescents were interviewed in 2006, while 6,845 and 6,338 were included in the 2011 and 2016 surveys, respectively. Adolescents outside the age group 14-19 years old and those who did not report valid data for sedentary behavior were excluded. Thus, data from 4,191, 6,254 and 5,930 adolescents were analyzed in the three surveys, respectively (Figure 1). Adolescents with mental disabilities who were unable to complete the questionnaire or adolescents who missed the data collection day were excluded from the study.
A double-stage cluster sampling process was used, with the first cluster being the school and the second the class. The sampling took into account the sizes of schools, as follows: size I (small) – less than 200 students; size II (medium) – 200 to 499 students; and size III (large) – more than 500 students. Students in the 2006 and 2011 surveys were grouped according to the study period: day and night. Students enrolled in the morning, afternoon and full-time shifts were grouped into the “day shift student” category.
Data were collected through the “Global School-based Student Health Survey” (GSHS) questionnaire proposed by the World Health Organization (WHO, 2005). This questionnaire was translated and adapted for this study, with reproducibility of the questions with a Kappa agreement index ranging from 0.62 to 0.80. The questionnaire was applied in the classroom without the presence of teachers through the collective interview technique, in which the researcher read the question and waited for the adolescents to respond.
Training was carried out with the collection team members before beginning the data collection in the three surveys to standardize the questionnaire application and carry out anthropometric and hemodynamic measurements. The same protocol was used to collect data from the three surveys.
Two indicators of overexposure to SB (>2 hours/day)18,19 were analyzed: i) overexposure to TV (time watching TV on school days (Monday to Friday) and on weekends (Saturday and Sunday). The combination of these variables was categorized into ? 2 hours and > 2 hours a day; and ii) excessive exposure to SB (except TV) (time spent sitting, talking with friends, playing cards or dominoes, talking on the phone, driving or as a passenger, reading or studying and time spent using a computer and/or playing video games?). The variable was also categorized into ? 2 hours and > 2 hours a day.
Excessive exposure to TV in the 2006 and 2011 surveys was categorically measured for both the week and the weekend. A combination of weekday and weekend results was performed for results purposes, considering ? 2 hours and > 2 hours a day when analyzing weekdays and weekends together. Behavior was continuously assessed in the 2016 survey, and subsequently categorized in the same way.
Excessive exposure to SB (except TV) was not assessed in the 2006 survey, while excessive time spent in SB (except TV) was categorically measured in 2011. Such behavior was continuously assessed in the 2016 survey, and later categorized into ? 2 hours and > 2 hours.
The sociodemographic factors evaluated were age group (14-15 years; 16-17 years; 18-19 years), maternal education (? 7 years, 8-10 years, 11 years, > 12 years or more), area of residence (urban, rural), worked (yes, no), has a computer connected to the internet (yes, no), high school grade (1st, 2nd or 3rd), shift (day (morning and afternoon), full-time, night).
The sampling plan (sampling by clusters, multiple stages) was considered in all statistical analyses incorporating the prefix “svyset” into the syntax, a resource available in Stata. Descriptive analysis included absolute and relative frequency distribution. Differences in the prevalence of excessive exposure to TV and SB between the data collection waves were tested through the intersection of 95% confidence intervals (95%CI).
Binary logistic regression was used to assess the odds ratio of overexposure (no = 0 and yes = 1) to TV comparing the year 2016 to 2006 and the odds of overexposure to SB (except TV) comparing the year from 2016 to 2011. Binary logistic regression was also used to analyze whether demographic factors were associated with excessive exposure to these behaviors during this period. An odds ratio equal to 1.0 reflects stability in excessive exposure to sedentary behavior over the 10-year period; values between 0 and 0.99 indicate a decrease in the chance of having excessive exposure to sedentary behavior over time; results above 1.0 show an increased chance of having excessive exposure to sedentary behavior over time. All analyzes were stratified by gender. The variance related to clusters (region and school) was considered in the regression models, and the intraclass correlation coefficient (ICC) of each model was calculated. The ICCs of both clusters were all less than 3%.

Results
Differences in the sample profile were observed between the three surveys: an increase in the proportion of adolescents aged 16 to 17 years old (48.5% in 2006 to 58.7% in 2016), of mothers with higher education (6.4% in 2006 to 16.6% in 2016), and computer availability at home (10.7% in 2006 and 58.9% in 2016). Most adolescents in all surveys were female (ranging from 59.8% to 55.2%) and lived in urban areas (approximately 80%). The proportion of students with a computer at home increased in both genders compared to 2006 and 2016 (Table 1): 13.1% to 64.0% in boys; and from 9.1% to 54.6% in girls.
Excessive exposure to television
The prevalence of overexposure to TV decreased by 23.0 percentage points in 10 years (2006-2016): 79.1%; 95%CI: 77.8-80.4 vs. 56.1%; 95%CI: 54.7-57.5. The decrease in boys was 28.2 percentage points (81.3%; 95%CI: 79.3-83.2 vs. 53.1%; 95%CI: 51.0-55.2) and in girls it was 19.2 percentage points (77.7%; 95%CI: 76.0-79.4 vs. 58.5; 95%CI: 56.6-60.4) (Figure 2). Over the 10 years of the analyzed period, the chance of an adolescent having excessive exposure to TV in 2016 compared to 2006 was 0.49 (95%CI: 0.45-0.53) in males and 0.62 (95%CI: 0.58-0 .66) in females.
Table 2 shows the prevalence of excessive exposure to TV time in each survey based on sociodemographic characteristics and stratified by gender. The prevalence of excessive TV time in both genders decreased in all sociodemographic subgroups analyzed (dwelling area, age, occupation, owning a computer, maternal education, school shift and adolescent grade level). Teenagers of both genders who had a computer and studied full-time had a greater magnitude of reduced excessive TV time than those who did not have a computer and studied during the daytime, respectively. In addition, adolescents of both genders who were 14 to 15 years of age and those who lived in urban areas also had a greater magnitude of reduced excessive exposure to TV time when compared to 18 to 19 years of age and those who lived in the countryside. There was a greater magnitude of reduced excessive exposure to TV time among girls for those who worked compared to those who did not work (Table 2).
Excessive exposure to sedentary behavior (except TV)
The prevalence of excessive exposure to SB (except TV) increased by 15.5 percentage points in 5 years (62.7%; 95%CI: 61.5-64.0 vs. 78.2%; 95%CI: 77.1- 79.4). The increase in boys was 15.4 percentage points (66.9%; 95%CI: 64.9-68.8 vs. 82.3%; 80.7-83.9), while the increase in girls was 15.3 percentage points (59.8%; 95%CI: 58.2-61.5 vs. 75.1%; 95%CI: 73.5-76.7) (Figure 2). The chance of an adolescent having excessive exposure to SB (except TV) in 2016 compared to 2011 was 2.36 (95%CI: 2.04-2.73) in males, and 2.07 (95%CI: 1.84-2.32) in females.
Table 3 shows the prevalence of overexposure in SB (except TV) in the 2 surveys (2011 and 2016) for the different sociodemographic characteristics stratified by gender. The prevalence of excessive time spent in SB (except TV) increased in both genders, regardless of sociodemographic characteristics (zone of residence, age, occupation, owning a computer, maternal education, shift and school grade). The magnitude of the increase in both genders was greater in rural residents and in those who studied full-time. The magnitude of the increase in excessive time in SB (except TV) in girls was greater in those who had a computer compared to those who did not (Table 3).


Discussion
The results of the present study revealed that the prevalence of excessive exposure to TV showed a significant decline for adolescents of both genders in 10 years, but slightly higher in males; in contrast, excessive exposure to SB (except TV) increased in both boys and girls in 5 years. Having a computer and studying full-time showed a greater magnitude of reduced excessive time spent watching TV in both sexes. Being younger and living in the urban area also showed a greater magnitude of reduced excessive exposure to TV time in boys when compared to being older and living in rural areas. This result was also verified in girls who worked. The increase in overexposure in SB (except TV) magnitude was greater in rural residents and those who studied full-time in both genders.
Over the course of 10 years, it was found that the prevalence of excessive TV exposure decreased, reinforcing the phenomenon that has been observed in other studies such as a survey conducted in the United States by the National Health and Nutrition Examination Survey (NHANES), in which there was a significant decrease in the average TV exposure per day over time. Boys showed the greatest reduction in the average time exposed to TV, from 2.2 hours of TV exposure per day to 1.6 hours20. The decrease in the average number of hours per day of TV exposure between 2002 and 2010 in other western countries was 18.6 minutes for girls and 24.0 minutes for boys19,20. The prevalence of young people in Brazil who watched TV for two hours or more a day between 2001 and 2011 decreased from 76.8% to 61.5%23.
In contrast, the prevalence of excessive exposure to SB (except TV) increased in adolescents in Pernambuco. Recent findings on total screen time using data from 2000 to 2010 among teenagers in the Czech Republic found a decrease in TV time which was replaced by an increase in computer use24. There was an increase in the prevalence of adolescents who used the computer and/or video game for two hours or more a day in the southern region of Brazil, going from 37.9 to 60.6%23.
This scenario indicates that the occupation of free time of adolescents watching TV has been decreasing and that this behavior does not represent the exposure of adolescents to SB, especially in isolation16. Despite this finding, it is noteworthy that the time watching TV is a sedentary behavior with particular implications for health and other behaviors, such as the consumption of unhealthy foods in front of the TV, violent behavior or certain behavior patterns disseminated in programs, advertisements which seek to increase unrestrained consumption, in addition to being associated with less PA practice time and affecting social relations between people. Although its measurement does not reflect sedentary behavior in general or screen time, studies which intend to assess the implications of watching TV should consider the measurement of this behavior.
The use of digital media, including interactive and social media, has grown substantially over the last decade. Traditional media, such as TV and radio, have been replaced by new technologies which promote interactive and social engagement and allow teenagers instant access to entertainment, information, knowledge and especially social contact25. Digital technologies that promoted greater exposure to sedentary behavior in high-income countries 26,27 were introduced in developing countries in recent years 28. The proportion of households with internet access in Brazil increased from 15% to 54% in 10 years (2006-2016). In addition, 13% of internet users over 10 years of age accessed the internet daily in 2006, while this proportion rose to 86% in 201629. This transformation in developing countries, including Brazil, called structural transformation, is defined as the transition from an economy of low productivity and labor-intensive economic activities to greater productivity and skill-intensive activities30. The speed of this transformation is driven by technology, whose main representative is the smartphone and with it the connections to social networks. For example, a total of 19.2% of teenagers between 10 and 14 years old and 35.0% of teenagers between 15 and 17 years old had their own cell phone in Brazil in 2005, while this number increased to 54.1% and 80.8% in 2014, respectively31.
Thus, the massification of digital media, the use of social networks, chat applications, exchanging messages on the network, the evolution of mobile phones with the availability of electronic games on the network, the possibility of browsing the Internet, low-cost film, tv series and documentary platforms and online commerce are all perceived, in such a way that these devices are being or are becoming increasingly popularized, covering all social levels. Adolescents started to value these means of fun, connection and interaction in their free time, leading to an increase in SB (except TV). The internet and the use of digital media have become one of the main means used by teenagers for social inclusion, allowing for quick, easy and comprehensive socialization. Adolescents virtually gather around common interests, inserting themselves in groups, communities and strengthening the feeling of belonging to their peers32.
In addition to other important factors such as less leisure spaces, insecurity and long periods of commuting, contributing to the increase in time spent in sedentary behavior, there is also the modification of social organization, stimulation of consumption and the digitization of the world. It is clear from the present study that changes based on the incorporation of media and social networks in adolescents’ lifestyles over the years present a relevant contribution to the increase in the total time spent in sedentary behavior. More modern facilities, presence of electricity and internet contribute to replacing physically active tasks for a longer time browsing social networks and playing video games 33. Furthermore, the chance that a teenager who had a computer at home of being exposed to excessive sedentary behavior was greater due to the ease of access to social networks, online games, and general use of digital media was expected in a period of 5 years.
The way in which sedentary behavior was measured and operationalized in this study needs to be highlighted as a limitation. The questions used in the three surveys to measure sedentary behavior, despite approaching the topic in a similar way, were not the same; however the answers from the 3 surveys were operationalized in the same way. Using SB (except TV) as the measure did not cover all activities in SB, however our measure reflects the time in SB relatively well, since the most frequent activities were addressed.
This study has strengths which should be taken into account: it is one of the only studies with 3 surveys carried out on representative samples of public-school students in a Northeastern state, and it can be carefully extrapolated to the national level and to other developing countries. In addition, these results may serve as support for future public health strategies aimed at Brazilian adolescents, as they describe a growing trend in the prevalence of excessive exposure to SB in adolescents. Highlighting the important role of the school setting in the reduction of sedentary behavior among adolescents since schools represent an unique social context for health promotion among youth. Particularly for adolescents from low-income families, who are often overlooked in health care promotion programs. In fact, schools are considered the ideal setting for health promotion programs among youth considering that the vast majority of children and adolescents, even in low-income countries, are enrolled in the educational system, and that schools already have installed infrastructure 34. Furthermore, it has been shown that interventions in the school setting, such as implementing low-complexity strategies (e.g., additional physical educational classes, workshops for physical education teachers), can decrease time dedicated to sedentary behaviors and enhance time spent in physical activities 35,36.
The present study showed that there was a change in the time trend in excessive exposure to TV over 10 years, with a decrease of approximately 23 percentage points being observed; in contrast, there was an increase of 15 percentage points in excessive exposure to SB (except TV) in 5 years. These results suggest that watching TV, although clearly an important sedentary behavior and still having a high prevalence, does not reflect the total time or does not explain the variation in time spent in SB in adolescents very well.

Acknowledgments: Acknowledgments for their support National Council for Scientific, Technological Development (CNPq) National Council for the Improvement of Higher Education (CAPES) and Foundation for the Support of Science and Technology of the State of Pernambuco (FACEPE).
Funding Source: This study was supported financially by National Council for Scientific, Technological Development (CNPq; grant 432144/2016-1).
















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