ABSTRACT

OBJECTIVE

To describe the methodological characteristics of the studies selected and assess variables associated with sedentary behavior in Brazilian children and adolescents.

METHODS

For this systematic review, we searched four electronic databases: PubMed, Web of Knowledge, LILACS, SciELO. Also, electronic searches were applied in Google Scholar. A supplementary search was conducted in the references lists of the included articles and in non-indexed journals. We included observational studies with children and adolescents aged from three to 19 years developed in Brazil, presenting analyses of associations based on regression methods and published until September 30, 2014.

RESULTS

Of the 255 potential references retrieved by the searches, 49 met the inclusion criteria and composed the descriptive synthesis. In this set, we identified a great number of cross-sectional studies (n = 43; 88.0%) and high methodological variability on the types of sedentary behavior assessed, measurement tools and cut-off points used. The variables most often associated with sedentary behavior were “high levels of body weight” (in 15 out of 27 studies; 55.0%) and “lower level of physical activity” (in eight out of 16 studies; 50.0%).

CONCLUSIONS

The findings of this review raise the following demands to the Brazilian agenda of sedentary behavior research geared to children and adolescents: development of longitudinal studies, validation of measuring tools, establishment of risk cut-offs, measurement of sedentary behavior beyond screen time and use of objective measures in addition to questionnaires. In the articles available, the associations between sedentary behavior with “high levels of body weight” and “low levels of physical activity” were observed in different regions of Brazil.

Child; Adolescent; Sedentary Lifestyle; Risk Factors; Review

INTRODUCTION

Sedentary behavior represents activities of little movement, which occur with the body in sitting or reclining position, and present energy expenditure close to that observed in the resting state (< 1.5MET)¹1. Ainsworth BE, Haskell WL, Whitt MC, Irwin ML, Swartz AM, Strath SJ et al. Compendium of physical activities: an update of activity codes and MET intensities. Med Sci Sports Exerc. 2000;32(9 Suppl):S498-504. DOI:10.1097/00005768-200009001-00009^,5050. Pate RR, O’Neill JR, Lobelo F. The evolving definition of “sedentary”. Exerc Sport Sci Rev. 2008;36(4):173-8. DOI:10.1097/JES.0b013e3181877d1. Nowadays, it comprehends activities present in a big part of everyday life, whether in people’s leisure time (talking to friends, using the phone, watching television, using computers or videogames), in transit (driving, riding public transportation, standing up), or even in environments such as work and school, where people are exposed to longer periods sitting down. A growing body of evidence strengthens the consensus that sedentary behavior is a different domain from physical activity, no longer characterized by its absence, with its own related and determinant factors and implications for health¹⁰10. Cong YJ, Gan Y, Sun HL, Deng J, Cao SY, Xu X et al. Association of sedentary behaviour with colon and rectal cancer: a meta-analysis of observational studies. Br J Cancer. 2014;110(3):817-26. DOI:10.1038/bjc.2013.709^,3232. Ford ES, Caspersen CJ. Sedentary behaviour and cardiovascular disease: a review of prospective studies. Int J Epidemiol.2012;41(5):1338-53. DOI:10.1093/ije/dys078^,3535. Grontved A, Hu FB. Television viewing and risk of type 2 diabetes, cardiovascular disease, and all-cause mortality a meta-analysis.JAMA. 2011;305(23):2448-55. DOI:10.1001/jama.2011.81.

In children and adolescents, sedentary behavior has usually been represented by exposure to screen-related behaviors, which include measures (separate or unified) of time spent with television, video games, tablets, cell phones and computers⁵¹51. Pearson N, Biddle SJ. Sedentary behavior and dietary intake in children, adolescents, and adults: a systematic review. Am J Prev Med. 2011;41(2):178-88. DOI:10.1016/j.amepre.2011.05.002^,7070. Tremblay MS, LeBlanc AG, Kho ME, Saunders TJ, Larouche R, Colley RC et al. Systematic review of sedentary behaviour and health indicators in school-aged children and youth. Int J Behav Nutr Phys Act.2011;8:98. DOI:10.1186/1479-5868-8-98. These, in turn, represent only a fraction of the total time spent by young people with sedentary behaviors, excluding other sedentary activities such as time sitting at school and in transit, for example. However, despite this limitation, the Pesquisa Nacional de Saúde do Escolar(PeNSE – Brazilian National School-Based Health Survey) showed that the prevalence of adolescents exposed to at least two hours a day of television is high all over the country (78.0% in total, 79.2% in the female sex, and 76.7% in the male sex)⁴⁶46. Ministério do Planejamento, Orçamento e Gestão (BR); Instituto Brasileiro de Geografia e Estatística. Pesquisa de orçamentos familiares 2008-2009: antropometria e estado nutricional de crianças, adolescentes e adultos no Brasil. Rio de Janeiro: Instituto Brasileiro de Geografia e Estatística (IBGE); 2010..

A systematic review points out that two or more hours of television a day are associated with various harms to health such as high levels of body weight, decreased physical fitness, low self-esteem scores and worsening of student performance⁷⁰70. Tremblay MS, LeBlanc AG, Kho ME, Saunders TJ, Larouche R, Colley RC et al. Systematic review of sedentary behaviour and health indicators in school-aged children and youth. Int J Behav Nutr Phys Act.2011;8:98. DOI:10.1186/1479-5868-8-98. However, this evidence should be interpreted with caution, since it is heavily based on the results of cross-sectional studies conducted in high-income countries.

Although a recent study has identified a large number of Brazilian publications reporting associated and determinant factors of physical activity and sedentary behaviors in different stages of life⁵³53. Ramires V, Becker L, Sadovsky A, Zago A, Bielemann R, Guerra P. Evolução da pesquisa epidemiológica em atividade física e comportamento sedentário no Brasil: atualização de uma revisão sistemática. Rev Bras Ativ Fis Saude. 2014;19(5):529. DOI:10.12820/rbafs.v.19n5p529, it did not further develop what are the variables frequently associated with these two behaviors in childhood and adolescence. Identifying the factors associated with the adoption of these behaviors is crucial to recognize them and foster the development of preventive measures. It also enables expanding the evidence about the possible implications of long-term exposure to these behaviors for teenager health.

The objectives of this study were: (i) to describe methodological aspects used in Brazilian studies involving the types of sedentary behavior most often assessed, the tools used to assess it and the cut-off points adopted for its classification and (ii) to summarize the variables associated with sedentary behavior in Brazilian children and adolescents.

METHODS

This study is part of the project “Systematic review of determinants and factors associated with sedentary behavior in children and adolescents”, registered on the International Prospective Register of Systematic Reviews database (PROSPERO-CRD42014014107). Its report is in agreement with the Preferred Reporting Items for Systematic Reviews (PRISMA)⁴⁰40. Liberati A, Altman DG, Tetzlaff J, Mulrow C, Gotzsche PC, Ioannidis JP et al. The PRISMA statement for reporting systematic reviews and meta-analyses of studies that evaluate healthcare interventions: explanation and elaboration. BMJ. 2009;339:b2700. DOI:10.1136/bmj.b2700.

To compose the synthesis, we searched for scientific articles that adequately met the following criteria: (i) observational studies (cross-sectional, cohort and cases-control); (ii) developed in the Brazilian territory, regardless of their representativeness (local, regional, national); (iii) with results of associations based in regression methods; (iv) reporting measures of sedentary behavior, either by total or type-specific exposure (e.g., screen-related behavior), domain (e.g., leisure, transit, school) or a combination (e.g., time sitting in school and leisure), regardless if evaluated as exposure or outcome variable, and (v) involving child or adolescent samples in the range of three to 19 years of age, or mean age within this range. We have excluded studies that used the term sedentary as a synonym for lack of physical activity (or insufficient physical activity) or those related to special groups (e.g., people with hypertension and diabetes). Since this review was outlined with descriptive purposes and, since its inception, no meta-analysis has been planned, we decided to include separate publications in the same sample, as long as all the inclusion criteria were met.

Regarding the operational process, a researcher conducted the stages of reading and evaluating titles, abstracts and full texts, extracting data and making the synthesis. In view of the descriptive characteristic of this review, the risk of bias of each article was not assessed.

The relevant articles were searched in different ways. Four electronic databases were searched: PubMed, Web of Knowledge, LILACS and SciELO, using the terms and keywords: sedentary behavior OR screen time OR TV time OR sitting time AND factors OR correlates OR determinants AND Brazil OR Brasil AND infant OR child OR adolescent. Also, Google Scholar was searched, with the following search strategy:comportamento sedentário (sedentary behavior), tempo de tela (screen time) and Brasil (Brazil). To prevent the loss of relevant information, we conducted additional searches in the Lattes curriculum (lattes.cnpq.br) of some of the leading researchers on the topic, in the reference lists of the included papers and in non-indexed journals.

Data were extracted in a spreadsheet in which the information had been divided into three domains: (i) descriptive data (location of study, year of collection, sample size, age range, sex); (ii) methods (type of study, selection of participants, sampling unit, exposure, sedentary behavior assessment tool, regression model, adjusted variables and outcome measure) and (iii) results, retrieving the analyses of possible associations between sedentary behavior and variables grouped and organized into five sub-domains: harms to health (e.g., body weight, blood pressure and insulin resistance); environmental (e.g., place of residence); socioeconomic and demographic (e.g., sex, age, skin color and income); behavioral (e.g., sleep time, physical activity, consumption of fruits and vegetables); and occupational (e.g., study hours, work).

The results of the studies were classified into conditions or groups: (i) without statistically significant association (p > 0.05); or with statistically significant association (p < 0.05), either positive (ii) or negative (iii). Positive associations indicate that higher levels or greater amount of time in sedentary behaviors are associated with higher levels of the variable. Negative associations indicate that higher levels or greater amount of time spent in sedentary behaviors are associated with lower levels of the variable.

RESULTS

After exclusion of the duplicates among the four databases (n = 11), the procedure of systematic searches retrieved 255 references. After assessment of titles and abstracts and considering nine articles retrieved in references lists, 88 references were conduced to full text assessment. With 39 exclusions (no use of regression models: n = 18; adoption of the term sedentary behavior as absence of physical activity: n = 17; no assessment of the sedentary behavior: n = 2; age outside the range of three to 19 years: n = 1; research conducted outside Brazil: n = 1), were considered 49 articles for the descriptive synthesis (Figure).

In total, we observed 38 separate samples in the 49 articles that composed the synthesis, since some of them assessed the same samples (the states of Santa Catarina⁶³63. Silva KS, Nahas MV, Hoefelmann LP, Lopes AS, Oliveira ES. Associações entre atividade física, índice de massa corporal e comportamentos sedentários em adolescentes. Rev Bras Epidemiol.2008;11(1):159-168. DOI:10.1590/S1415-790X2008000100015^,6464. Silva KS, Nahas MV, Peres KG, Lopes AS. Fatores associados à atividade física, comportamento sedentário e participação na Educação Física em estudantes do Ensino Médio em Santa Catarina, Brasil. Cad Saude Publica. 2009;25(10):2187-200. DOI:10.1590/S0102-311X2009001000010 and Pernambuco⁶⁸68. Tassitano RM, Barros MVG, Tenório MCM, Bezerra J, Hallal PC. Prevalência e fatores associados ao sobrepeso e à obesidade em adolescentes, estudantes de escolas de Ensino Médio de Pernambuco, Brasil. Cad Saude Publica. 2009;25(12):2639-52. DOI:10.1590/S0102-311X2009001200011^,6969. Tenório MCM, Barros MVG, Tassitano RM, Bezerra J, Tenório JM, Hallal PC. Atividade física e comportamento sedentário em adolescentes estudantes do ensino médio. Rev Bras Epidemiol.2010;13(1):105-17. DOI:10.1590/S1415-790X2010000100010 and the cities: Joao Pessoa⁶¹61. Silva KS, Lopes AS, Silva FM. Comportamentos sedentários associados ao excesso de peso corporal. Rev Bras Educ Fis Esporte. 2007;21(2):135-41.^,6262. Silva KS, Lopes AS, Silva FM. Atividade física no deslocamento à escola e no tempo livre em crianças e adolescentes da cidade de João Pessoa, PB, Brasil. Rev Bras Ciênc Mov. 2007;15(3):61-70., Maringa¹³13. de Moraes ACF, Fernandes CAM, Elias RGM, Nakashima ATA, Reichert FF, Falcão MC. Prevalência de inatividade física e fatores associados em adolescentes. Rev Assoc Med Bras. 2009;55(5):523-8. DOI:10.1590/S0104-42302009000500013

14. de Moraes ACF, Adami F, Falcão MC. Understanding the correlates of adolescents’ dietary intake patterns: a multivariate analysis.Appetite. 2012;58(3):1057-62. DOI:10.1016/j.appet.2012.01.024

15. de Moraes ACF, Falcão MC. Lifestyle factors and socioeconomic variables associated with abdominal obesity in Brazilian adolescents.Ann Hum Biol. 2013;40(1):1-8. DOI:10.3109/03014460.2012.745900^-1616. de Moraes ACF, Carvalho HB, Rey-López JP, Beghin L, Kafatos A, Jiménez-Pávon D et al. Independent and combined effects of physical activity and sedentary behavior on blood pressure in adolescents: gender differences in two cross-sectional studies. PLoS One. 2013;8(5):e62006. DOI:10.1371/journal.pone.0062006, Pelotas²⁰20. Dumith SC, Hallal PC, Menezes A, Araújo CL. Sedentary behavior in adolescents: the 11-year follow-up of the 1993 Pelotas (Brazil) birth cohort study. Cad Saude Publica. 2010;26(10):1928-36. DOI:10.1590/S0102-311X2010001000009

21. Dumith SC, Garcia LMT, Silva KS, Menezes AMB, Hallal PC. Predictors and health consequences of screen-time change during adolescence – 1993 Pelotas (Brazil) birth cohort study. J Adolesc Health.2012;51(6):S16-21. DOI:10.1016/j.jadohealth.2012.06.025^-2222. Dumith SC, Gigante DP, Domingues MR, Hallal PC, Menezes AMB, Kohl HW. Predictors of physical activity change during adolescence: a 3.5-year follow-up. Public Health Nutr. 2012;15(12):2237-45. DOI:10.1017/S1368980012000948^,2424. Duquia RP, Dumith SC, Reichert FF, Madruga SW, Duro LN, Menezes AMB et al. Epidemiologia das pregas cutâneas triciptal e subescapular elevadas em adolescentes. Cad Saude Publica. 2008;24(1):113-21. DOI:10.1590/S0102-311X2008000100011, and Presidente Prudente²⁹29. Fernandes RA, Freitas Júnior IF, Cardoso JR, Ronque ERV, Loch MR, Oliveira AR. Association between regular participation in sports and leisure time behaviors in Brazilian adolescents: a cross-sectional study. BMC Public Health. 2008;8:329. DOI:10.1186/1471-2458-8-329

30. Fernandes RA, Christofaro DGD, Casonatto J, Kawaguti SS, Ronque ERV, Cardoso JR et al. Cross-sectional association between healthy and unhealthy food habits and leisure physical activity in adolescents. J Pediatr (Rio J). 2011;87(3):252-6. DOI:10.2223/JPED.2093^-3131. Fernandes RA, Christofaro DGD, Cardoso JR, Ronque ER, Freitas Júnior IF, Kawaguti SS et al. Socioeconomic status as determinant of risk factors for overweight in adolescents. Cien Saude Coletiva.2011;16(10):4051-7. DOI:10.1590/S1413-81232011001100010). The samples ranged between 276¹²12. Crispim PAA, Peixoto MRG, Jardim PCBV. Fatores de risco associados aos níveis pressóricos elevados em crianças de dois a cinco anos.Arq Bras Cardiol. 2013;102(1):39-46. DOI:10.5935/abc.20130227 and 109,104⁵⁶56. Rezende LFM, Azeredo CM, Canella DS, Claro RM, Casro IRR, Levy RB et al. Sociodemographic and behavioral factors associated with physical activity in Brazilian adolescents. BMC Public Health.2014;14:485. DOI:10.1186/1471-2458-14-485 participants, with a higher percentage of girls in 23 of them (60.5%). Despite the distinction between the number of articles included in the synthesis and the total number of samples found, we based all analyses of this review on the set of 49 included articles, respecting its descriptive character.

Also in Table 1, by geographic location, we observed a predominance of articles produced in the Southern region of the Country (n = 20; 40.8%), followed by the ones developed in the Southeast and Northeast, with 11 each (22.4% for each region). In this set, we point out two publications of national representativity, based on data from PeNSE, involving adolescents of all state capitals and the Federal District⁷7. Camelo LV, Rodrigues JFC, Giatti L, Barreto SM. Lazer sedentário e consumo de alimentos entre adolescentes brasileiros: Pesquisa Nacional de Saúde do Escolar (PeNSE), 2009. Cad Saude Publica.2012;28(11):2155-62. DOI:10.1590/S0102-311X201200110001^,5656. Rezende LFM, Azeredo CM, Canella DS, Claro RM, Casro IRR, Levy RB et al. Sociodemographic and behavioral factors associated with physical activity in Brazilian adolescents. BMC Public Health.2014;14:485. DOI:10.1186/1471-2458-14-485. Only eight articles had data collection deadlines prior to the year 2005 (16.3%), and sedentary behavior was the outcome variable in 13 articles (26.5%).

The synthesis of this review was based on 43 cross-sectional studies, three case-control studies⁴4. Balaban G, Motta MEFA, Silva GAP. Early weaning and other potential risk factors for overweight among preschool children.Clinics. 2010;65(2):181-7. DOI:10.1590/S1807-59322010000200010^,4141. Lippo BRS, Silva IM, Aca CRP, Lira PIC, Silva GAP, Motta MEFA. Determinants of physical inactivity among urban adolescents. J Pediatr (Rio J.). 2010;86(6):520-4. DOI:10.2223/JPED.2047^,5757. Ribeiro IC, Taddei JAAC, Colugnatti F. Obesity among children attending elementary public schools in Sao Paulo, Brazil: a case–control study.Public Health Nutr. 2003;6(7):659-63. DOI:10.1079/PHN2003473, and three studies from the Pelotas cohort²¹21. Dumith SC, Garcia LMT, Silva KS, Menezes AMB, Hallal PC. Predictors and health consequences of screen-time change during adolescence – 1993 Pelotas (Brazil) birth cohort study. J Adolesc Health.2012;51(6):S16-21. DOI:10.1016/j.jadohealth.2012.06.025^,2222. Dumith SC, Gigante DP, Domingues MR, Hallal PC, Menezes AMB, Kohl HW. Predictors of physical activity change during adolescence: a 3.5-year follow-up. Public Health Nutr. 2012;15(12):2237-45. DOI:10.1017/S1368980012000948^,2626. Enes CC, Slater B. Variation in dietary intake and physical activity pattern as predictors of change in body mass index (BMI) Z-score among Brazilian adolescents*. Rev Bras Epidemiol. 2013;16(2):493-501. DOI:10.1590/S1415-790X2013000200023 (Table 2). About the measurement of sedentary behavior, observations of screen time (n = 27; 55.1%) and television time (n = 16; 32.6%) exposures prevailed. The cut-off point most often used in the articles to characterize excess of time in sedentary behaviors was at least two hours a day, adopted in 16 publications (30.6%). It comprehends: screen time (n = 10); time watching television (n = 4); time using the computer (n = 1); or screen time (n = 1). Even if all the articles included have used questionnaires to assess sedentary behavior, there was great variation in the tools used. In 17 articles (34.7%), the authors did not report if the tool had been validated or, in the case of foreign tools, if it had been validated for use in Brazilian populations.

The articles presented analyses between sedentary behavior and 31 different variables (Table 3). Most of these have been classified as behavioral variables (n = 12). The large number of variables belonging to demographic or socioeconomic domains (n = 7) and harms to health (n = 6) is also noteworthy.

As for the number of articles and the frequency of associations between the measurement of sedentary behavior and the variables of one or more domains, the main result found was the positive association between high volumes of sedentary behavior and “high levels of body weight”, observed in 15 of the 27 articles that evaluated this relationship (55.5%). Most of the results that identified statistically positive associations between sedentary behavior and that variable were from studies that assessed screen behaviors, whether specific (such as television and computer) or total screen time. On the measurement effect of these studies, eight statistically positive associations were expressed by prevalence ratios, six by odds ratios and one by coefficient (β). We point out that two of those positive associations between higher volumes of sedentary behavior and “high levels of body weight” derive from longitudinal studies (one cohort and one case-control) (Table 3).

As a secondary result, 50.0% (eight of 16) of articles have shown statistically positive associations between high volumes of sedentary behavior and “low levels of physical activity”. As with the previous result, most of those studies evaluated sedentary behavior by screen behaviors (total, n = 4, and television, n = 3). By type of study, we observed two of those positive associations in the studies based on the 1993 Pelotas birth cohort^,2121. Dumith SC, Garcia LMT, Silva KS, Menezes AMB, Hallal PC. Predictors and health consequences of screen-time change during adolescence – 1993 Pelotas (Brazil) birth cohort study. J Adolesc Health.2012;51(6):S16-21. DOI:10.1016/j.jadohealth.2012.06.025^,2222. Dumith SC, Gigante DP, Domingues MR, Hallal PC, Menezes AMB, Kohl HW. Predictors of physical activity change during adolescence: a 3.5-year follow-up. Public Health Nutr. 2012;15(12):2237-45. DOI:10.1017/S1368980012000948 (Table 3).

Even if present in only three articles each, two other observations should be considered. The first is the positive associations between longer screen time and the consumption of foods rich in energy and fats (such as snacks, sweet biscuits, sausages and cold meats, and drinks of high energy density)⁷7. Camelo LV, Rodrigues JFC, Giatti L, Barreto SM. Lazer sedentário e consumo de alimentos entre adolescentes brasileiros: Pesquisa Nacional de Saúde do Escolar (PeNSE), 2009. Cad Saude Publica.2012;28(11):2155-62. DOI:10.1590/S0102-311X201200110001^,1414. de Moraes ACF, Adami F, Falcão MC. Understanding the correlates of adolescents’ dietary intake patterns: a multivariate analysis.Appetite. 2012;58(3):1057-62. DOI:10.1016/j.appet.2012.01.024^,3030. Fernandes RA, Christofaro DGD, Casonatto J, Kawaguti SS, Ronque ERV, Cardoso JR et al. Cross-sectional association between healthy and unhealthy food habits and leisure physical activity in adolescents. J Pediatr (Rio J). 2011;87(3):252-6. DOI:10.2223/JPED.2093. The other is the protective associations between living in inland towns or rural areas and sedentary behavior¹⁹19. Dias PJP, Domingos IP, Ferreira MG, Muraro AP, Sichieri R, Gonçalves-Silva RMV. Prevalence and factors associated with sedentary behavior in adolescents. Rev Saude Publica. 2014;48(2):266-274. DOI:10.1590/S0034-8910.2014048004635^,6464. Silva KS, Nahas MV, Peres KG, Lopes AS. Fatores associados à atividade física, comportamento sedentário e participação na Educação Física em estudantes do Ensino Médio em Santa Catarina, Brasil. Cad Saude Publica. 2009;25(10):2187-200. DOI:10.1590/S0102-311X2009001000010^,6969. Tenório MCM, Barros MVG, Tassitano RM, Bezerra J, Tenório JM, Hallal PC. Atividade física e comportamento sedentário em adolescentes estudantes do ensino médio. Rev Bras Epidemiol.2010;13(1):105-17. DOI:10.1590/S1415-790X2010000100010. On the other hand, due to the limited number of articles and similar distribution between the presence or absence of statistically positive associations, there still is uncertainty as to the possible associations between high levels of sedentary behavior and the variables “high socioeconomic status” (n = 9 articles), “age” (n = 7 articles) and “sex” (n = 3 articles) (Table 3).

DISCUSSION

The main results of this systematic review come from the data of 49 articles involving samples of Brazilian child and adolescent populations. In this set, we highlight the large number of cross-sectional studies, as well as the great methodological discrepancy among the articles as to the types of sedentary behaviors evaluated and the cut-off points used to characterize excess of time spent in sedentary behaviors. The analyzed articles showed greater consistency in the statistically positive associations between long exposure time to sedentary behavior and two variables: (i) high levels of body weight and (ii) low levels of physical activity.

On the methodological aspects, the present study identified the lack of standards in the assessment of sedentary behavior in children and adolescents, either for different ways to characterize these behaviors (e.g., screen time, time sitting down, television time) or for the methods and tools used in its assessment (international questionnaires, national questionnaires, or even questionnaires developed specially for those studies)⁹9. Clark BK, Sugiyama T, Healy GN, Salmon J, Dunstan DW, Owen N. Validity and reliability of measures of television viewing time and other non-occupational sedentary behaviour of adults: a review. Obes Rev. 2009;10(1):7-16. DOI:10.1111/j.1467-789X.2008.00508.x^,5151. Pearson N, Biddle SJ. Sedentary behavior and dietary intake in children, adolescents, and adults: a systematic review. Am J Prev Med. 2011;41(2):178-88. DOI:10.1016/j.amepre.2011.05.002. Since all the studies used questionnaires to measure sedentary behavior, one of the main challenges for future research is adding objective measurements in its methods (e.g., by motion sensors, such as ActiPal and accelerometers) to complement the self-reported data, controlling the memory bias, as observed in a study with adults³⁹39. Healy GN, Clark BK, Winkler EAH, Gardiner PA, Brown WJ, Matthews CE. Measurement of adults’ sedentary time in population-based studies.Am J Prev Med. 2011;41(2):216-27. DOI:10.1016/j.amepre.2011.05.005.

Twelve publications (24.5%) did not report any evidence of validation of the tool used. These findings reinforce the observation of Atkin et al.³3. Atkin AJ, Gorely T, Clemes SA, Yates T, Edwardson C, Brage S et al. Methods of measurement in epidemiology: sedentary behaviour. Int J Epidemiol. 2012;41(5):1460-71. DOI:10.1093/ije/dys118, who highlight the lack of good tools to assess sedentary behavior in epidemiological research. It is important that future studies, in addition to reporting the validation process of their questionnaires or presenting references that support such procedure, use validated questionnaires.

Corroborating the findings of a prior review⁷⁰70. Tremblay MS, LeBlanc AG, Kho ME, Saunders TJ, Larouche R, Colley RC et al. Systematic review of sedentary behaviour and health indicators in school-aged children and youth. Int J Behav Nutr Phys Act.2011;8:98. DOI:10.1186/1479-5868-8-98, most studies found characterize sedentary behavior as a measurement of television time or screen time, which combines the indicators of time spent watching television, using the computer and playing video games. However, these behaviors represent only part of the total time that children and adolescents spend in sedentary behavior throughout the day while they are awake. In addition, the studies included in this review showed high heterogeneity among the cut-off points adopted to define the excessive time of exposure to sedentary behavior. The cut-off point of two hours a day was the most frequent between the included studies, used in 16 articles. Even though Brazilian studies have not clarified the health risks of the amount of time spent in sedentary behaviors, a systematic review of international studies identified statistically significant associations between exposures of at least two hours and overweight, low physical fitness, low self-esteem and socialization, and low academic performance⁷⁰70. Tremblay MS, LeBlanc AG, Kho ME, Saunders TJ, Larouche R, Colley RC et al. Systematic review of sedentary behaviour and health indicators in school-aged children and youth. Int J Behav Nutr Phys Act.2011;8:98. DOI:10.1186/1479-5868-8-98.

About the regression models adopted, 22 articles (21 cross-sectional and one cohort study) used Poisson regression and 21 articles (19 cross-sectional and two case-control studies) used logistic regression. In six articles (four cross-sectional and two cohorts), analyses were performed using the linear regression model.

The positive associations observed between increased sedentary behavior time and increased levels of body weight corroborate the syntheses of reviews involving children and adolescents from different countries, regardless of their socioeconomic status⁴³43. Marshall SJ, Biddle SJ, Gorely T, Cameron N, Murdey I. Relationships between media use, body fatness and physical activity in children and youth: a meta-analysis. Int J Obes. 2004;28(10):1238-46. DOI:10.1038/sj.ijo.0802706^,4747. Mitchell JA, Byun W. Sedentary behavior and health outcomes in children and adolescents. Am J Lifestyle Med. 2014;8(3):173-99. DOI:10.1177/1559827613498700, and a synthesis of prospective studies conducted in high income countries such as Australia, Canada and the United States of America⁴⁸48. Must A, Tybor DJ. Physical activity and sedentary behavior: a review of longitudinal studies of weight and adiposity in youth. Int J Obes. 2005;29 Suppl 2:S84-96. DOI:10.1038/sj.ijo.0803064. As seen in this article, it is important to point out that this evidence is largely based on the results of articles assessing screen behaviors, with a particular focus on television time.

The positive associations observed between longer time in sedentary behavior and low levels of physical activity agree with a study conducted in high-income countries that showed negative relations between high screen time and moderate and vigorous physical activities⁴⁴44. Melkevik O, Torsheim T, Iannotti RJ, Wold B. Is spending time in screen-based sedentary behaviors associated with less physical activity: a cross national investigation. Int J Behav Nutr Phys Act. 2010;7:46. DOI:10.1186/1479-5868-7-46. The main recommendation of physical activity for health gains advocates moderate and vigorous intensity, disregarding light physical activities^aa World Health Organization. Global recommendations on physical activity for health. Geneva: World Health Organization; 2010.. Stronger inverse correlations have been found between sedentary behavior and light physical activities³⁹39. Healy GN, Clark BK, Winkler EAH, Gardiner PA, Brown WJ, Matthews CE. Measurement of adults’ sedentary time in population-based studies.Am J Prev Med. 2011;41(2):216-27. DOI:10.1016/j.amepre.2011.05.005. To avoid long uninterrupted periods of sedentary behavior, constant breaks are proposed during activities characterized as sedentary (< 1.5 MET), by inserting activities of higher energy expenditure³⁸38. Healy GN, Dunstan DW, Salmon J, Cerin E, Shaw JE, Zimmet PZ et al. Breaks in sedentary time - Beneficial associations with metabolic risk.Diabetes Care. 2008;31(4):661-6. DOI:10.2337/dc07-2046. Even though a recent meta-analysis pointed out the potential for this strategy with children and adolescents in the school environment³³33. Friedrich RR, Polet JP, Schuch I, Wagner MB. Efeito dos programas de intervenção no âmbito escolar para reduzir o tempo gasto em frente a telas: uma meta-análise. J Pediatr (Rio J).2014;90(3):232-41. DOI:10.1016/j.jped.2014.01.003, none of the interventions included were conducted in Brazil, which shows the need for these studies in the national research agenda.

Although observed in fewer publications, we found positive associations between more time spent in sedentary behavior and consumption of food and beverages of high energy content as well as positive associations between less time spent in sedentary behavior and living in inland towns or rural areas. In relation to the first result, this one’s data corroborate the findings of recent international studies that have shown associations between long screen time (≥ 20 hours per week) and high consumption of foods of high energy content (snacks, sweets and biscuits) and soft drinks⁶6. Berentzen NE, Smit HA, Rossem L, Gehring U, Kerkhof M, Postma DS et al. Screen time, adiposity and cardiometabolic markers: mediation by physical activity, not snacking, among 11-year-old children. Int J Obes.2014;38(10):1317-23. DOI:10.1038/ijo.2014.110^,3434. Garcia-Continente X, Pérez-Giménez A, Espelt A, Nebot Adell M. Factors associated with media use among adolescents: a multilevel approach.Eur J Public Health. 2014;24(1):5-10. DOI:10.1093/eurpub/ckt013^,4242. Mar Bibiloni M, Martínez E, Llull R, Pons A, Tur JA. Western and Mediterranean dietary patterns among Balearic Islands’ adolescents: socio-economic and lifestyle determinants. Public Health Nutr.2012;15(4):683-92. DOI:10.1017/S1368980011002199. Regarding the protective effect of living in inland towns or in rural areas, it is believed that children and adolescents who live in these places can have better opportunities for physical activity. The more favorable safety and traffic conditions would enable playing more freely in the communities and also using more bicycles¹⁹19. Dias PJP, Domingos IP, Ferreira MG, Muraro AP, Sichieri R, Gonçalves-Silva RMV. Prevalence and factors associated with sedentary behavior in adolescents. Rev Saude Publica. 2014;48(2):266-274. DOI:10.1590/S0034-8910.2014048004635^,6464. Silva KS, Nahas MV, Peres KG, Lopes AS. Fatores associados à atividade física, comportamento sedentário e participação na Educação Física em estudantes do Ensino Médio em Santa Catarina, Brasil. Cad Saude Publica. 2009;25(10):2187-200. DOI:10.1590/S0102-311X2009001000010. This would also reduce sedentary behaviors as screen activities in the leisure time and television watching for long periods. However, as the number of available national studies that assessed the occurrence of these associations is still small, more research is needed.

This systematic review showed some gaps among Brazilian studies about sedentary behavior such as the high number of cross-sectional studies included compared with the limited number of longitudinal studies⁵³53. Ramires V, Becker L, Sadovsky A, Zago A, Bielemann R, Guerra P. Evolução da pesquisa epidemiológica em atividade física e comportamento sedentário no Brasil: atualização de uma revisão sistemática. Rev Bras Ativ Fis Saude. 2014;19(5):529. DOI:10.12820/rbafs.v.19n5p529. As the cross-sectional study design does not establish antecedence between exposure and outcome variables, reverse causation can occur. This is the case of the main study finding: it is impossible to know the chronological sequence between sedentary behaviors and body weight and physical activity bevels in children and adolescents. In addition, the lack of longitudinal studies limits inferences about the dose-response relationships between sedentary behavior and the variables found. Another limitation was the high heterogeneity of the included articles in the forms of assessing sedentary behavior (screen, television, computer, seated, and total time), as the cut-off points adopted and the tools used for its evaluation.

The inclusion of all studies with repeated samples can be considered a potential limitation of this systematic review. This decision may have overestimated the results of comparison of the relationships between sedentary behavior and other outcomes or exposures, as high levels of body weight or low levels of physical activity. However, two methodological decisions led to the inclusion of these articles: the descriptive aim of the present review, which sought to provide an overview of the variables associated with sedentary behavior in children and adolescents, and the planning of not conducting a meta-analysis.

Based on the data identified in this review, we can make some conclusions. There are still few studies that measure sedentary behavior beyond screen time (television, computer, video games). New studies may involve measurement of time spent on cell phones and tablets, as well as in other domains, such as sitting down in transit or in the school environment. Another point is the need to use validated questionnaires in conjunction with objective tools to strengthen the information about the association between time spent in sedentary behavior and different outcomes. In view of the predominance of cross-sectional studies, longitudinal studies are needed, especially to establish the chronological sequence of events and the dose-response relationship. On the results available, the studies conducted with samples of Brazilian children and adolescents showed mainly associations between increased sedentary behavior and “high levels of body weight” and “low levels of physical activity” in different regions of Brazil.

REFERENCES

Publication Dates

History