The health risks associated with prolonged sitting: a systematic review

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1 The health risks associated with prolonged sitting: a systematic review Name: Margaret Jane Anne Heaslop BSc (Hons), GradDip Sci Comm meg.heaslop@adelaide.edu.au Program: Master of Clinical Science Supervisors: Dr Christina Hagger BA (Hons), MBA, PhD Research fellow, Joanna Briggs Institute The University of Adelaide Professor Alan Pearson RN, ONC, DipNEd, MSc, PhD, FRNCA, FCN, FAAG, FRCN Executive Director, Joanna Briggs Institute Professor, Evidence-based Healthcare The University of Adelaide Associate Professor Neil King BSc, MSc, PhD (external supervisor) Director of Research, Institute of Health and Biomedical Innovation Queensland University of Technology Dr Edoardo Aromataris BSc (Hons) PhD (JBI contact person) Research Fellow, Joanna Briggs Institute The University of Adelaide

2 The health risks associated with prolonged sitting: a systematic review Review questions/objectives Review objective To critically appraise, synthesise and present the best available evidence concerning the cardiovascular and metabolic risks associated with prolonged sitting in otherwise healthy adults. That is, in adults who are not overweight, obese, or have any other existing metabolic or cardiovascular condition, does prolonged sitting increase the risk of obesity, diabetes, cardiovascular disease, stroke or other obesity-related health problems? Review question In healthy adults, does prolonged sitting increase the risk of obesity, diabetes, cardiovascular disease, stroke or other obesity-related health problems? Background Obesity and overweight are global health concerns in both the developed and developing world. 1 The World Health Organization predicts that 2.3 billion adults (approximately 33% of the world's population) will be overweight by The burden (in terms of morbidity and economy), for western countries, at least, is potentially huge, with obesity and overweight leading to near epidemic rates of cardiovascular disease, diabetes, musculoskeletal problems and some cancers. The causes of obesity and overweight namely, inadequate physical activity, overconsumption of kilojoules, or both (leading to an imbalance in energy expenditure) are well documented. 1 Consequently, public health initiatives have focused on promoting 'healthy eating' and physical activity through both dietary and physical activity guidelines and recommendations. Physical activity guidelines have traditionally recommended levels of physical activity that should be met for health benefits (that is, how much exercise to do). 2

3 Globally, these recommendations have differed in terms of amount, intensity, frequency and type of recommended activity; they have also evolved over time. 1-3 There is now growing recognition of the impact of sedentary behaviour on metabolic health. For many people in developed countries (and increasingly, in developing countries), workplaces are sedentary and a large proportion of waking hours are spent sitting down. 2 There is growing concern that these prolonged periods of sitting pose health risks, and that these risks are not counterbalanced by physical activity at other times. Prospective studies have found that sedentary activity, such as prolonged periods of sitting, is associated with obesity, metabolic syndrome and diabetes 3-5, and this association is independent of exercise. Of particular concern are the metabolic risks associated with too much sitting time at work 6, 7, irrespective of how much leisure time is spent in physical activity. Overall, it appears that total amount of sedentary time, and the way in which it is accrued, plays an important role in health outcomes. This review will look at the metabolic and cardiovascular risks associated with sedentary behaviours in particular, prolonged sitting time. Systematic reviews have been published on interventions, such as exercise, to reduce obesity. 7-9 A recent systematic review has looked at the health risks associated with occupational sitting. 10 This review included sitting time at work only (43 studies were included; studies that measured sitting in non-work times were excluded). Despite a comprehensive search strategy, the review did not report in detail (or analyse) specific results from the included studies; rather, results were reported in a narrative style. A more detailed systematic review of the risk factors associated with sedentary behaviour (eg prolonged sitting) at any time would therefore be useful and timely. The Australian Physical Activity Guidelines for Adults 11 recommend a minimum of 30 minutes physical activity on most days. These guidelines were based on the United States Centres for Disease Control and Prevention (CDC) and the American College of Sports Medicine (ACSM) physical activity recommendations, first published in In 2007, American physical activity guidelines for adults (eg the American Heart Association and the American College of Sports Medicine) were updated to increase the intensity of recommended activity, and now also stipulate the inclusion of vigorous-intensity exercise, as well as exercises to increase muscle strength and bone health. 13 The World Health Organization is also currently updating their guidelines for adults to reflect the growing 3

4 number of studies on physical activity and health. Despite these modifications, there is still no consensus on the recommended intensity or frequency of physical activity, or consistency in the way in which guidelines are presented at a regional and global level. 14 This problem is discussed in more detail in other reviews A summary of some key physical activity guidelines for adults across the world is provided in Appendix I. The guidelines all provide minimum recommended levels of physical activity. None yet recommend maximum amounts of physical inactivity, or recommend a reduction in the amount of physical inactivity. A preliminary search of the literature did not retrieve any randomised controlled trials; however, a growing number of prospective and other observational studies of adults are reporting preliminary results of the adverse effects of prolonged sitting. Several large prospective cohort studies have provided particularly useful data. 3,5,16-21 Some of these key studies are summarised below. An Australian cross-sectional study examined the association between television viewing time and continuous metabolic risk variables in healthy Australian adults who met Australian guidelines for physical activity measured as at least 2.5 hours of moderate to vigorousintensity self-reported physical activity per week. 3 Participants (2031 men, 2033 women; 25 years or older) had no diagnosed diabetes or heart disease. Outcomes were analysed separately for men and women, according to quartiles and hours per day of self-reported television-viewing time. After adjusting for confounders (age, education, income, smoking, diet quality, alcohol intake, parental history of diabetes, total physical activity time, menopausal status, use of postmenopausal hormones), there were significant dose response associations between television viewing time and: in men and women: waist circumference systolic blood pressure two-hour plasma glucose in women: fasting plasma glucose triglycerides high-density lipoprotein cholesterol. 4

5 These associations were stronger for women than for men. The authors concluded that the results supported the case for a concurrent sedentary behaviour and health guideline for adults, which is in addition to the public health guideline on physical activity. Several other cross-sectional studies have found an association between sedentary behaviour and obesity or obesity markers (eg waist circumference, glucose metabolism). 3,5,16-21 Prospective cohort studies have also reported an association between sitting time and metabolic risk factors in adults, independent of physical activity. Brown et al 17 found an association between self-reported sitting time and weight gain in Australian women; this association remained after adjusting for energy intake and physical activity in leisure time. A large prospective cohort study of women in the United States looked at sedentary behaviour (such as prolonged television-watching time) and the risk of obesity and type II diabetes in women. 22 The study excluded women who were already obese (ie had a body mass index >30), or who had diagnosed cardiovascular disease, diabetes or cancer. At sixyear follow-up, television-watching time was associated with an increased risk of obesity and type II diabetes; this association remained after adjusting for age, smoking, level of exercise and diet. Standing or walking was associated with a reduction in risk of obesity or diabetes. Inclusion criteria Types of participants This review will consider studies that include adults (approximately years; males and females), without existing metabolic or cardiovascular health problems (eg obesity, diabetes, cardiovascular disease, metabolic syndrome). Types of interventions/phenomena of interest The review will consider studies that evaluate sedentary behaviour, defined as prolonged sitting time, screen (television, computer) time, or any nonspecified sedentary behaviour (occupational or nonoccupational). For the purposes of the review, these key terms are defined as follows 10 : Sedentary behaviour: behaviours that have a low energy expenditure (eg >1.5 METs 6,10 [metabolic equivalent the ratio of the metabolic rate of an activity and the resting metabolic rate]). Sedentary behaviour does not include standing; rather, it can include: 5

6 prolonged sitting: sitting down for several hours at a time, without standing or walking breaks screen time: time spent sitting in front of a computer, television, video game, etc (either at work or in leisure time) nonspecified sedentary behaviour: any other behaviour that involves sitting or lying (eg driving, reading, listening to music, talking on the telephone). Types of outcome measures This review will consider studies that include the following primary outcome measures: incidence of obesity and obesity-related disease, including (but not limited to) type II (adultonset) diabetes, cardiovascular incidents (eg stroke, myocardial infarction), cardiovascular disease (eg heart failure), metabolic syndrome (according to the World Health Organization definition), all-cause mortality/morbidity. Secondary outcomes will include any cardiovascular or metabolic measures, such as insulin resistance or sensitivity, high blood pressure, body mass index (BMI), lean body mass/body composition (including change in adiposity, lean body mass, weight, etc), abdominal obesity (waist circumference), percentage body fat. Types of studies This review will include randomised controlled trials (RCTs), particularly if they report outcomes of interest in a control group. Due to the nature of the research question, however, RCTs may be rare prospective or other observational studies will be more likely. Therefore, in the absence of RCTs, study types will be included in the following order of preference: prospective cohort studies, all-or-none studies, retrospective cohort studies, case control studies, cross-sectional studies or case series. Search strategy The search will not be limited by date. Due to budget constraints, papers in languages other than English will be excluded, unless it is possible to translate them with the help of JBI staff members. Excluding papers published in languages other than English will be a limitation of the review. 6

7 The search strategy aims to find both published and unpublished studies. A three-step search strategy will be used in this review. An initial limited search of MEDLINE and CINAHL will be undertaken, followed by analysis of the text words contained in the title and abstract, and of the index terms used to describe articles. A second search using all identified keywords and index terms will then be undertaken across all included databases. Thirdly, the reference list of all identified reports and articles will be searched for additional studies. Key words will include those relating to the population and exposure (eg adult, sedentary lifestyle sedentary, sedentary behaviour, sitting, prolonged sitting, sitting time, sedentary time, television viewing, screen time, occupational sitting, physical inactivity), and outcomes (key words relating to obesity, cardiovascular disease, diabetes, stroke, etc). See Appendix IV for more details. The databases to be searched include MEDLINE, EMBASE, CINAHL, Cochrane Controlled Clinical Trials Registry (CENTRAL), PEDro, PsychINFO, SPORTDiscus and Web of Science. The search for unpublished studies will include the Australasian Digital Theses Program (ADT), Proquest, MEDNAR, the US National Institutes of Health international clinical trials registry ( and direct contact with principal investigators of relevant studies (where appropriate and possible). Assessment of methodological quality Quantitative papers selected for retrieval will be assessed by two independent reviewers for methodological validity before inclusion in the review, using standardised critical appraisal instruments from the Joanna Briggs Institute Meta Analysis of Statistics Assessment and Review Instrument (JBI-MAStARI) (see Appendix II). Any disagreements that arise between the reviewers will be resolved through discussion, or with a third reviewer. Data extraction Quantitative data will be extracted from papers included in the review using the standardised data extraction tool from JBI-MAStARI (see Appendix III). 7

8 The data extracted will include specific details about the interventions, populations, study methods and outcomes of significance to the review question and specific objectives. Data synthesis Quantitative papers will, where possible, be pooled in statistical meta-analysis using the Joanna Briggs Institute Meta Analysis of Statistics Assessment and Review Instrument (JBI- MAStARI). All results will be subject to double data entry. Where possible, results will be converted to a dichotomous format (eg presence/absence) and odds and risk ratios calculated using both fixed (within-study variation) and random effects models (to account for possible within and between-study variation) to explore potential heterogeneity. Heterogeneity will be assessed further using the standard Chi-square. Where different studies present data for a similar outcome but with adjustment for different factors, unadjusted values will be combined where possible. Considering the variety of study designs the review question predisposes itself to, any statistical analysis may be divided into subgroups on this basis if appropriate. Where statistical analysis is not possible, the findings will be presented in narrative form. Conflict of interest None to declare. Acknowledgments As this review will contribute towards the award of Master of Clinical, Science, a second reviewer will be used only for critical appraisal and data extraction. 8

9 References 1. Alberti, K.G. and P.Z. Zimmet, Definition, diagnosis and classification of diabetes mellitus and its complications. Part 1: diagnosis and classification of diabetes mellitus provisional report of a WHO consultation. Diabet Med, (7): p Anderson, L.M., et al., The effectiveness of worksite nutrition and physical activity interventions for controlling employee overweight and obesity: a systematic review. Am J Prev Med, (4): p Healy, G.N., et al., Television time and continuous metabolic risk in physically active adults. Med Sci Sports Exerc, (4): p Jans, M.P., K.I. Proper, and V.H. Hildebrandt, Sedentary behavior in Dutch workers: differences between occupations and business sectors. Am J Prev Med, (6): p Sugiyama, T., et al., Joint associations of multiple leisure-time sedentary behaviours and physical activity with obesity in Australian adults. Int J Behav Nutr Phys Act, : p Owen, N., A. Bauman, and W. Brown, Too much sitting: a novel and important predictor of chronic disease risk? Br J Sports Med, (2): p Shaw, K., et al., Exercise for overweight or obesity. Cochrane Database Syst Rev, 2006(4): p. CD Adegboye, A., Y. Linne, and P. Lourenco, Diet or exercise, or both, for weight reduction in women after childbirth. Cochrane Database of Systematic Reviews Art. No.: CD005627(3). 9. Curioni, C.C. and P.M. Lourenco, Long-term weight loss after diet and exercise: a systematic review. Int J Obes (Lond), (10): p van Uffelen, J.G., et al., Occupational sitting and health risks: a systematic review. Am J Prev Med, (4): p Australian Government Department of Health and Ageing, National Physical Activity Guidelines for Adults. Australian Government, Canberra, Pate, R., et al., Physical activity and public health: a recommendation from the Centres for Disease Control and Prevention and the American College of Sports Medicine. JAMA, : p Blair, S.N., M.J. LaMonte, and M.Z. Nichaman, The evolution of physical activity recommendations: how much is enough? Am J Clin Nutr, (5): p. 913S-920S. 14. Oja, P., et al., Physical activity recommendations for health: what should Europe do? BMC Public Health, : p Lankenau, B., A. Solari, and M. Pratt, International physical activity policy development: a commentary. Public Health Rep, (3): p Bertrais, S., et al., Sedentary behaviors, physical activity, and metabolic syndrome in middle-aged French subjects. Obes Res, (5): p Brown, W.J., et al., Identifying the energy gap: magnitude and determinants of 5-year weight gain in midage women. Obes Res, (8): p Dunstan, D.W., et al., Physical activity and television viewing in relation to risk of undiagnosed abnormal glucose metabolism in adults. Diabetes Care, (11): p Ford, E.S., et al., Sedentary behavior, physical activity, and concentrations of insulin among US adults. Metabolism, (9): p

10 20. Jakes, R.W., et al., Television viewing and low participation in vigorous recreation are independently associated with obesity and markers of cardiovascular disease risk: EPIC-Norfolk population-based study. Eur J Clin Nutr, (9): p Martinez-Gonzalez, M.A., et al., Physical inactivity, sedentary lifestyle and obesity in the European Union. Int J Obes Relat Metab Disord, (11): p Hu, F.B., et al., Television watching and other sedentary behaviors in relation to risk of obesity and type 2 diabetes mellitus in women. JAMA, (14): p

11 Appendix I Physical activity guidelines Table 1 Guideline Physical activity guideline recommendations for adults Recommendations Physical Activity Guidelines for Adults (Australian Government) The National Guidelines on Physical Activity for Ireland (Department of Health and Children) Physical Activity Guidelines for Americans (US Department of Health and Human Services) Canada's Physical Activity Guide to Healthy Living (Public Health Agency of Canada) Choosing Activity: A Physical Activity Action Plan (UK Department of Health) Global Recommendations on Physical Activity for Health (WHO) New Zealand Ministry of Health physical activity guidelines Minimum of 30 minutes of moderate-intensity physical activity on most, preferably all, days (this can be done all at once, or by combining bursts of minutes each over the day) Think of movement as an opportunity, not an inconvenience; be active in as many ways as you can; do regular, vigorous activity for extra health and fitness (this does not replace the other recommendations, but is an additional recommendation for those who are able, and wish, to achieve greater health and fitness benefits) At least 30 minutes of moderate activity a day, five days a week (or 150 minutes a week) (for all adults, years) 2 hours and 30 minutes per week of moderate-intensity, or 1 hour and 15 minutes (75 minutes) a week of vigorous-intensity aerobic physical activity, or an equivalent combination of moderate and vigorous-intensity aerobic physical activity Aerobic activity should be performed in episodes of at least 10 minutes, preferably spread throughout the week Additional health benefits are provided by increasing to 5 hours (300 minutes) a week of moderate-intensity aerobic physical activity, or 2 hours and 30 minutes a week of vigorous-intensity physical activity, or an equivalent combination of both Adults should also do muscle-strengthening activities that involve all major muscle groups performed on 2 or more days per week (all adults, years) Does not stipulate an amount, but encourages people to 'build physical activity into your daily life'; for example, moderate activity can consist of 30 minutes, 4 days a week The guidelines are currently being reviewed For general health benefit, adults should achieve a total of at least 30 minutes a day of at least moderate intensity physical activity on 5 or more days of the week At least 150 minutes of moderate-intensity aerobic physical activity per week or at least 75 minutes of vigorous-intensity aerobic physical activity throughout the week or an equivalent combination of moderate- and vigorous-intensity activity Aerobic activity should be performed in bouts of at least 10 minutes duration View movement as an opportunity, not an inconvenience Be active every day in as many ways as possible Put together at least 30 minutes of moderate intensity physical activity on most if not all days of the week If possible, add some vigorous exercise for extra health benefits and fitness 11

12 Exercise and Physical Activity Reference for Health Promotion 2006 (EPAR2006): Physical Activity, Exercise and Physical Fitness (Ministry of Health, Labour and Welfare of Japan, 2006) Either a daily walk of steps; or 35 minutes of jogging or tennis, or one hour of brisk walking, per week 12

13 Appendix II Critical appraisal instrument JBI Critical Appraisal Checklist for Comparable Cohort/ Case Control Reviewer Date Author Year Record Number Yes No Unclear 1. Is sample representative of patients in the population as a whole? 2. Are the patients at a similar point in the course of their condition/illness? 3. Has bias been minimised in relation to selection of cases and of controls? 4. Are confounding factors identified and strategies to deal with them stated? 5. Are outcomes assessed using objective criteria? 6. Was follow up carried out over a sufficient time period? 7. Were the outcomes of people who withdrew described and included in the analysis? 8. Were outcomes measured in a reliable way? 9. Was appropriate statistical analysis used? 13

14 Overall appraisal: Include Exclude Seek further info Comments (Including reason for exclusion) 14

15 JBI critical appraisal checklist for descriptive/case series Reviewer Date Author Year Record Number Yes No Unclear 1. Was study based on a random or pseudo- random sample? 2. Were the criteria for inclusion in the sample clearly defined? 3. Were confounding factors identified and strategies to deal with them stated? 4. Were outcomes assessed using objective criteria? 5. If comparisons are being made, was there sufficient descriptions of the groups? 6. Was follow up carried out over a sufficient time period? 7. Were the outcomes of people who withdrew described and included in the analysis? 8. Were outcomes measured in a reliable way? 9. Was appropriate statistical analysis used? Overall appraisal: Include Exclude Seek further info Comments (Including reason for exclusion) 15

16 JBI critical appraisal checklist for experimental studies Reviewer Date Author Year Record Number Yes No Unclear 1. Was the assignment to treatment groups truly random? 2. Were participants blinded to treatment allocation? 3. Was allocation to treatment groups concealed from the allocator? 4. Were the outcomes of people who withdrew described and included in the analysis? 5. Were those assessing outcomes blind to the treatment allocation? 6. Were the control and treatment groups comparable at entry? 7. Were groups treated identically other than for the named interventions? 8. Were outcomes measured in the same way for all groups? 9. Were outcomes measured in a reliable way? 10. Was appropriate statistical analysis used? Overall appraisal: Include Exclude Seek further info. Comments (Including reasons for exclusion) 16

17 Appendix III Data extraction form JBI data extraction form for experimental/observational studies Reviewer Date Author Year Journal Record Number Study Method RCT Quasi-RCT Longitudinal Retrospective Observational Other Participants Setting Population Sample size Intervention 1 Intervention 2 Intervention 3 Interventions Intervention 1 Intervention 2 Intervention 3 Clinical outcome measures Outcome Description Scale/measure Study results Dichotomous data 17

18 Outcome Description Intervention ( ) number / total number Intervention ( ) number / total number Continuous data Outcome Description Intervention ( ) number / total number Intervention ( ) number / total number Authors' conclusions Comments 18

19 Appendix IV Outline of search strategy Initial key words Population and exposure Outcomes adult, sedentary lifestyle sedentary, sedentary behaviour, sitting, prolonged sitting, sitting time, sedentary time, television viewing, screen time, occupational sitting, physical inactivity Obesity: obesity, weight gain, body mass index, adiposity, adipose, body size, skinfold thickness, abdominal fat, waist-hip ratio, hip circumference, arm circumference, fat, overweight Cardiovascular disease: cardiovascular, cardiovascular disease, vascular disease, myocardial infarction, heart attack, ischemia, ischaemia, coronary disease, atherosclerosis, arteriosclerosis, coronary risk factor, cardiovascular risk factor, hypertension, hyperlipidemia, hyperlipidaemia, cholesterol Diabetes: diabetes mellitus, type II, insulin resistance, metabolic syndrome, metabolic syndrome X, syndrome X, impaired glucose tolerance, noninsulin dependent, noninsulin treated, adult diabetes, maturity onset diabetes, NOT diabetes insipidus Stroke: stroke, carotid artery thrombosis, cerebrovascular accident, ischaemic attack, cerebral infarction, cerebral haemorrhage, subarachnoid haemorrhage General: morbidity, mortality, risk, longevity, life expectancy, illness, predictor, death, disease, health outcome Study design standard published search strings for RCTs and prospective studies 19