Research Review By Dr. Keshena Malik©


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Date Posted:

October 2015

Study Title:

Sedentary time & its association with risk for disease incidence, mortality, & hospitalization in adults


Biswas A, Oh PI, Faulkner GE et al.

Author's Affiliations:

Institute of Health Policy, Management and Evaluation, University of Toronto; University Health Network Toronto Rehabilitation Institute; Faculty of Kinesiology and Physical Education, University of Toronto; Department of Cardiology, Sunnybrook Health Sciences Centre; Osgoode Hall Law School, York University, Institute for Clinical Evaluative Sciences.

Publication Information:

Annals of Internal Medicine 2015; 162(2): 123–132.

Background Information:

Adults are advised to accumulate at least 150 minutes of weekly physical activity in bouts of 10 minutes or more (1). The intensity of habitual physical activity has been found to be a key characteristic of health prevention, with an established preventive role in cardiovascular disease, type II diabetes, obesity and some cancer types (2, 3). Despite the health-enhancing benefits of physical activity, this alone may not be enough to reduce the risk of disease and illness. Population-based studies have found that more than one half of an average person’s working day involves sedentary activities associated with prolonged sitting such as watching television or using the computer (4). Studies suggest that long periods of sitting have deleterious health effects independent of adults meeting physical activity guidelines (5-7).

The objective of this meta-analysis was to quantitatively evaluate the association between sedentary time and health outcomes independent of physical activity participation among adult populations. It was hypothesized that sedentary time would be independently associated with both cardiovascular and non-cardiovascular outcomes after adjusting for participation in physical activity. A further predication was that the relative hazards associated with sedentary times would be attenuated in those who participate in higher levels of physical activity compared to lower levels (8).

Pertinent Results:

Literature Search Results:
A total of 20,980 studies were identified through database searching and 25 studies were added after hand-searching in-text citations. No study was excluded solely because of low-quality scores less than 98 (< 50%). No randomized controlled trial met the selection criteria. Most studies used prospective cohort study designs and 3 studies used cross-sectional and case-control study designs. Definitions of sedentary time varied across studies.

Publication Bias & Heterogeneity:
There was statistical evidence of publication bias among studies reporting all-cause mortality (Egger regression intercept (ERI) 2.63 (p = 0.015)) and cancer incidence (ERI 1.87 (p = 0.046)). No statistical evidence of publication bias was found for cardiovascular disease mortality and cancer mortality (ERI 1.51 (p = 0.16) and 0.96 (p = 0.15), respectively). Publication bias was not assessed for cardiovascular disease incidence and type II diabetes incidence because the small number of studies may overestimate the effects of bias.

Heterogeneity across studies reporting all-cause mortality and cardiovascular disease incidence as outcomes may be high. Heterogeneity was low for cardiovascular disease mortality, cancer mortality, cancer incidence and type II diabetes incidence.

Association of Sedentary Time & Health Outcomes:
Greater sedentary time was found to be positively associated with an increased risk of all-cause mortality, cardiovascular disease mortality, cancer mortality, cardiovascular disease incidence, cancer incidence and type II diabetes incidence. The largest statistical effect was associated with the risk for type II diabetes (pooled hazard ratio (HR) 1.91 (CI 1.64-2.22)). Among studies assessing cancer mortality and incidence, significant associations were found for breast, colon, colorectal, endometrial, and epithelial ovarian cancer. One study evaluated whether sedentary behaviour was correlated with potentially modifiable hospitalization, revealing that self-reporting fewer than 8 hours of sitting time per day resulted in a 14% lower risk of potentially preventable hospitalization (HR 0.86 (CI 0.83-0.89)) (15).

Ten studies reported the effects of prolonged bouts of sedentary time modified by the highest or lowest reported participation in physical activity and health outcomes. The relative hazards associated with sedentary time on outcomes varied according to physical activity levels and were generally more pronounced at lower levels than at higher levels. Sedentary time was associated with a 30% lower relative risk for all-cause mortality among those with high levels of physical activity (pooled HR 1.16 (CI 0.84-1.59)) as compared with low levels of physical activity (pooled HR 1.46 (CI 1.22-1.75)).

Clinical Application & Conclusions:

This study demonstrated that sedentary time was independently associated with a greater risk for all-cause mortality, cardiovascular disease incidence or mortality, cancer incidence or mortality and type II diabetes in adults. The deleterious outcomes associated with sedentary time generally decreased in magnitude among persons who participated in higher physical activity compared to lower levels.

In other words, prolonged sedentary time, independent of physical activity, is positively associated with various deleterious health outcomes. The results reaffirm the need for greater public awareness about the hazards associated with sedentary behaviours. The results also justify the necessity for further research to explore the effectiveness of interventions designed to target sedentary time independently, and in addition, to those targeting physical activity.

The most important take home message for your practice = GET YOUR PATIENTS MOVING!!

Study Methods:

Data Sources and Searches:
  • The Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines were used in conducting and reporting this meta-analysis (9). Published studies on the association between sedentary behaviour and various health outcomes were identified and cross-checked by 2 reviewers through a systematic search of Medline, PubMed, EMBASE, CINAHL, Cochrane Library, Web of Knowledge and Google Scholar databases.
  • Health outcomes included all-cause mortality, cardiovascular disease incidence (including diabetes), cardiovascular disease mortality, cancer incidence, cancer mortality, and all-cause hospitalizations.
  • Searches were restricted to English-language primary research articles through August 2014 with no publication date limitations.
  • The following keywords were applied to the search: (exercise OR physical activity OR habitual physical activity) AND sedentar* OR inactivity OR television OR sitting) AND (survival OR morbidity OR mortality OR disease OR hospital* OR utilization).
  • References from relevant publications and review articles were hand-searched to supplement electronic searches.
Study Selection:

Inclusion Criteria:
  • Primary research studies assessing sedentary behaviour in adult participants as a predictor variable, independent of physical activity and correlated with at least one health outcome.
  • Sedentary behaviour defined as waking behaviours characterized by little physical movement and low-energy expenditure (≤ 1.5 metabolic equivalents) including sitting, television watching and reclined posture (10).
  • Studies that assessed the effects of varying intensities of physical activity that correlated with a measure of sedentary behaviour with an outcome.
Studies were excluded if they:
  • studied non-adult populations,
  • did not adjust for physical activity in their statistical regression models,
  • assessed only sedentary behaviour as a reference category to the effects of physical activity, or
  • measured sedentary behaviour as the lowest category of daily or weekly physical activity.
Data Extraction and Quality Assessment:

Data were extracted from articles that met selection criteria and were deemed appropriate for detailed review by 3 authors. The authors restricted studies reporting health outcomes to those with direct associations with death, disease incidence and health service use outcomes.

Individual study details were characterized by the following:
  • authors or year of publication
  • study design
  • sample size or characteristics (age and sex)
  • data collection methods
  • study outcomes
  • study limitations
  • hazard ratios odds ratios or relative risk ratios
Quality assessment of the articles was based on methods which have shown both face and content validity for limiting the risk of bias from study participation, study attrition, measurement of prognostic factors, measurement of (and controlling for) confounding variables, measurement of outcomes and analysis approaches (11-13).

Each study was evaluated according to a standardized set of predefined criteria consisting of 15 items (14). The authors required positive quality criteria of 8 items or more to be included in this study:
  1. Adequate description of source population
  2. Adequate description of the sampling frame, recruitment methods, period of recruitment and place of recruitment
  3. Participation rate at baseline ≥ 80% or if the non-response was not selective
  4. Adequate description of the baseline study sample for key characteristics (age, sex, sedentary behaviour, health outcome)
  5. Provision of the exact number at each follow-up measurement
  6. Provision of the exact information on follow-up duration
  7. Response at short-term follow-up (≤ 12 months) was ≥ 80% of the number of baseline, and response at long-term follow-up was ≥ 70% of the number at baseline
  8. Information on non-selective non-response during the follow-up measurement
  9. Adequate measurement of sedentary behaviour i.e., done my objective measures and not by self-report
  10. Sedentary behaviour was assessed at a time before the measurement of the health outcome
  11. Adequate measurement of the health outcome i.e., objective measurement of the health outcome done by trained personnel by means of a standardized protocol of acceptable quality and not by self-report
  12. The statistical model was appropriate
  13. The number of cases was ≥ 10 times the number of independent variables
  14. Presentation of point estimates and measure of variability (confidence intervals and standard error)
  15. No selective reporting of results

Study Strengths / Weaknesses:

  • This meta-analysis focused exclusively on studies that adjusted for physical activity.
  • This study provides greater insight into the various sources of heterogeneity compared to other systematic reviews published to date.
  • The authors contacted individual authors to confirm statistical effects.
  • This study only included English-language studies which could create a language or cultural bias.
  • The presence of publication bias with the possibility of selective reporting undermines the generalizability of this study’s findings.
  • The confidence intervals overlapped in the examination of whether prolonged bouts of sedentary time were modified by the highest or lowest reported participation in physical activity. Further studies will be required to confirm and better quantify how associations between sedentary time and outcomes attenuate at higher physical activity levels.
  • The study is limited in its conclusions by the heterogeneity across study methods for assessing sedentary behaviour, the key exposure variable (16).
  • Recommendations and/or guidelines on specific amounts of physical activity or sedentary time remain broad and non-specific due to the variation in sedentary behaviour measures and modest validity of the measures (17).
  • Perhaps the use of objective activity monitoring such as inclinometers/accelerometers can be used in future studies rather than self-report to minimize measurement error (16).

Additional References:

  1. Canadian Society for Exercise Physiology. Canadian Physical Activity Guidelines and Canadian Sedentary Behaviour Guidelines. 2013
  2. Warburton DER, Katzmarzyk PT, Rhodes RE et al. Evidence-informed physical activity guidelines for Canadian adults. Appl Physiol Nutr Metab 2007; 32: S16-S68.
  3. Lee IM, Sesso HD, Oguma Y et al. Relative intensity of physical activity and risk of coronary heart disease. Circulation 2003; 107: 1110-6.
  4. Matthews CE, Chen KY, Freedson PS, et al. Amount of time spent in sedentary behaviors in the United States, 2003–2004. Am J Epidemiol 2008; 167: 875-81.
  5. Dunstan DW, Salmon J, Owen N, et al; AusDiab Steering Committee. Associations of TV viewing and physical activity with the metabolic syndrome in Australian adults. Diabetologia 2005; 48: 2254-61.
  6. Hu FB, Leitzmann MF, Stampfer MJ, et al. Physical activity and television watching in relation to risk for type 2 diabetes mellitus in men. Arch Intern Med 2001; 161: 1542-8.
  7. Hamilton MT, Hamilton DG, Zderic TW. Role of low energy expenditure and sitting in obesity, metabolic syndrome, type 2 diabetes, and cardiovascular disease. Diabetes 2007; 56: 2655-67.
  8. Salmon J, Bauman A, Crawford D, et al. The association between television viewing and overweight among Australian adults participating in varying levels of leisure-time physical activity. Int J Obes Relat Metab Disord 2000; 24: 600-6.
  9. Moher D, Liberati A, Tetzlaff J, et al.; PRISMA Group. Preferred reporting items for systematic reviews and meta-analyses: the PRISMA statement. Ann Intern Med 2009; 151: 264-9, W64.
  10. Tremblay MS, Colley RC, Saunders TJ, et al. Physiological and health implications of a sedentary lifestyle. Appl Physiol Nutr Metab 2010; 35: 725-40.
  11. Proper KI, Singh AS, van Mechelen W et al. Sedentary behaviors and health outcomes among adults: a systematic review of prospective studies. Am J Prev Med 2011; 40: 174-82.
  12. Hoogendoorn WE, van Poppel MN, Bongers PM, et al. Systematic review of psychosocial factors at work and private life as risk factors for back pain. Spine 2000; 25: 2114-25.
  13. Singh AS, Mulder C, Twisk JW, et al. Tracking of childhood overweight into adulthood: a systematic review of the literature. Obes Rev 2008; 9: 474-88.
  14. Hayden JA, Cote P, Bombardier C. Evaluation of the quality of prognosis studies in systematic reviews. Ann Intern Med 2006; 144: 427-37.
  15. Tran B, Falster MO, Douglas K et al. Health behaviours and potentially preventable hospitalisation: a prospective study of older Australian adults. PLoS One 2014; 9: e93111.
  16. Lynch BM & Owen N. Too much sitting and chronic disease risk: Steps to move the science forward. Ann Int Med 2015; 162: 146-147 (Editorial).
  17. Clark BK, Sugiyama T, Healy GN, et al. Validity and reliability of measures of television viewing time and other non-occupational sedentary behaviour of adults: A review. Obes Rev 2009; 10: 7-16.