North Americans spend half their waking hours engaging in sedentary behaviour. Although several recent interventions suggest that short bouts of uninterrupted sedentary behaviour may result in acute increases in cardiometabolic risk, this literature has not been reviewed systematically. This study performed a systematic review of the impact of uninterrupted sedentary behaviour lasting ≤7 days on markers of cardiometabolic risk (insulin sensitivity, glucose tolerance, and fasting insulin, glucose, and lipid levels) in humans. Interventions were identified through systematic searches of Medline and Embase and screened by 2 independent reviewers. A total of 25 interventions were identified that examined the impact of imposed sedentary behaviour on biomarkers of interest. The majority of these studies focused on healthy young men, with very little identified research on females or other age groups. We found consistent, moderate quality evidence that uninterrupted sedentary behaviour ≤7 days results in moderate and deleterious changes in insulin sensitivity, glucose tolerance, and plasma triglyceride levels. In contrast, there is inconsistent, very low-quality evidence linking uninterrupted sedentary behaviour with changes in insulin, glucose, and HDL- and LDL-cholesterol levels. These findings suggest that uninterrupted bouts of sedentary behaviour should be avoided in order to prevent or attenuate transient increases in metabolic risk.
High levels of chronic sedentary behaviour are associated with increased risk of obesity [
In addition to the health impact of chronic sedentary behaviour, recent evidence suggests that increases in metabolic risk may be apparent following bouts of uninterrupted sedentary behaviour lasting just a few days in length [
Although several narrative reviews have discussed the acute changes in metabolic risk following short-term exposure to uninterrupted sedentary behaviour [
To be included in this paper, a study had to examine at least one of the following risk markers in humans: insulin sensitivity, glucose tolerance, or fasting insulin, glucose, or lipid levels. Uninterrupted sedentary behaviour had to be imposed by the researchers for a period lasting 7 days or less. Studies examining longer (e.g., chronic) bouts of sedentary behaviour were excluded as it was felt that it would be inappropriate to consider the impacts of both acute and chronic sedentary behaviour in a single systematic review, given the large amount of heterogeneity that this would introduce into the methodologies of included studies. Only intervention studies (both randomized and nonrandomized) that imposed on participants a controlled bout of sedentary behaviour were included in this paper.
For the purposes of this paper, sedentary behaviour was defined as a distinct class of waking behaviours characterized by little physical movement and low-energy expenditure (≤1.5 METs), as well as a sitting or reclining posture [
Literature searches were performed using Ovid Medline and Ovid Embase in March of 2012. The search strategy was created with the help of a research librarian and run by TJS (see Algorithm
(1) sedentar$.tw. (2) ((chair or sitting or car or automobile or auto or indoor or in-door or screen or computer) adj time).tw. (3) bed rest/ (4) weightlessness simulation/ (5) physical inactivit*.tw. (6) sedentary lifestyle/ (7) weightlessness/ (8) sitting/ (9) Suspension/ (10) Weight bearing/ (11) Head down tilt/ (12) posture/ (13) immobilization/ (14) or/(1)–(13) (15) cardiovascular fitness.tw. (16) metabolic syndrome x/ (17) Insulin Resistance/ or insulin/ (18) (metabolic cardiovascular syndrome or metabolic syndrome or syndrome x).tw. (19) exp cholesterol, hdl/ or exp lipoproteins, ldl/ or exp lipoproteins, vldl/ (20) Triglycerides/ (21) Glucose Intolerance/ or Glucose Clamp Technique/ or Glucose Tolerance Test/ or Blood Glucose/ (22) lipid metabolism/ (23) or/(15)–(22) (24) (14) and (23) (25) (24) not (animal/ not human/) (26) remove duplicates from (25)
Titles and abstracts of articles identified through the search were reviewed by two authors (T. J. Saunders and R. Larouche) using Reference Manager. Any articles identified as being potentially relevant by either reviewer were obtained for further screening. The full text of these articles was then reviewed independently by TJS and RL to determine whether the article met the
Data was extracted by T. J. Saunders and verified by R. Larouche. Information was extracted regarding study design (year, methodology, country, number of participants, duration of sedentary behaviour, age), modality of sedentary behaviour, risk factors examined, and main findings. Reviewers were not blinded to the authors or journals when extracting data. The primary summary measure was the mean difference in each outcome measure (or mean change in nonrandomized interventions) following exposure to acute sedentary behaviour. Where possible, effect sizes were calculated using Cohen’s
Following data extraction it became clear that the interventions included in the present paper were very heterogeneous in terms of the length of exposure, the type of sedentary behaviour that was examined, and even the measurement of individual risk factors (e.g., insulin sensitivity was assessed using HOMA, QUICKI, whole body insulin action, oral glucose tolerance tests, and hyperinsulinemic clamps). Thus, we believe that meta-analyses or pooling of data across studies would be inappropriate and have therefore performed a qualitative synthesis of the evidence instead.
Forest plots were created using Review Manager 5.1 (The Nordic Cochrane Centre, The Cochrane Collaboration) to display the relationship between sedentary behaviour and each outcome of interest. Studies assessing glucose tolerance and insulin sensitivity employed a wide range of methodologies and units of measurement, and plots for these outcomes are therefore presented as percent mean difference, while all other outcomes are presented as mean difference with 95% confidence interval. Studies which did not provide raw data were not included in forest plots.
The risk of bias and strength of evidence from individual studies was assessed using the Downs and Black Checklist [
The quality of evidence for each outcome was assessed as high, moderate, low, or very low using the GRADE approach [
After deduplication and the removal of conference abstracts the search strategy retrieved 5,670 articles for initial screening (Figure
Flow of articles through the search process.
A total of 29 articles reporting data from 25 independent interventions met all inclusion criteria and are presented in the current review. Nineteen of the identified interventions were nonrandomized trials, 4 were randomized crossover studies (e.g., participants served as their own controls), and 2 were randomized controlled trials. The studies included a total of 368 participants (309 males and 59 females), who were recruited from 12 countries across North America (USA), Europe (Denmark, France, Bulgaria, Russia, Greece, Sweden, Poland, and Slovakia, Norway), Asia (Japan), and Oceania (Australia). Participants ranged from 18 to 72 years of age, although the average age of participants was under 35 years for all but 3 studies, and under 30 for all but 7 studies. Sixteen studies employed head-up or horizontal bed rest, 5 employed head-down bed rest, 4 employed sitting, and one employed casting (one employed both sitting and head-down bed rest). The smallest studies had 5 participants [
Three studies examined the impact of 2, 4, and 5 hours of uninterrupted sedentary behaviour on biomarkers of interest, respectively; all other studies examined the impact of 1 day or more. Six studies examined the impact of 1 day of sedentary behaviour, 4 examined 2 days, 7 examined 3 days, 2 examined 4 days, 6 examined 5 days, 2 examined 6 days, and 8 examined the impact of 7 days of sedentary behaviour (6 studies collected data at multiple time-points). Characteristics of individual studies are presented in Table
Characteristics of included studies.
Reference | Design | First author | Year | Country | Age range | Mean age | Modality | Duration | Outcomes | Downs and Black | |
---|---|---|---|---|---|---|---|---|---|---|---|
[ | RCT | Yaroshenko | 1998 | Greece | 30 (30/0) | 22–26 | 24.8 | BR | 7 days | TG | 24 |
[ | RCT | Zorbas | 1999 | Bulgaria | 30 (30/0) | 22–26 | 24.3 | BR | 7 days | FG | 24 |
[ | RCO | Duran-Valdez | 2008 | USA | 10 (2/8) | 24–72 | 46.2 | BR | 2 days | FI, FG, IS | 21 |
[ | RCO | Stephens | 2010 | USA | 12 (6/6) | 19–32 | 26.1 | SIT | 1 day | FI, FG, IS | 24 |
[ | RCO | Dunstan | 2012 | Australia | 19 (11/8) | 45–65 | 53.8 | SIT | 5 hours | IS, GT | 27 |
[ | RCO | Nygaard | 2009 | Norway | 13 (0/13) | >50 | SIT | 2 hours | GT | 23 | |
[ | NT | Alibegovic | 2010 | Denmark | 38 (38/0) | 25.0 | BR | 7 days | FI | 23 | |
[ | NT | Alibegovic | 2009 | Denmark | 33 (33/0) | 25.6 | BR | 7 days | FI | 23 | |
[ | NT | Blanc | 2000 | France | 16 (8/8) | 30.2 | HDBR | 6 days | FI, FG, IS, GT | 23 | |
[ | NT | Dolkas | 1977 | USA | 7 (7/0) | 19–22 | 20.0 | BR | 4 days | FG | 21 |
[ | NT | Barbe | 1999 | France | 8 (8/0) | 23–31 | 27.1 | HDBR | 5 days | FI, FG | 21 |
[ | NT | Hamburg | 2007 | USA | 20 (14/6) | 30.7 | BR | 5 days | FI, FG, IS, TG | 23 | |
[ | NT | Katkov | 1979 | Russia | 5 (5/0) | 34.0 | BR | 5 days | FG | 17 | |
[ | NT | Kiilerich | 2011 | Denmark | 6 (6/0) | 22–36 | 28.7 | BR | 7 days | IS, GT | |
[ | NT | Ksinantova | 2002 | Slovakia | 15 (15/0) | 34.0 | HDBR | 4 days | FG | 20 | |
[ | NT | Lipman | 1972 | USA | 7 (7/0) | 18–20 | BR | 3 days | FI, IS, GT | 18 | |
[ | NT | Kanikowska | 2010 | Japan | 8 (8/0) | 27.0 | HDBR | 5 days | FI, FG, IS | ||
[ | NT | Mikines | 1989 | Denmark | 6 (6/0) | 25.0 | BR | 7 days | FI, FG, IS, GT | 20 | |
[ | NT | Moro | 2007 | France | 8 (8/0) | 22–27 | 23.0 | HDBR, SIT | 4 hours | FI, FG | 20 |
[ | NT | Navasiolava | 2010 | Russia | 8 (8/0) | 23.0 | BR | 7 days | FG, TG, HDL, LDL | 22 | |
[ | NT | Nygren | 1997 | Sweden | 6 (6/0) | 24.1 | BR | 1 day | FI, FG, IS | 22 | |
[ | NT | Richter | 1989 | Denmark | 5 (5/0) | 22–24 | CAST | 7 days | IS | 20 | |
[ | NT | Smorawinski | 1996 | Poland | 29 (29/0) | 20.10 | BR | 3 days | IS, GT | 19 | |
[ | NT | Stuart | 1988 | USA | 6 (6/0) | 21–28 | 23.0 | BR | 7 days | FI, FG, IS, GT | 22 |
[ | NT | Yanagibori | 1997 | Japan | 23 (13/10) | 19–25 | BR | 3 days | IS, GT, TG, HDL, LDL | 22 |
RCT: randomized controlled trial; RCO: randomized crossover; NT: nonrandomized trial; M: male; F: female; HDBR: head-down bed rest; 22BR: horizontal or head-up bed rest; SIT: sitting; CAST: casting; FG: fasting glucose; FI: fasting insulin; TG: triglycerides; HDL: HDL-cholesterol; LDL: LDL-cholesterol; IS: insulin sensitivity; GT: glucose tolerance.
When an intervention was described in more than one paper, the author name and year are taken from the earliest publication.
Two randomized crossover studies (
Forest plot of mean differences of fasting glucose and insulin values between sedentary behaviour and control conditions (sedentary behaviour-control).
Three nonrandomized interventions reported significant increases in insulin levels ranging from 26 to 47% following uninterrupted sedentary behaviour [
Given the aforementioned evidence from both randomized and nonrandomized interventions, we conclude that an acute bout of uninterrupted sedentary behaviour may result in a small-to-moderate increase in fasting insulin levels. However, the inconsistency of this effect and the lack of a statistical significance in randomized interventions leads us to conclude that the quality of this evidence is very low (Table
Summary of key evidence.
Risk factor | Number of studies | Number of participants (M/F) | Size of effect | Quality of evidence |
---|---|---|---|---|
Insulin sensitivity | 11 | 161 (118/43) | Moderate-to-Large | Moderate quality |
Triglycerides | 4 | 81 (65/16) | Moderate-to-Large | Moderate quality |
Glucose tolerance | 6 | 119 (83/36) | Moderate-to-Large | Moderate quality |
HDL-cholesterol | 3 | 51 (35/16) | Moderate | Very low quality |
Fasting insulin | 14 | 207 (187/20) | Small-to-Moderate | Very low quality |
Fasting glucose | 17 | 191 (163/28) | Small-to-Moderate | Very low quality |
LDL-cholesterol | 2 | 28 (22/6) | Moderate | Very low quality |
Two randomized crossover studies (
One nonrandomized intervention observed a significant increase in glucose levels of moderate size [
Given the evidence provided by 17 separate intervention studies, we conclude that an acute bout of uninterrupted sedentary behaviour may result in a small-to-moderate increase in fasting glucose levels. However, the high level of inconsistency from both randomized and nonrandomized interventions leads us to conclude that this evidence is of very low quality.
One randomized controlled trial (
Forest plot of mean differences of fasting lipid levels between sedentary behaviour and control conditions (sedentary behaviour-control).
The three nonrandomized interventions also found that acute sedentary behaviour resulted in significant increases in triglyceride levels [
Given the large and relatively consistent changes in triglyceride levels reported by both a randomized controlled trial and nonrandomized interventions, we conclude that acute bouts of uninterrupted sedentary behaviour result in a moderate-to-large increase in circulating triglyceride levels and that the available evidence is of moderate quality.
Three nonrandomized interventions (
Two nonrandomized interventions (
Three randomized crossover studies (
Forest plot of percent mean differences of insulin sensitivity and glucose tolerance between sedentary behaviour and control conditions (sedentary behaviour-control).
Two of the three randomized crossover studies [
Eight of the 10 nonrandomized trials reported significant reductions in insulin sensitivity ranging from 12.5% to 100% following uninterrupted sedentary behaviour. For example, Hamburg et al. [
Although the majority of studies (9/12) examining insulin sensitivity had no control group, the effect sizes of the sedentary behaviour interventions were consistently moderate to large. The results were also consistent, with 10 of 12 published studies reporting a reduction in insulin sensitivity in at least one subgroup of participants. Thus, we conclude that acute bouts of uninterrupted sedentary behaviour are likely to result in a moderate-to-large reduction in insulin sensitivity and that the available evidence is of moderate quality.
Two randomized crossover studies (
Both of the randomized crossover studies reported that uninterrupted sitting resulted in significant increases in glucose AUC in response to a standardized meal. Nygaard et al. reported that 2 hours of sitting resulted in a 45% increase in the glucose response to a standard meal in a group of 13 elderly women, in comparison to a combination of sitting and walking at a self-selected “very light” intensity [
Five of seven nonrandomized studies reported significant reductions in glucose tolerance in at least some participants, ranging from 7.8 to 30%. For example, Smorawiński et al. [
The available evidence suggests that acute bouts of uninterrupted sedentary behaviour may result in moderate-to-large reductions in oral glucose tolerance. Given the relatively consistent findings and the strong evidence from randomized crossover studies, we conclude that the evidence linking acute sedentary behaviour with reductions in glucose tolerance is of moderate quality.
Downs and Black scores assessing the risk of bias for individual studies are presented in Table
Based on our systematic review of data from 25 independent interventions, we found moderate quality evidence suggesting that acute bouts of uninterrupted sedentary behaviour lasting 2 hours to 7 days result in rapid and deleterious changes in triglyceride levels, insulin sensitivity, and glucose tolerance. We also found very low-quality evidence that it results in changes in fasting glucose, fasting insulin, and HDL- or LDL-cholesterol.
The findings of the current paper have important public health implications. Recent estimates suggest that on average North American adults and children spend 7–10 hours per day—more than half their waking hours—engaging in sedentary behaviour [
Research in animal models suggests mechanisms that may explain our observation of consistent changes in both insulin sensitivity and plasma triglyceride levels in response to uninterrupted sedentary behaviour. Bey and Hamilton reported that just 18 hours of hindlimb unloading results in near total cessation of lipoprotein lipase activity and roughly 75% reduction in triglyceride uptake in rat skeletal muscle [
The major strength of this paper is its rigorous systematic methodology. The search strategy was developed in consultation with a research librarian with expertise in search creation, and the screening process included two independent reviewers who came to consensus on all included studies. Strength of evidence was assessed using GRADE in order to increase the transparency of the grading process. Finally, the paper was prospectively registered with PROSPERO.
The limitations of this paper relate primarily to the quality of evidence that is presently available. Of 25 independent interventions identified by this paper, only 6 employed a randomized design. Further, although fasting glucose, glucose tolerance, insulin, and insulin sensitivity have each been examined by 9 or more investigations, lipid levels have received little attention by comparison. Given the small number of studies and the low quality of evidence currently available for these outcomes, it is difficult to determine their relationship with sedentary behaviour with any certainty.
There has also been a large amount of heterogeneity in the modality of sedentary behaviour (e.g., sitting versus bed rest) and in the way that outcome measures are calculated, which precluded the use of meta-analyses in the present paper. Only 5 studies identified by the current paper examined a modality of sedentary behaviour other than bed rest. The modality of sedentary behaviour which is most common in daily life is undoubtedly sitting, yet the acute impact of sitting has only been examined in four interventions. In contrast the metabolic impact of bed rest has received far more attention in the published literature [
The sample size of most interventions identified by this paper was quite small, and the vast majority of studies were performed in physically fit, healthy young adult males between the ages of 20 and 30. We only identified two interventions focused on individuals above the age of 50 [
It is also worth noting that, at present, it is difficult to differentiate the impact of sedentary behaviour
To date only three studies have examined the impact of uninterrupted sedentary behaviour lasting less than 1 day on markers of metabolic risk. Given that healthy individuals rarely spend 24 hours engaging in uninterrupted sedentary behaviour, it is important that future studies investigate whether shorter bouts of sedentary behaviour also have a measurable impact on metabolic health. Future work should also investigate the acute impact of sedentary behaviour on nontraditional markers of cardiometabolic risk including adipokines and markers of inflammation. Finally, none of the studies identified in the current paper examined whether these deleterious changes in risk markers persisted once participants returned to free living conditions. Thus, it is unclear whether the changes observed in the reviewed studies endure for several days following the cessation of sedentary behaviour, or whether they are rapidly resolved. Assessing the clinical significance of these changes will be difficult until their time-course has been more carefully examined.
This study demonstrates that, at present, there is moderate quality evidence that acute bouts of uninterrupted sedentary behaviour result in significant and deleterious changes in insulin sensitivity, glucose tolerance, and plasma triglyceride levels. There is currently very low-quality evidence linking uninterrupted sedentary behaviour with changes in circulating insulin, glucose, and HDL- and LDL-cholesterol levels. There is no evidence that acute bouts of uninterrupted sedentary behaviour provide any positive changes in markers of cardiometabolic risk. However, the majority of studies identified by this paper focused on healthy young men, and it is therefore unclear whether these results will generalize to females or to other age groups. These findings suggest that uninterrupted bouts of sedentary behaviour should be avoided in order to prevent transient increases in metabolic risk.
High-density lipoprotein cholesterol
Low-density lipoprotein cholesterol
Metabolic equivalent
Homeostasis model of assessment
Quantitative insulin sensitivity check index
Area-under-the-curve.
T. J. Saunders and R. Larouche are supported by Doctoral Research Awards from the Canadian Institutes of Health Research and Excellence Scholarships from the University of Ottawa. T. J. Saunders is also supported by a Doctoral Research Award from the Canadian Diabetes Association.
The authors report no conflict of interests.
T. J. Saunders, R. Larouche, R. C. Colley, and M. S. Tremblay developed the study rationale and criteria for inclusion and exclusion. T. J. Saunders developed and executed the literature search. T. J. Saunders and R. Larouche screened all potentially relevant articles. T. J. Saunders extracted data from included studies and wrote the first draft of the paper. R. Larouche checked data extraction, then reviewed, and edited the paper with R. C. Colley and M. S. Tremblay.
The authors are grateful to Margaret Sampson (Children’s Hospital of Eastern Ontario Research Institute) for her help in developing the search strategy and to their key informants for their help identifying relevant interventions.