How does sitting all day affect my health?  Does exercise mitigate any damage?

The Quick Takeaway

  • People are sitting more, a trend exacerbated by the Covid 19 epidemic as people work from home, attend virtual meetings and shop on-line.
  • Sedentary behaviour, or too much sitting, is linked to many diseases and conditions including cardiovascular disease, type 2 diabetes and some cancers.
  • Sitting around eight hours a day puts an individual at risk.  Undertaking physical activity according to current guidelines is not on its own sufficient to overcome the adverse effects on health of too much sitting. 
  • Sedentary behaviour is a risk factor in its own right for poor health outcomes. It is a separate factor from not meeting the physical activity guidance.
  • To mitigate the adverse health effects of sitting for more than eight  hours a day, it may be necessary to do more than an hour of moderate to vigorous physical activity each day.
  • For the best health outcomes, people need to avoid for long periods and undertake physical activity.
  • Health can be protected by breaking up periods of sitting with light intensity physical activity, in other words, standing up and moving around.
  • We are beginning to understand why sedentary behaviour is bad for our health.   Prolonged sitting has been linked to an increase in the metabolic markers for cardiovascular disease, to alterations in glucose metabolism and increases in inflammatory markers.
  • There is a link between prolonged sedentary behaviour and being overweight.
  • Prolonged sitting seems to disrupt satiety such that long periods of sitting are associated with increased calorie intake.
  • National and international public health guidelines warn against the dangers of too much sitting.  No limit is given for the time spent sitting due to insuffeint research evidence.

The Full Deal

Introduction

Sitting, or being sedentary, has been increasing since the middle of the last century, and the Covid 19 epidemic led to further increases in sedentary behaviour as more people worked from home, participated in video conferences and did their shopping on line. People are often unaware of just how much time they spend sitting so perhaps a first step to becoming less sedentary would be to monitor the amount of time spent sitting (Bonnet and Barela, 2021). 

Sedentary behaviour has been linked to as many as 35 different diseases and disorders including premature mortality, type 2 diabetes, cardiovascular disease, cancer, overweight and obesity, sleep disorders, immune system dysfunction, and endocrine impairment (Bonnet and Barela, 2021).

People are at risk of the adverse effects of prolonged sitting even if they have other periods when they are physically active.  Eight hours sitting a day puts an individual at risk of poor health outcomes irrespective of whether they are physically active at other times, but the threshold could be as low as six or seven hours (Bonnet and Barela, 2021).  The adverse effects of prolonged sitting can be mitigated by breaking up the sitting periods by more dynamic activities such as squatting, kneeling, or sitting on a stool or ball (Bonnet and Barela, 2021)

The differences in health outcomes between sedentary and active behaviours have been recognised for some time. More than 70 years ago Morris and his team (Morris et al 1954; Morris and Raffle, 1954) conducted a series of studies with London bus workers.  They found that the bus drivers who had a sedentary occupation were at an increased risk of coronary heart disease compared to the bus conductors who had an active occupation collecting fares, walking around the bus and up and down the stairs of the double decker busses in use at that time.

Most waking hours are spent sitting

Adults typically spend 51-68% of their waking hours sedentary and only 5% of their waking hours undertaking vigorous physical activity (Dunstan et al, 2012).  The balance is spent on light intensity physical activity. The difference in activity can be expressed in terms of Metabolic Equivalents (METs) which compare the energy requirement for different activities to sitting still.  Sedentary behaviour uses 1-1.5 METs whereas a brisk walk uses 3 METs.  Things like TV viewing, using a computer or games console, workplace sitting and sitting in cars are all examples of sedentary behaviour.

Sitting is linked to adverse health outcomes

Many studies have demonstrated the dangers for health of prolonged sitting.  As always in health research meta-analyses and systematic reviews provide useful summaries of the evidence.  Chau et al. in 2013 reviewed six studies that investigated total daily sitting time and all-cause mortality. These six studies covered more than half a million individuals followed up for periods from 2.8 years to more than 8 years.  They found that each additional hour of sitting led to a 2% increase of all-cause mortality after correcting for physical activity. Individuals who sat the most had the worst outcomes.  Sitting for more than seven hours a day increased all-cause mortality by 5% for each hour of extra sitting.  The data showed that undertaking physical activity reduces the risks associated with prolonged sitting, especially for those that sat the most.

A larger meta-analysis by Biswas et al (2015) looked not only at all-cause mortality, but also at the relationship between sitting and cardiovascular disease, type 2 diabetes and cancer.  They found a correlation between sitting and all-cause mortality, cardiovascular disease mortality and cancer mortality as well as a correlation between sitting and cardiovascular disease incidence, cancer incidence and the incidence of type 2 diabetes. 

Ekelund et al (2016) combined data across 16 studies all examining sitting and all-cause mortality, as well as mortality from cardiovascular disease and from breast and colon cancer.  There were more than one million individuals in the data set and they were followed up for 2-18 years.  This study provided further evidence for the protective effect of physical activity.  There was no correlation between sitting time and all-cause mortality for the individuals that were the most physically active.  Individuals that sat for more than eight hours a day had to undertake 60-75 minutes of moderate to vigorous physical activity per day to negate the adverse effects on their health of sitting.  The results for cardiovascular disease mortality were similar to those for all-cause mortality, but the association between sitting and mortality from cancer was much weaker.  This study also looked at hours spent watching television (TV) as another measure of sedentary behaviour.  Watching TV for three hours per day or more was associated with increased mortality, except in the most active group where again the physical activity was protective.  This protection disappeared with five hours a day or more watching television. Overall, this data analysis showed that physical activity in line with current government guidance reduces the risk of mortality associated with sedentary behaviour but does not eliminate it.  Physical activity in excess of current government guidance is needed to eliminate the risk of prolonged sitting.

The data must be interpreted with caution

As always in this type of evidence review, it is important to understand how the data were collected to be confident of the relevance of the results.  Most of the studies included in the three large reviews discussed above are based on a single measure of sitting made only once at the start of the study.  It is then assumed that this behaviour is maintained during the follow-up period.  Studies in other related fields such as the relationship between physical activity and mortality and morbidity make similar assumptions, often relying on a single week’s pedometer reading at the start of the study.  Physical activity has been studied for longer than sedentary behaviour and there has been time to validate the findings with studies that include repeat measures of the amount of physical activity.  This has not been the case with the sedentary behaviour studies, but the large number of participants brings credibility to the results.  Another factor to consider in studies of this type is reverse causation meaning in this case that participants are sitting more because they are already suffering from chronic ill health. The investigators have, in most cases, taken into account reverse causation by eliminating from their analysis deaths that occur early in the follow up period.

Activity can mitigate the adverse effects of sedentary behaviour

A large study (Gao et al, 2024) published after the three major systematic reviews summarised above involved 481,688 healthy participants in Taiwan aged more than 20 who were divided into three groups.  Based on the participants’ occupation there was a group who were mostly sitting, a group that were mostly not sitting and a group that alternated between sitting and not sitting. The participants were followed up every two years for 12.85 years.  The results were adjusted for all the usual confounders of mortality data including sex, age, education, smoking, drinking and Body Mass Index (BMI).  The sitting group had a 16% higher risk of all-cause mortality and a 34% increase of cardiovascular disease mortality compared with the non-sitting group.  The alternate sitting and non-sitting group did not have a higher risk than the non-sitting group suggesting that the adverse health effects were due to prolonged sitting. Also in this study, high levels of leisure time physical activity appeared to mitigate the detrimental effects of long periods of sitting at work.

The importance of mitigating prolonged periods of sitting was investigated in another recent study.  Data were pooled (Sagelv et al, 2023) from participant cohorts from Norway, Sweden and the USA where accelerometer data was available to measure activity levels.  All participants were fifty years old or more.  There were 11,989 participants and they were followed up for 5.2 years.  The accelerometer data was used to divide participants into three activity levels, sedentary, light physical activity and moderate to vigorous physical activity.   For participants with less than 22 minutes of moderate to vigorous physical activity per day there was a curvilinear relationship between sedentary time and mortality.  For participants undertaking more than 22 minutes moderate to vigorous physical activity per day, sedentary time was not correlated with mortality. Light intensity physical activity was only associated with mortality risk in highly sedentary individuals.  The authors concluded that for the most sedentary individuals there are health benefits from light and moderate physical activity, but for those individuals that do not have sedentary lifestyles, moderate to vigorous physical activity is needed to achieve additional health benefits.

There are specific data showing that health outcomes are worse for long periods of uninterrupted sitting and that breaks in sitting are linked to better outcomes. Matthews et al (2012)[1] demonstrated in a large cohort of adults (240,819 aged 50–71), all healthy at the baseline assessment, that sedentary behaviour was linked to both all cause premature mortality and mortality from cardiovascular disease after correcting for potential confounders including age, smoking and diet.  They also found that the adverse effects of prolonged sitting, which was defined as sitting for more than seven hours a day, could not be fully mitigated by undertaking physical activity.  For healthy outcomes it is necessary to both undertake exercise and not sit for prolonged periods.

Get up and move around

It seems that it is necessary to undertake moderate to viperous physical activity to mitigate the effects of prolonged periods of sitting.  An alternative approach for a healthier behaviour may be to break up the periods of sedentary behaviour with periods of light physical activity. We saw earlier that sedentary behaviour is defined as 1.0-1.5 METS and the moderate to vigorous physical activity is greater than 3 METS.  Light intensity physical activity is in the range 1.6-2.9 METS and it is in this range where most daily energy expenditure occurs.  For most people, the alternative to sitting is light intensity physical activity.  Changing from sedentary behaviour to light intensity physical activity may be more realistic for many individuals (Dunstan et al 2012). Light intensity physical activity has been shown to have a beneficial effect on cardiac metabolic markers (Healey et al., 2007).  Interrupting sitting with light intensity physical activity has been shown to lead to improvements in post-prandial blood glucose and serum insulin, and to a suppression of lipoprotein activity, an enzyme which has a n adverse effect on lipoprotein uptake into muscle (Healey et al., 2007).

Carter et al. (2017) aimed to understand the relationship between sedentary behaviour and poor outcomes in terms of cardiovascular morbidity and mortality.  They found that prolonged sitting has an adverse effect on the markers of vascular health.  In their study they observed a downregulation of sheer rate and blood flow, alterations in glucose metabolism, alterations in inflammatory pathways and alterations in oxidative stress pathways.  They concluded that sedentary behaviour is a risk factor for cardiovascular disease in its own right and the observations are not simply due to the absence of physical activity.

Too much sitting and being overweight

It is clear that sedentary behaviour is an independent lifestyle factor influencing mortality and morbidity, having a direct impact that is not just a lack of undertaking the recommended amount of physical activity.  It is though linked with other factors that affect health outcomes. Sedentary behaviour is linked to increased body weight which is itself a known risk factor for poor health outcomes.  Observational studies have shown that overweight people spend more time sitting and that they sit for longer than people with healthy body weights (Bourdier et al, 2023).  This is an observation and does not demonstrate that being overweight causes people to sit more.  This type of observational study usually relies on self-reported measurements of sitting time rather than an objective measure such as accelerometer readings.  Overall people tend to underestimate the amount of time they spend sitting.   An alternative approach is a longitudinal study, where individuals are followed over time.  These studies have shown that prolonged sedentary behaviour, but not total sedentary behaviour is associated with a gain in BMI and waist circumference (Bourdier et al 2023).  These data too suggest that breaking periods of prolonged sitting with some sort of activity are beneficial for health.  

In their review, Bourdier et al (2023) found that reducing sedentary time and replacing it with low intensity physical activity can lead to weight loss and reduced adiposity and that moving throughout the day is important for maintaining weight loss.  The role of physical activity in achieving weight loss and maintaining a healthy weight is itself a disputed area (see “does exercise help with weight management” on this site) because there are compensatory behaviours that result in not all the energy expended in physical activity being directly related to weight loss.  Bourdier et al. (2023) argue that there may be less compensation in response to low level physical activity than there is to vigorous physical activity meaning that a replacement of sedentary behaviour with low level physical activity may be a good option for weight loss.  In making this statement the authors acknowledge that there is probably a lot of variation between individuals.

Bourdier et al.’s review (2023) also found evidence of sedentary behaviour having an influence on the control of food intake.  Long periods of watching TV are associated with an increase in the consumption of high calorie snacks.  Food cravings are more common during a day spent sitting than when there are regular breaks for activity.  The suggested explanation is that the body’s mechanism that matches food intake to activity is disrupted by periods of prolonged sitting.

Public health guidance

The relationship between sedentary behaviour and all-cause mortality is recognised in physical activity guidelines which recommend reducing the amount of sedentary time.  The UK Chief Medical Officers’ Physical Activity Guideline (Department of Health and Social Care, September 2019) specifically references the risks of sedentary behaviour for all cause mortality and cardiovascular disease mortality, and also cancer risk and survivorship.  The guidelines apply to all age groups, but do not state a time limit for sitting per day, due the guideline says, to lack of evidence.  The WHO Guidelines (2021) state that too much sedentary behaviour is bad for health and refers to increased risks of heart disease, cancer and type 2 diabetes.  The advice again is to limit sitting time, but without a specific limit.  The WHO emphasises the importance of reducing sedentary behaviour for all age groups and across the life course.

References

Biswas A, Oh PI, Faulkner GE, Bajaj RR, Silver MA, Mitchell MS, Alter DA. Sedentary time and its association with risk for disease incidence, mortality, and hospitalization in adults: a systematic review and meta-analysis. Ann Intern Med. 2015 Jan 20;162(2):123-32. doi: 10.7326/M14-1651. Erratum in: Ann Intern Med. 2015 Sep 1;163(5):400. doi: 10.7326/L15-5134. PMID: 25599350.

Bonnet C and Barela JA.  Health Issues Due to the Global Prevalence of Sedentariness and Recommendations towards Achieving a Healthier Behaviour.  Healthcare 2021, 9, 995.  https://doi.org/10.3390/healthcare9080995

Bourdier P, Simon C, Bessesen D, Blanc S,  Bergouignan A. The role of physical activity in the regulation of body weight: The overlooked contribution of light physical activity and sedentary behaviors. Obesity Reviews, 2023, 24 (2), pp.e13528. ￿10.1111/obr.13528.  hal-03856989￿

Carter S, Hartman Y, Holder S, Thijssen DH, Hopkins ND. Sedentary Behavior and Cardiovascular Disease Risk: Mediating Mechanisms. Exerc Sport Sci Rev. 2017 Apr;45(2):80-86. doi: 10.1249/JES.0000000000000106. PMID: 28118158.

Chau JY, Grunseit AC, Chey T, Stamatakis E, Brown WJ, et al. (2013) Daily Sitting Time and All-Cause Mortality: A Meta-Analysis. PLoS ONE 8(11): e80000. doi:10.1371/journal.pone.0080000

Department of Health and Social Care (2019) https://www.gov.uk/government/publications/physical-activity-guidelines-uk-chief-medical-officers-report

Dunstan DW, Howard B, Healy GN, Owen N. Too much sitting–a health hazard. Diabetes Res Clin Pract. 2012 Sep;97(3):368-76. doi: 10.1016/j.diabres.2012.05.020. Epub 2012 Jun 9. PMID: 22682948.

Ekelund U, Steene-Johannessen J, Brown WJ, Fagerland MW, Owen N, Powell KE, Bauman A, Lee IM; Lancet Physical Activity Series 2 Executive Committee; Lancet Sedentary Behaviour Working Group. Does physical activity attenuate, or even eliminate, the detrimental association of sitting time with mortality? A harmonised meta-analysis of data from more than 1 million men and women. Lancet. 2016 Sep 24;388(10051):1302-10. doi: 10.1016/S0140-6736(16)30370-1. Epub 2016 Jul 28. Erratum in: Lancet. 2016 Sep 24;388(10051):e6. doi: 10.1016/S0140-6736(16)31677-4. PMID: 27475271

Healy GN, Dunstan DW, Salmon J, Cerin E, Shaw JE, Zimmet PZ, Owen N. Objectively measured light-intensity physical activity is independently associated with 2-h plasma glucose. Diabetes Care. 2007 Jun;30(6):1384-9. doi: 10.2337/dc07-0114. Epub 2007 May 1. PMID: 17473059.

Gao W, Sanna M, Chen YH, Tsai MK, Wen CP. Occupational Sitting Time, Leisure Physical Activity, and All-Cause and Cardiovascular Disease Mortality. JAMA Netw Open. 2024 Jan 2;7(1):e2350680. doi: 10.1001/jamanetworkopen.2023.50680. Erratum in: JAMA Netw Open. 2024 Feb 5;7(2):e242037. doi: 10.1001/jamanetworkopen.2024.2037. PMID: 38241049; PMCID: PMC10799265.

Matthews CE, George SM, Moore SC, Bowles HR, Blair A, Park Y, Troiano RP, Hollenbeck A, Schatzkin A. Amount of time spent in sedentary behaviors and cause-specific mortality in US adults. Am J Clin Nutr. 2012 Feb;95(2):437-45. doi: 10.3945/ajcn.111.019620. Epub 2012 Jan 4. PMID: 22218159; PMCID: PMC3260070.

Morris JN, Heady JA, Raffle PAB, Roberts CG and Parks JW, (1953). Coronary heart disease and physical activity of work. The Lancet, 265(6975), 1053-1057.  doi:  10.1016/s0140-6736(53)90665-5

Morris J N and Raffle PAB (1954). Coronary Heart Disease in Transport Workers, A Progress Report. Brit. J. industr. Med., 11, 260

Sagelv EH, Hopstock LA, Morseth B, Hansen BH, Steene-Johannessen J, Johansson J, Nordström A, Saint-Maurice PF, Løvsletten O, Wilsgaard T, Ekelund U, Tarp J. Device-measured physical activity, sedentary time, and risk of all-cause mortality: an individual participant data analysis of four prospective cohort studies. Br J Sports Med. 2023 Nov;57(22):1457-1463. doi: 10.1136/bjsports-2022-106568. Epub 2023 Oct 24. PMID: 37875329.

WHO guidelines on physical activity and sedentary behaviour: at a glance. Geneva: World Health Organization; 2020. Licence: CC BY-NC-SA 3.0 IGO.

[1] This study is included in the data reviews of Chau et al 2013 and Ekelund et al 2016 referenced earlier in the text.