- The UK population sit for 60-80% of the waking day during transport, work, education, care and leisure. This is equivalent to 8-10 hours per day and increases with age.
- Time spent sitting is the largest contributor to inactivity and forecasts estimate that this will increase at a rate of a quarter of an hour a day per year.
- Time spent sitting has two deleterious effects on health and well-being. It displaces physical activity and therefore prevents the population from reaping the health and well-being benefits of physical activity. However, increases in sedentary behaviour (SB) also have specific physiological effects that increase the risk of poor physical and mental health regardless of how physically active people are throughout the rest of the day.
- The evidence is robust enough that specific recommendations to limit sitting time at all ages were included in the UK physical activity guidelines. However, we lack evidence about how sitting time should be reduced and by how much to obtain net health benefit.
- The financial burden due to inactivity is currently estimated at £10 billion in England and is most likely to increase due to increased sitting time and the ageing of the population.
- Reducing sitting time has the potential to decrease the financial burden of inactivity, if sitting behaviour is targeted specifically. This targeting is important, as interventions to increase physical activity are ineffective in reducing the time the population spend sitting. Specific public health interventions and policies are required.
- Evidence shows that the impact of too much sitting and recommendations are poorly understood and known by the population and health practitioners.
- In order to develop specific public health interventions and policies, the factors that influence sitting need to be understood. Sitting is an intrinsic part of life in all sectors of society: in the transport, care and educational systems, at work and during leisure time. Currently, very little research has been devoted to understanding how personal, interpersonal, environmental factors influence sitting in these different contexts.
- If the level of inactivity in the UK population is to be improved, sedentary behaviours need to be specifically targeted. This requires the investment of resources into research to understand the impact of each societal sector on sitting time and how this can be sustainably changed.
Dr Sebastien Chastin. Senior Research Fellow, Institute of Applied Health Research, School of Health and Life Science Glasgow Caledonian University, Glasgow, UK.
On behalf of :
1) the Joint European Programme Initiative on healthy diet for healthy life, knowledge hub on Determinants of Diet and Physical Activity (DEDIPAC).
2) The MRC funded Seniors USP (Understanding Sedentary Patterns) Study
Dr Sebastien Chastin is the leader of DEDIPAC work on sedentary behaviour, work package lead within the MRC Seniors USP study, and the principle investigator of the International Classification of sedentary behaviour. His expertise is in behaviour dynamics (how and when people make choice to be active or not) and measurement of physical activity. He contributed as part of the Expert Working Group, to the UK physical activity guidelines “Start Active, Stay Active”.
Table of Contents
1.3 The “active couch potato” phenomena
2. Impact on health and well-being
3. Determinants of sitting (the 3 Ws)
5.3 Role of the health care system
Physical inactivity is recognised as one of three risk factors (along with poor diet and smoking) for all cause premature mortality, obesity, chronic diseases and disablement. Physical inactivity is now considered as a worldwide pandemic, a term used to characterise diseases that decimate populations [1]. In most developed countries, including the UK, less than one third of the population meet the recommended guidelines for physical activity [2]. The estimated health and economical cost of inactivity in the UK is £10 billion per year [3] . The largest contributor to inactivity is sedentary behaviour which is a cluster of behaviours that involve a seated or reclining posture and low energy expenditure, such as watching TV or driving a car. Sixty % of time spent inactive daily is spent sitting or in a reclining posture [4] with little energy expenditure, the equivalent to, on average, nine hours per day. The National Time Use Study report that time spent sitting has been increasing in the UK from around 30 hours per week in 1960 to around 45 hours per week in 2014 [5]. This trend is forecasted to continue at a rate of an additional quarter of an hour per year. In addition, these estimates and projections are based on self-reported data which underestimate the real time spent sitting by approximately 3 hours per day [6]. Therefore in 2014, it is more likely that the UK population spends around 66 hours per week sitting. The precise reasons for these trends are not known, but factors such as a shift in occupation towards desk and computer based jobs, increased use of screen based technology and a decline in active transportation are thought to play a major role [5].
While prolonged sitting time is prevalent in the whole population, there are trends for increasing sedentary behaviours with age [7]. Older adults are the most sedentary segment of society [8][9]. The ageing of the population and increased longevity are likely to lead to a further increase in sitting time. Similarly, there is trend for sitting time to be higher in men than women [5], [9]. The precise reason for this is not yet known, but it is hypothesised that it is due to different roles assumed in domestic tasks.
It is also worth noting that while an increase in sedentary behaviour is concomitant with a decrease in physical activity globally, the reverse is not necessarily true. Indeed, it is possible for an individual to engage in regular exercise and physical activity on a daily basis and meet the recommended guidelines for physical activity, but also spend the rest of the day sitting. This is known as the “active couch potato” phenomena [10].
Time spent sitting is associated with increased risk of premature death from all cause, increased risk of chronic disease (obesity, diabetes, osteoporosis, cardiovascular diseases), disablement, depression and loss of independence at all ages [10][19]. Individuals who age successfully, who maintain health, independence and quality of life in later life, tend to sit less [20]. The evidence in this respect is robust enough that specific recommendations to reduce prolonged sitting time at all ages were issued in the UK guidelines for physical activity [2].
The impact of increased sitting on health has double the impact of just not being active enough. Trends toward decreasing physical activity and increasing sedentary behaviour suggest that sitting tends to displace some physical activity, especially during leisure time and transportation [5]. While sitting or in a reclining posture, we are not active and expend very little energy. In other words, sedentary transportation and leisure denies the benefit of physical activity. It has been shown that displacing 30 minutes of physical activity with 30 minutes of sitting is associated with increases in biomarkers for obesity, diabetes, and cardiovascular diseases [21][22]. However, in the last 10 years, evidence has emerged showing that regardless of the level of physical activity, individuals who spend long periods of time sitting are at increased health risk [23]. This risk is not fully mediated by engagement in exercise or sports. Synthesis of the evidence at hand (through meta-analysis) shows that at equal physical activity levels, individuals who spend more sitting are at twice the risk of developing diabetes, twice the risk of premature death due to cardiovascular disease and 1.5 times the risk of premature death from all causes [16].
Currently, we do not understand precisely the mechanisms that makes too much sitting a health risk. It is likely to be a combination of physiological and social mechanisms. During sitting, our body responds differently to when we are standing [24][25]. Controlled laboratory experiments showed that prolonged sitting changes our physiology. For example, the way the body processes glucose is different whether we are standing, active or sitting [26]–[29]. There is evidence that prolonged sitting changes our physiology at the gene expression level [30]. These changes are small but it is thought that the cumulative effect through repeated and sustained exposure to sitting leads to a cumulative detrimental effect on our body. For example, bed rest studies, conducted mostly for space exploration research, have shown that prolonged immobility for several days lead to substantial loss of bone and muscle mass. Bed rest is not a likely scenario in everyday life, but more recently it was shown that repeated immobility during every day sitting is associated with poor bone and muscle health [19][31][32].
Aside from these direct physiological effects, it is also thought that sitting, especially time spent in front of the television and other screen based devises, might affect our health indirectly. Sitting time, especially in older adults and children, is strongly associated with social isolation and solitude which in turn are social determinants of health [33]. Finally, screen-based sitting time is thought to be associated with other unhealthy behaviours, such as snacking [34][35].
As part of the European Joint Initiative on the determinants of diet and physical activity (DEDIPAC)[36], a systematic synthesis of the evidence has been undertaken and concluded (reports will be available in 2015) that currently we have very little evidence on WHY the population sit so much, WHAT people do when sitting and WHERE they sit. Synthesis of expert opinions throughout Europe point toward a complex interaction between factors close to the individual (such as their psychology and physiology) and more distal factors (such as policy and cultural norms in several societal systems).
In the health care systems, for example, shift pattern, the organisation of care and potentially health and safety policy might contribute to keeping people sitting. In a recent study, it was shown that older adults who attended a geriatric rehabilitation ward spent the whole day sitting, aside from 30 minutes of physiotherapy [37]. They are discharged with improved functional capacity to walk and conduct tasks of daily living, but are also deconditioned and their behaviour altered towards increasing sitting. In part, this might be due to health and safety policy about risk of falls, staffing levels and lack of training, which encourages staff to maintain people in a seated or lying posture.
Similarly, active transport policy and working and educational cultures probably determine a lot of the time we spend sitting. However, there is currently no hard evidence to understand their effect or WHAT, WHEN and HOW they could be modified to change behaviour. Investment in specific research on the determinants of sedentary behaviour across the life course are required in order to inform public health policy and intervention to reduce sedentary time at all ages.
Currently, the majority of the evidence we have is based on self-reported data. Most population surveillance systems include questions about sitting time, but not in a systematic or interoperable way. International efforts are underway to harmonise measurement and data [36][38]. Nevertheless, self-reported data have low accuracy and tend to underestimate the size of the problem [6][39]. More objective means to collect this information exists [40] and needs to be adopted in public health and health care practice for accurate monitoring and evaluation of future interventions and policies.
The majority of our evidence is also based on cross-sectional studies, which limits our ability to draw conclusions about the determinants of sitting and its impact across the life course. Large longitudinal cohort studies are required at UK scale to understand the determinants of sitting. One such study, the MRC funded Seniors USP Study, hopes to answer some of these questions. Large multi-centred randomised controlled trials are required to establish the dose response relationship that will inform us about how much sitting time should be reduced by, or whether it is important to break up long periods of sitting even if we do not reduce total sitting time.
Few interventions to reduce sedentary time have been conducted to date, but these do indicate that it is feasible, it should be tailored to the context of that persons sedentary behaviour and that targeting the individual behaviour would only lead to small changes [41][42]. Qualitative data also indicates that changing or reducing sitting time might be perceived as easier than engaging in regular moderate physical activity [43].
Evidence shows that change in physical activity does not necessarily translate to changing sitting time [5] and interventions to increase physical activity do not change sitting behaviour [44]. Interventions need to specifically target sitting behaviour and be integrated within public health intervention to reduce inactivity. Simply spending money on sports facilities will not reduce the sitting problem.
Our lack of hard facts about the determinants of sitting is a major barrier to the development of effective and sustainable solutions to reduce sitting time. We also lack qualitative information on what people might agree to change, as sitting is an integral part of our life at home, work, school and during leisure. We need to understand when, where and how sitting can be changed in order to target the intervention. We also need to understand what could be consequences of changing practices (at school for example) and whether they would be adhered to.
Currently there is a real lack of knowledge within the health care system and within health care practitioners of the physical activity guidelines and specifically of the recommendation to reduce sitting time [45]. The NHS has a major primary and secondary preventive role to play. Some simple changes in practice could have major impact. A recent study showed that one year after discharge, stroke survivors spent as much time sitting at home as they did while in hospital just after their stroke [46], despite having recovered a large part of their functional capacity and ability to conduct tasks of daily living. This potentially puts these survivors at risks of secondary cardiovascular complication.
Physical inactivity is a major risk factor for health and wellbeing which cost the UK around £10 billion per annum and the majority of this burden is attributable to time spent sitting. Current activity guidelines recommend reducing sitting time at all ages. However, the current evidence base does not allow us to specify how to reduce sitting time and by how much to achieve net health benefit. Interventions and public health messages need to target sitting behaviour specifically and in addition to promotion of physical activity. Research investments are urgently required to provide the evidence base to achieve sustainable and effective change in sitting behaviour.
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