We know that as a population in Ireland (and this is true of many Westernised developed countries) that we aren’t getting enough physical activity into our week. Just 32% of Irish adults are sufficiently active according to our national physical activity guidelines (Healthy Ireland, 2015), and this figure is even lower among children at primary and post-primary level. I’ve written on the topic of physical inactivity previously on my blog (find that article here) because it’s a public health issue I’m really passionate about. In this week’s Friday Focus, we’re going to look at movement from a different perspective however. You may have seen headlines in the past few months along the lines of ‘Sitting is the New Smoking‘, and wondered what THAT is all about. Although such headlines are a classic example of the conflation of science and evidence by mass media leading to public confusion, the issue of sedentary behaviour is one worth addressing and clarifying. I also recently spoke about this on my weekly iRadio interview, and thought I would bring it to my blog as well! So keep reading gang, as I dive into what sedentary behaviour is and it’s potentially negative effects on our health, and most importantly, the evidence to date for what we can do to offset these adverse effects. Whether you have to mostly sit at work, at school/university or at home, or even if you have a job that keeps you on your feet, this article has information for everyone, and is particularly relevant in our modern world that makes it easier to be sedentary getting from A to B than to be active! As always, my references in full are at the end of this article for those interested!
What is Sedentary Behaviour?
Sedentary time is the total amount of time (usually expressed per day) of sitting and lying down, excluding sleep time. Sedentary behaviour is the pattern of sedentary time; how it is dispersed over the day and is widely defined as any waking behaviour characterized by an energy expenditure ≤1.5 METs while in a sitting, reclining or lying posture.
Hang on Ciara – what is a ‘MET’?
Good question! Exercise experts measure activity in metabolic equivalents, or METs. One MET is defined as the energy it takes to sit quietly. So light physical activity, such as housework or strolling, uses less than 3 METs. Moderate-intensity activities are those that get you moving fast enough or strenuously enough to burn off three to six times as much energy per minute as you do when you are sitting quietly – exercises that are considered moderate intensity use anywhere from 3 to 6 METs, so a brisk walk is the classic example. Lastly, vigorous-intensity activities are those which burn more than 6 METs – examples include jogging, spinning or other high intensity training. A limitation of MET however is that it doesn’t take into account the level of fitness of a person – for example, an activity that makes me use 6 METs might not be the same for you – it could be lower or higher!
Okay, I get it – so back to sedentary behaviour.
Sedentary behaviour is not physical inactivity by a different name. The low energy requirement is what distinguishes sedentary behaviours from others that also occur whilst seated but may need greater effort and energy expenditure – for example, rowing or cycling. In many of our modern industrialised societies and environments, occupational (i.e. at work) sitting constitutes the major source of sedentary behaviour in adults, but it may also be accumulated whilst using motorised transport – this is particularly true for when we go from door to door, such as from home, to work, to home again. Lastly, it’s important to note that we talk about sedentary behaviour in terms of volume when we’re looking at it’s potential effect on our health – low volume being less than 4 hours per day and 8 or more hours per day being considered a high volume of this type of behaviour.
Okay, so if they’re not the same thing, then what’s the big difference between sedentary behaviour and physical inactivity?
Sedentary behaviour is not simply as a lack of physical activity, but is a separate behaviour in its own right – although sedentary behaviour and MVPA are part of the same energy expenditure spectrum. Most research studies these days use the term inactive to describe people who are performing insufficient amounts of moderate- and vigorous-intensity activity (MVPA), i.e. not meeting specified physical activity guidelines. For example – if I go for a 30-45 minute brisk walk 5 days a week, I’m meeting our national exercise guidelines, but I might also be very sedentary in my day job. Conversely, when I’m working at the hospital I’m on my feet all day i.e. not sedentary, but I might not do any exercise outside of work. It is possible for individuals to participate in the recommended amount of physical activity and also engage in high levels of sedentary behaviour, and importantly, the health outcomes associated with sedentary behaviour have often been identified independent of participation in physical activity. To give you an example at a national level, the 2015 Healthy Ireland survey found Irish adults spend on average 6 hours 36 minutes sitting on an average day, while just 32% were meeting physical activity guidelines – separate measurements but both independently and synergistically affect health.
Is sedentary behaviour harmful to our health?
Good question, because research suggests the volume of sedentary time increases with age – a US study in the American Journal of Public Health published last year reported the average for US adults to be 9 hours per day, and 10 hours per day in older adults. So we need to know whether it has potential negative implications for our short and/or long-term health, and what we can do about it throughout life. Its important to note here is that although the data on this topic is subject to ongoing research, there are many flaws to it and a lot of limitations to what we can conclude from it as a result. For example – a lot of factors influence sitting time – age, gender, occupation, socio-economic status, cultural factors, family norms, and accessibility (e.g. to TV, screens, leisure amenities and facilities), not all of which are measured by researchers, and in addition, how sitting time is measured, and the study design used, varies across studies conducted both within and between difference countries.
So what can we say at present? Well, a publication by the British Heart Foundation in 2012 reviewed the evidence to date at that time looking at sedentary behaviour and it’s effect on our health, and concluded that for adults, this type of behaviour is associated with an increased risk of type 2 diabetes, cardiovascular disease and death from all causes. It may also increase the risk of certain cancers but the findings from these studies were inconsistent. Interestingly, they also said that despite being widely studied, the association of sedentary behaviour with overweight/obesity or weight gain remains plausible yet unproven. In terms of mental health, there is a small amount of evidence to suggest adverse effects on our mental health (particular depression) and psychological well-being from sedentary behaviour too.
The British Heart Foundation also noted there is an overall lack of evidence looking at sedentary behaviour and health outcomes in children and young adults, although there is some evidence for associations with adverse cardiovascular risk profiles. Overall, much more and higher quality research needed, but there seems to be enough to say that high volumes of sedentary time, particularly going past 7-8 hours per day of sitting time, have detrimental effects on our health, particularly our cardio-metabolic health. BUT a lot of gaps in the literature remain, and right now it seems the catchy media headlines are racing far ahead of the scientific evidence. In addition, we definitely have a public health issue with levels of physical inactivity that are too low, and we definitely need to communicate accessible messages about breaking up sedentary/sitting time, but it’s a massive and inaccurate stretch to say ‘it’s the new smoking’, both from a health and economic perspective.
What can we as individuals do to offset these potential effects on our health?
Okay, so we definitely have some important take home positive points here, and I’ve saved them for last because they’re want I want to emphasise the most to you guys. A major study published by the Lancet in 2016 looked at lots of different studies examining individual physical activity levels and whether these attenuated or eliminated the association between sitting time and mortality from all causes. Over 1 million men and women were included in this study! For high sitting time (8 hours or more), the researchers found 60-75 minutes per day of moderate intensity physical activity (e.g. brisk walking) seemed to eliminate the increased mortality risk associated with this high volume. Of note, the most vulnerable group in this study was found to be those who had high volumes of sitting time AND high levels of physical inactivity, a combination we know is NOT good for our health in any way.
Now, given that that the volume of moderate intensity physical per week I’ve mentioned above which offset the detrimental effects of prolonged sitting is a LOT more than the 30 minutes, 5 days a week that our current national exercise guidelines advise. So I understand it can seem very daunting and understandably may not be achievable for many. However, what we can say is this:
- We should minimise prolonged bouts of sedentary time and behaviour – for example, try to break up each hour of sitting with a ten minute walk, or even five minutes (some is better than none!)
- If possible, fit bouts of moderate intensity activity into your day in a way that works and is feasible for you – for example, maybe consider active transport through cycling, getting off the bus a stop early, or try talking a walk in the morning and get up half an hour earlier, slotting in a lunch time walk as a daily habit, and/or now that the evenings are longer, try a short stroll after dinner!
- Remember our exercise guidelines – 150 minutes per week of moderate intensity physical activity (e.g. 30 minutes per day on 5 days a week, but you can split it up whatever way works for you!). Note that this is a MINIMUM recommended volume, and even the smallest amount of exercise does have health benefits. In addition, we’re advised to do at least 2 bouts of activities that promote muscle strength and balance per week.
- For children, an hour per day of activity is advised.
Adhering to these guidelines has wide-ranging benefits with a lot more evidence to support them than we currently do for sedentary behaviour, and these benefits are independent of minimising sedentary behaviour. In my opinion, we need to take a balanced approach to sitting time, as it can be beneficial for us to sit too – for example, to rest, sleep, engage in social activity and eat. A case of quality over quantity I think – remember, sit less, move more!
Lastly – is there evidence for workplace interventions to reduce sedentary behaviour?
A very interesting area, so I thought I’d read into it a little bit for you guys. The most recent Cochrane review of workplace interventions to reduce sitting time found after looking at 34 studies with a total of over 3000 subjects from developed countries that although standing desks are popular, their health benefits are uncertain. They do reduce total sitting time, and in this review weren’t found to have harmful effects (e.g. back pain, lower productivity, effects on veins), but the evidence overall was low quality according to the researchers. So more research needed on that! The authors also found inconclusive evidence on other interventions such as walking breaks and treadmill desks, but again the studies were of low quality and had low numbers of participants in them which limits conclusions. For the moment, let’s focus on what we’ve discussed in terms of guidelines for physical activity and reducing high and prolonged volumes of sedentary behaviour. Remember the take home point guys – sit less, move more!
And that’s a wrap! I really hope you enjoyed this week’s Friday Focus – as always, get in touch with any thoughts or comments! You know where to find me – @theirishbalance on Instagram/Twitter/Facebook!
Ciara 🙂 x
- Healthy Ireland 2015 – https://health.gov.ie/wp-content/uploads/2015/10/Healthy-Ireland-Survey-2015-Summary-of-Findings.pdf
- British Heart Foundation Sedentary Behaviour – https://www.getirelandactive.ie/Professionals/Health/Research/Children/BHF-Sedentary-Briefing.pdf
- Ekelund et al. (2016) – ‘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.’ The Lancet, 388(10051):1302-10.
- Vallance et al. (2018) – ‘Evaluating the Evidence on Sitting, Smoking, and Health: Is Sitting Really the New Smoking?’ American Journal of Public Health, 108(11).
- van der Ploeg and Hillsdon (2017) – ‘Is sedentary behaviour just physical inactivity by another name?’ International Journal of Behavioral Nutrition and Physical Activity, 14(142).