BLOG BY Dr Ciara Kelly

Is Sitting Really The New Smoking?

Sit less, move more.’ Advice many of us have heard or read – on social media, tv and the radio, or perhaps from friends and family or a healthcare professional. You also may have seen headlines in recent months, boldly claiming  ‘Sitting is the new smoking!’ and wondered what the science really says on the topic.

By now, the majority of us are well aware of the wealth of benefits physical activity can bring to our physical and mental health. We know from years and years of research that both aerobic and resistance exercise are extremely important as part of a healthy lifestyle, and can improve our cardiovascular, metabolic, bone and mental health, to name but a few! National physical activity guidelines for adults in the U.K.1 advise us to undertake 150 minutes of moderate intensity physical activity per week (for example, 30 minutes per day on 5 days of the week, but it can split it up whatever way works for you!). Note that although this is the minimum recommended amount, even the smallest amount of exercise (yes, even just 10 minutes of a walk!) does have substantial health benefits. In addition, we’re advised to complete at least two bouts of activities that help keep our muscles, bones and joints strong each week (for example, resistance training using weights in the gym, doing yoga, or carrying heavy shopping). In 2016 in the UK, just 31% of men and 23% of women aged 16 and over met both the aerobic and resistance exercise guidelines2. Sub-optimal levels of physical activity are an issue worldwide - physical inactivity is in fact a leading risk factor for several chronic diseases3.

But what about sedentary behaviour and time spent sitting? Is that the same as physical inactivity? Actually, no! Sedentary behaviour is not simply a lack of physical activity but is a separate behaviour in its own right – although sedentary behaviour and physical activity are part of the same spectrum of energy expenditure. Sedentary time is the total amount of time (usually expressed per day) a person spends sitting and lying down, excluding sleep time. Sedentary behaviour is the pattern of sedentary time – i.e. how it is dispersed over the day, and can be defined as ‘any waking behaviour characterised by an energy expenditure ≤1.5 METs while in a sitting, reclining or lying posture’4. Exercise experts measure activity in metabolic equivalents, or METs. One MET is defined as the energy it takes to sit quietly, while a brisk walk might take anywhere from 3-6 METs5.

How sedentary behaviour is quantified varies in different studies, but most commonly, a low volume of sedentary behaviour is considered as being less than 4 hours per day and a high volume 8 hours or more per day. Approximately 29% of males and females in the UK spend an average of 6 or more hours of sedentary time on a typical weekday, with men being more likely to do so on weekend days2. In addition, the daily volume of sedentary time has been found to increase with age in the UK6. It’s important to note that it’s possible to be physically active but still have a large volume of sedentary behaviour, and vice versa.

Does this difference matter? Does sedentary behaviour carry health risks independent of how our physical activity levels? Well, that question is subject to ongoing research, but the evidence to date would suggest that it does to some extent. An evidence review on this question by the British Heart Foundation published in 20126 found that ‘Sedentary behaviour may be adversely associated with chronic disease in adults and risk factors for chronic disease in children and adolescents’. In particular, they found that there is consistent evidence that sedentary behaviour in adults is associated with an increased risk of type 2 diabetes mellitus, cardiovascular disease and death from all causes. More research was found to be needed as regards associations with increased risks of overweight and obesity, certain cancers and mental health. Now, of course, context is very important. For example, sitting down for an hour or two to catch up with a  friend is very different to two hours spent ploughing your way through a Netflix series. What seems to matter the most according to the research to date is the total volume of sedentary behaviour in the day and having frequent long periods of uninterrupted sedentary time.

Two further interesting questions on this topic addressed by a research group led by Ekelund et al. in 20167 were – could physical activity offset the potential health harms associated with a lot of sitting? And if so, then how much activity would be needed to do so? This group 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 (defined as 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 sitting. Of note, the group with the highest mortality risk in this study was found to be those who had high volumes of sitting time and high levels of physical inactivity. So this study tells us that being physically active can help offset the potential health risks of a lot of sitting (and even perhaps eliminate these risks for those who are very active). Plus, as mentioned, context matters in terms of what we do while we sit – for example, in this study, watching television for 3 or more hours per day was associated with an increased risk of death regardless of physical activity levels (except for the most active group).

So, is sitting the new smoking? We know far more about the significant health and economic burden that results from tobacco than we do about sedentary behaviour. Smoking directly affects the health of the smoker and indirectly affects the health of those in their environment due to the impact of second-hand smoke inhaled. However, as mentioned, sitting time and sedentary behaviour research to date tells us we should try to minimise prolonged bouts of sedentary behaviour and maximise our physical activity levels. To finish, here are some simple tips to help:

• Don’t forget our aerobic and resistance exercise guidelines as mentioned at the beginning of this article – start by finding enjoyable ways to move which you love to do and which help you meet these guidelines first and foremost.

• Try to break up prolonged periods of sitting with short breaks – for example, take even five or ten minutes to move and stretch for every hour of sitting.

• If possible, aim to fit bouts of moderate intensity activity (such as brisk walk, but lighter intensity movement counts too!) into your day in a way that works and is feasible for you. For example, perhaps consider active transport, getting off the bus a stop early, or try fitting short walks into your working day such as at lunch time!

• If you can, consider a standing desk at work – these can help reduce total sitting time in the day.

• Keep an eye on your screen time! Using smartphones, smart devices and television can lead to prolonged bouts of sitting time without us even realising it. This is especially important for children too! Consider setting time limits on use of these devices to help minimise the time spent sedentary while using them.

This blog post was written by Dr. Ciara Kelly (MB BCh BAO MRCPI MPH Sch), Irish-trained medical doctor specialising in public health medicine. She recently completed her Masters in Public Health and Nutrition in Ireland. She is the creator of The Irish Balance, a blog and social media platform focused on preventive medicine, health promotion and delicious recipes! You can find her @theirishbalance on Instagram, the blog at The Irish Balance and The Irish Balance Podcast.

References

1.Department of Health and Social Care (2019) ‘UK Chief Medical Officers’ Physical Activity Guidelines.’ Available at:  https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/829884/3-physical-activity-for-adults-and-older-adults.pdf

2.NHS Digital (2016) ‘Healthy survey for England 2016: Physical activity in adults.’ Available at: http://healthsurvey.hscic.gov.uk/media/63730/HSE16-Adult-phy-act.pdf

3.Guthold et al. (2016) ‘Worldwide trends in insufficient physical activity from 2001 to 2016: a pooled analysis of 358 population-based surveys with 1.9 million participants.’ The Lancet, 6(10):1077-1086. Available at: https://www.thelancet.com/action/showPdf?pii=S2214-109X%2818%2930357-7

4.Van der Ploeg and Hillsdon (2017) – ‘Is sedentary behaviour just physical inactivity by another name?’ International Journal of Behavioural Nutrition and Physical Activity, 14(142). Available at:  https://www.ncbi.nlm.nih.gov/m/pubmed/29058587/

5.Harvard T. Chan School of Public Health (2019) ‘Measuring physical activity.’ Available at: https://www.hsph.harvard.edu/nutritionsource/mets-activity-table/

6.British Heart Foundation (2012) ‘Sedentary behaviour.’ Available at: https://www.bhf.org.uk/informationsupport/publications/statistics/physical-inactivity-report-2017

7.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. Available at: https://www.ncbi.nlm.nih.gov/pubmed/27475271

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