Sitting for just a couple hours has measurable (and negative) health impact

Last week a fascinating study was published by SBRN member David Dunstan and colleagues in Australia, which examined the acute (e.g. short-term) impact of uninterrupted sitting on metabolic health.  In this new study, individuals with overweight or obesity were asked to perform 3 separate conditions in random order.

  1. Uninterrupted sitting – participants sat for 5 consecutive hours
  2. Sitting plus light intensity breaks – similar to the uninterrupted sitting condition, except that participants had a 2 minute walk break at a light intensity every 20 minutes throughout the day
  3. Sitting plus moderate intensity breaks – similar to the light intensity breaks condition, except that the breaks were at a moderate intensity

The figure below nicely demonstrates the basic protocol for the three conditions.

Dunstan et al 2012 (Diabetes Care)

In all three conditions participants were given a standardized 760 calorie test drink at baseline (for reference, that’s about the same as a medium McDonald’s triple-thick milkshake), and had blood taken every hour to determine the glucose and insulin response.  This is pretty similar to an oral glucose tolerance test, except that the test drink included both sugar and fat, while an oral glucose tolerance test involves only sugar.  This sort of drink will produce a spike in insulin and glucose levels in the blood, but a healthier person will have a lower spike than an unhealthy person.  A big spike in glucose or insulin levels suggests that your body has to work harder to get sugar into your muscles, which is a sign of insulin resistance and a risk factor for diabetes.

So what happened?

Plasma insulin and glucose levels were higher on the day of uninterrupted sitting, in comparison to the days with light or moderate intensity breaks.  And not just a bit higher – more than 20% higher!  I’ve graphed the average insulin and glucose levels during each condition below.

Glucose response (Dunstan et al 2012)

Insulin response (Dunstan et al 2012)

Even more fascinating is that the groups seem to diverge almost immediately – in the figure below, you can see that the glycemic response to the test meal during the uninterrupted sitting seems to be distinctly higher than the other two conditions even just 1 or 2 hours into the session.

Glucose area-under-the curve (Dunstan et al 2012)

While that may seem surprising, another recent study published in Applied Physiology, Nutrition and Metabolism found that sitting for 2 straight hours (e.g. 120 consecutive minutes) following a standardized meal increased the glycemic response by >45%, in comparison to a combination of 40 minutes of very light intensity walking and 80 minutes of sitting.  In other words, these people had a clinically significant increase in metabolic risk simply because of an extra 40 minutes of sitting following the test meal.

What does this mean?

Taken together, these studies strongly suggest that sitting for several consecutive hours has a measurable and negative impact on metabolic health (at least in individuals with overweight or obesity).  This could go a long way to explaining the relationship between sedentary behaviour and mortality – if you are engaging in uninterrupted sitting for periods of a couple hours on a regular basis, that could be exposing your body to elevated glucose and insulin levels following every meal, which over the long term could have serious consequences.

On the bright side, these studies also suggest that simply taking an occasional walk break at a very light intensity could substantially reduce the impact of prolonged sitting. In the Dunstan study participants walked at just 3.2 km/h (2 mph),  which is a leisurely stroll for most able-bodied individuals.  In addition, participants were asked to identify how hard they were walking in the light intensity condition using the Borg scale.  The scale goes from 6 to 20, with 6 being “no exertion at all” and 20 being “maximal exertion”.  The average rating was 8, which falls between “extremely light” and “very light”.  In other words, these participants were not “exercising” in any way – they were just standing up and walking around at a very easy pace, just as you might when walking from your desk to the washroom.

These studies are of particular interest to me since my thesis work is examining similar issues in children.  With any luck I will have some data to report from that study later this year.  Along with other members of our research group I have also recently completed a systematic review on the acute impact of sedentary behaviour, which found a surprisingly large body of evidence linking short bouts of sedentary behaviour with increased metabolic risk (e.g. reduced insulin sensitivity and increased fat levels in the blood).  That review is currently in press, although it is currently available as a provisional pdf for those who don’t mind the formatting.

For those interested in learning more about the new study by Dr Dunstan and colleagues in Australia, I have embedded below a presentation by Dr Neville Owen who co-authored the above paper.  Thanks to Dr Owen and SBRN member Ernesto Ramirez for recording the session and making it available online.  And if you are interested in learning more about the impact of acute and chronic bouts of sedentary behaviour, be sure to check out the Sedentary Behaviour Research Network.

Travis

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ResearchBlogging.orgDunstan, D., Kingwell, B., Larsen, R., Healy, G., Cerin, E., Hamilton, M., Shaw, J., Bertovic, D., Zimmet, P., Salmon, J., & Owen, N. (2012). Breaking Up Prolonged Sitting Reduces Postprandial Glucose and Insulin Responses Diabetes Care DOI: 10.2337/dc11-1931

Nygaard, H., Tomten, S., & Høstmark, A. (2009). Slow postmeal walking reduces postprandial glycemia in middle-aged women Applied Physiology, Nutrition, and Metabolism, 34 (6), 1087-1092 DOI: 10.1139/H09-110

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31 Responses to Sitting for just a couple hours has measurable (and negative) health impact

  1. Lisa says:

    I’m wondering about the practical aspects of getting up once every 20 minutes for most office workers, especially knowledge workers or those in IT. I’d like to see this repeated with different parameters, like getting up once every 60 minutes for various durations (2 minutes, 5 minutes).

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    • Travis says:

      I’d love to see that too, although I think it may be some time before we have enough data from enough studies to be able to compare all those various setups (it gets harder and harder to justify the expense and time-commitment necessary to look at all the various permutations). Standing briefly every 20 minutes seems pretty reasonable to me (as someone who works an office job). Sending something to the printer, going to fill up a water bottle, etc, could easily justify that type of short walk.

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    • Duff says:

      A large number of office workers work according to the Pomodoro schedule of 25 minute periods:

      http://www.pomodorotechnique.com/

      Most people find this method significantly increases productivity.

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  2. I use a 20-minute timer on my desktop (http://e.ggtimer.com/ … it’s great!). I’ve been doing this for several months to rehab my back, and I am anticipating keeping it for the apparent benefits to my metabolism (and hence my weight loss).

    On a forum I’m on, IT folk have said that breaking their concentration would be a problem. And I do periodically get involved in something and I don’t pay attention to the timer.

    But I think that the net of doing this more often than not works. That and of course trying to do as many glute squeezes as I can when I think about it ;).

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  3. Carlin says:

    I gave up my chair. I built a standing desk and love it. I would be interested in a study that compares those that stand to work using the same test. I too work in IT and find that when standing I move around more, I am more focused and more productive. Others have had reduced back problems.

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    • The folks at Cornell point out that standing to work has its own concerns. I think a treadmill desk may be the ideal … but I do what they suggest. Sit to work and move frequently.

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      • Travis says:

        I’ve seen that piece, and I’ve asked if they’d be interested in doing a short point/counterpoint on the pros and cons of standing desks but have yet to hear back. My personal view is that it’s best to have the option to sit or stand (depending on your mood and the task at hand), which allows you to avoid sitting or standing for too long at a stretch. I’d certainly be interested in chatting more with folks that have an ergo/biomech background though.

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  4. Kent Burden says:

    Another facinating study on this subject. Dr Peter Katzmarazyk did a similar study back in 2009. The thing I find most interesting is many of these studies seem to indicate that doing 30-60 minutes of exercise have little affect. But short bouts of standing or light movement done regularly over the course of the day do. I wrote a book on this subject called Is Your Chair Killing You. The research is all really new but its growing and seems to be pointing in the same general direction.

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    • Travis says:

      Peter’s study on sitting and mortality was one of the first I read about sedentary behaviour and I cite it often!

      Unfortunately there really aren’t that many studies looking at activity throughout the day vs 1 or 2 large bouts. Some epidemiological stuff suggesting that taking breaks from sitting is beneficial, but that’s about it so far (at least that I’ve seen). But hopefully there will be more soon.

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      • Kent Burden says:

        For my book I cobbled together all the studies I could find on the subject. With all the sitting we do in today’s society and the heart disease, obesity and diabetic rates, it certainly seems like a subject that should be continue to be studied.

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  7. Kip Hansen says:

    Apparently, drinking high glucose/high fat drinks ['(for reference, that’s about the same as a medium McDonald’s triple-thick milkshake),'] before sitting down at your desk raises your plasma glucose levels, as one would suspect, but that getting a little intermittent exercise helps regulate the spike a bit.

    The purported ’20%!’ does not show up in the ‘Glucose area-under-the curve’ chart.

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    • Travis says:

      Actually, the purported 20% *does* show up in that figure. If you take the area under the curve of the “sitting without interruptions” condition, it is more than 20% bigger than the area under the curve of the other two conditions (or, you can look at it as the average glucose level being 20% higher on that day). That’s how area under the curve is measured.

      While you may not consume that type of liquid meal everyday, it nonetheless suggests that the body is becoming more insulin resistant during periods of extended sitting. That’s still a very bad thing.

      And remember, it wasn’t short bouts of exercise that mattered here – it was short bouts of walking at an extremely light intensity. That may seem like semantics, but there’s a big difference between telling someone to do 2 minutes of exercise and simply taking a 2 minute walk down the hallway.

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      • Kent Burden says:

        I agree with that last part. Much easier to get people in the office environment to do light movements like walking, stretching or balancing than it is too get them to do exercises.

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  8. Edgar Manhattan says:

    When you observe the physics of sitting, you see that the front of the lower abdomen shortens, and the overall girth of the lower abdomen front to back increases. This is especially pronounced in stout people, who were chosen for this study.

    Were the subjects wearing loose garments which adjusted easily to this topological change? Or were they wearing typical Western clothes which have belts or waistbands which artificially constrict the expanded lower abdomen while sitting?

    I haven’t seen this simple variable discussed in this or in previous similar studies. It’s very likely that belts or other waist-constricting clothing items will have a large impact on the physiological results of sitting, and the study may, in fact, merely be telling us that it’s unhealthy to wear waist-constricting clothes while sitting, not that sitting itself is intrinsically unhealthy.

    Before coming to any conclusions, a further study comparing the physiological results of the same group taking the same actions, but doing so with normal Western clothing for one set of tests, and perhaps loose fitting unbelted robes for another set of identical tests.

    Is it the sitting or is it the constricting belts or waistbands that are causing these effects?

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    • Travis says:

      Any reason why we would expect a tight waistband to have an impact on glycemic control? We have pretty good mechanisms to explain how changes in skeletal muscle could underlie these changes, but I can’t think of any related to constricted clothing.

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      • Edgar Manhattan says:

        In my first post I did not mean to imply that sitting by itself has no effect on body function, I was just pointing out that an important variable had not been accounted for in the study.

        The only way to answer most questions, including yours, is to experiment.

        In a biological system which relies on circulating fluids and nervous system signals to work properly, anything which is puts substantial pressure on blood vessels and nerves in the trunk is worth examining. We’ve all heard the cautionary tales about Victorian women’s illnesses which were caused by being winched into tight corsets – this is not a new phenomenon, it is just not being taken into account in this and previous similar studies.

        If studies are run which test this variable, I think it is very likely that some effects in the current study will be due to undo constriction, other effects will be due to sitting itself, and the origin and intensities of a third group of effects will be derived from a combination of sitting and constriction – and we will have learned some interesting and useful things.

        A snug belt on most standing men will become a very tight belt when the same man sits and that part of his body tries to occupy more space. The more plump he is, the greater the effect.

        Please note the ordinary Australian casual clothes, including a wide belt, worn by Nelville Owen in the videos. It’s quite snug while he’s standing, and will definitely constrict his lower abdomen when he sits, as you can see when he bends forward. Is he even aware of this? Or is he unaware of this particular cultural constraint which may have tainted his data?

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        • Edgar Manhattan says:

          For “which is puts” above, please read “which puts”, and for “undo” above, please read “undue”. For the latter, I had just re-watched the video, and the back of my mind was probably thinking Professor Owen should undo his belt a bit, it does look tight.

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          • Travis says:

            The only way to answer most questions, including yours, is to experiment.

            True enough. Although in practice we have limited resources so we need to focus on the factors that have some reasonable probability of having a physiological effect (and belt tightening doesn’t really meet this criteria, at least given what we know right now).

            For what it’s worth, there are many studies that have looked at the impact of bed rest (which would not cause belt tightening), which have found impacts similar to those in these studies looking at sitting.

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  11. Clay Vollers says:

    I can’t site the study, but I remember seeing that the male brain processed information about 7% faster when standing (thinking on your feet, Management By Walking Around, etc). Maybe. the hunter/gatherer treadmill desk isn’t such a bad idea.

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  12. julie says:

    I guess I’m lucky in my job, I rarely sit more than 15 minutes unless I’m in a meeting, otherwise I wander from my desk to my lab to different labs to stock rooms and back again, repeatedly. I do lay around mostly after 8 pm or so, but probably still up every half hour at least for bathroom, water, to see what strange animal is making noise (my possum resident), yell at neighbor’s dog, etc.

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  15. Michelle says:

    I am a bit late on this one, however for what its worth, let me give my 2 cents worth. I have been working with computers for a long time so you know that will involve a lot of sitting. Well because I am a bit overweight it has had really bad effect on me. I have damaged nerves in my legs fro them being compress to the chair all the time.

    I have also done irrepairable damage to both my legs as far as circulation goes. A lot of the thing you all are saying here I had no clue about or I would have put then into practice and not be how I am now….

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