The Science behind “Sitting Disease”

This is an excerpt from the forthcoming “Scared Sitless: The Office Fitness Book.”

Sitting Disease ResearchWhen you look at the science behind the numerous news headlines about “sitting disease” you find three major bodies of research. First are epidemiological, population-level studies that look at large numbers of sitters and non-sitters and report on their overall health. Second are studies that look at the troublesome physiological mechanisms associated with sitting, the underlying causes of the “sitting disease” identified in the population studies. Finally, in a much newer body of literature, scientists have looked at the effectiveness of specific interventions that limit sedentary time. Let’s look at some of the major findings in each of these areas.

First, though, it’s worth pausing for a moment to think about the consequences of the diseases for which sitting puts you at risk. I don’t want to get too graphic, but it’s worth reflecting on the fact that cancer, diabetes, and heart disease are horrific diseases that not only lop years off of your life but also dramatically reduce the quality of your life. This research shows that taking care of yourself now can mean the difference between living a long, productive, care-free life and a shorter life filled with more doctor visits and hospital stays, as well as diminished physical capacity. These risks, of course, apply just as much to other health choices that you make. But the evidence below shows that, if you have a desk job, improving your office fitness is arguably the most important improvement you can make to enhance your long-term health prospects.

Enough with the fear-mongering. On to the research.

Population-Level Research

Epidemiological Research on Sitting DiseaseIn 1953 Jeremy Morris and his colleagues in London compared the health of trolley drivers and conductors. Both worked the same hours in the same double-decker trolleys, but the drivers sat all day while the conductors were standing and moving most of the time. The more sedentary drivers were twice as likely to get heart disease as the standing, walking, stair-climbing conductors. Morris also observed similar differences between more active “postmen” and less active “telephonists, executive officers, and clerks.” His conclusion: “Men in physically active jobs have a lower incidence of coronary heart-disease in middle age than have men in physically inactive jobs. Moreover, what disease the conductors and postmen had was less severe.“ This study arguably launched the modern field of sedentary studies.

There had been a few random looks into the field before Morris’s work. As early as the late 17th Century, the Italian occupational-medicine pioneer Bernardino Ramazzini had noted that messengers who ran from place all day had fewer diseases than sedentary cobblers and tailors. In the late 18th Century, researchers in London replicated Ramazzini’s findings and also compared the health of other sedentary and non-sedentary workers and found similar results. And in the early 20th Century American doctors began to note an association between physical work and improved health. But it was the publication of Morris’s findings in 1953 that really started the rigorous, scientific, ongoing study of sedentary behavior. Morris continued his studies for nearly 50 more years, working well into his eighties and living to the age of 99. Given his long life and knowing his research interests, we can reasonably assume that even as he pursued a scholarly life he somehow managed to remain routinely active at work.The epidemiological case against sitting has grown considerably since Morris’s time.

The next big wave of sedentary-studies activity began with research on TV-watching couch potatoes. In 1985, William Dietz asked in the journal Pediatrics, “Do we fatten our children at the television set?” He found that television viewing was a likely cause of obesity in children and adolescents. In 1996, Stephen Sidney and his colleagues reported in the Annals of Epidemiology journal that “heavy TV viewing is a modifiable behavior that is associated with increased prevalence of several cardiovascular risk factors.” In 2000, Jo Salmon and her colleagues at Deakin University in Australia said that “public health strategies to reduce overweight and prevent weight gain may need to focus on reducing sedentary behaviors such as television viewing in addition to increasing physical activity” A 2001 study by Frank Hu and his colleagues suggested in the New England Journal of Medicine “the importance of reducing sedentary behavior in the prevention of type 2 diabetes.” Adrian Cameron and a large team of researchers reported in 2003 on the 1999-2000 Australian Diabetes, Obesity and Lifestyle Study. They found strong associations between obesity and both television viewing time and lower physical activity time that “confirm the influence of sedentary lifestyles on obesity.” A similar large study by David Dunstan and another large team in Australia reported in 2010 that “television viewing time is associated with an increased risk of all-cause and CVD [cardiovascular disease] mortality.” A 2008 study by Genevieve Healy showed that even very active people who met recommendations for regular exercise had increased metabolic risk factors that rose with TV viewing time. These are just a few of dozens, if not hundreds, of studies that link prolonged sitting in front of a television to obesity, cancer, heart disease, diabetes, and other serious diseases.

Beginning in the 1990’s and up until today, researchers have looked beyond television watchers, turning to the more generic problem of physical inactivity. Much of this research arose around the observation that sedentary behavior appeared to be an independent risk factor, a problem regardless of your weight, exercise habits, or other fitness measures. In 1999, Steven Blair and Suzanne Brodney found that you can carry a few extra pounds but sill be better off than a thin person who sits all day, or as they put it, “Overweight or obese individuals who are active and fit are less likely to develop obesity-related chronic diseases and have early death than normal weight persons who lead sedentary lives.” In 2006, Lyn Steffen and her colleagues noted in their findings from the Minnesota Heart Survey that from 1980-2000 people reported the same amounts of exercise activity but more sedentary time at work. “It is significant that one easily identifiable sedentary activity, namely, sitting at work (instead of standing), increased markedly over 20 years and that, interestingly, men and women who sat less than half the time at work had a lower BMI [body mass index] than those who sat more than half the time.” In 2009, Neville Owen and his colleagues reported in their paper “Too much sitting: a novel and important predictor of chronic disease risk?” that “even if people meet the current recommendation of 30 minutes of physical activity on most days each week, there may be significant adverse metabolic and health effects from prolonged sitting.“ Also in 2009, Peter Katzmarzyk and his colleagues found “a dose-response association [i.e., more of it is worse] between sitting time and mortality from all causes and CVD [cardiovascular disease], independent of leisure time physical activity” and urged physicians to “discourage sitting for extended periods.”

I could go on – there are literally hundreds of other studies I could cite (many of them listed in the bibliography) – but you get the idea: Sitting is a huge public health problem. And, unfortunately, it is likely to remain so. As Marc Hamilton said in a 2007 paper in the journal Diabetes, “Given the increasing pace of technological change in domestic, community, and workplace environments, modern humans may still not have reached the historical pinnacle of physical inactivity.”

Inactivity-Physiology Research

Inactivity Physiology Research on Sitting DiseaseMarc Hamilton is not just a sedentary-studies prognosticator. He is also the leading pioneer in “inactivity physiology,” a new field that looks at the physiological mechanisms that underlie “sitting disease.” Epidemiologists have shown that sitting is a problem. Hamilton and his crowd show how it is a problem.

Hamilton coined the phrase “inactivity physiology.” A few key concepts have already emerged in this nascent field:

  • “Humans naturally require a large amount of time in physical activity throughout the whole day for good health.” Forty-five minutes of exercise can’t offset ten hours of sitting. You need to move throughout the day.
  • We don’t spend enough time each day doing any physical activity. It is this absence of any muscular inactivity that underlies the unique physiological problems of sitting.
  • “The signals harming the body during physical inactivity are specific and distinct from exercise.” Too much sitting is not the same as too little exercise.

Even before Hamilton coined the phrase in 2004, researchers were already looking at “inactivity physiology” (even if they weren’t calling it that then). Much of the early research in this area came out of the air and space fields, where there is plenty of sitting and inactivity. In the early 1980s, for example, aviation-industry researchers curious about the impact of long-term airline flights found blood-pooling in the calves of people who sat for prolonged periods. Beginning in the 1990s, Joan Vernikos and her colleagues at NASA conducted experiments in which they tried to mimic the weightlessness of space with bed rest, culminating in a paper in 2010 that showed how space travel accelerates the aging process. Vernikos worries now that our sedentary ways may be accelerating the aging of sedentary office workers. Exercise physiologists and others have, of course, also looked at the problems of inactivity.

The upshot of all of this research is a long list of physiological problems associated with sitting. Let’s look at some of them.

As soon as you sit down, electrical activity in your muscles drops almost immediately. In a 2011 article in the New York Times, Hamilton said, “The muscles go as silent as those of a dead horse.” Along with the drop in electrical activity comes a decrease in the release from your muscles of enzymes that help regulate blood cholesterol levels. “Good” cholesterol (HDL) levels decrease and “bad” cholesterol (LDL) levels increase, putting you at increased risk for atherosclerosis. The deep muscles that help us stand up and maintain a vertical posture also release enzymes that help regulate your cholesterol levels. As soon as you sit down, you turn off this mechanism. Hamilton is probably the best-known researcher in this area, and he and his colleagues have conducted much of the research on the role of postural muscles in regulating cholesterol levels, which they have shown is related to the regulation of lipoprotein lipase (LPL). When sitting, you burn calories at a much lower rate then when you are standing or walking, putting you at risk for obesity. Another sedentary studies pioneer, James Levine at the Mayo Clinic, estimates that you burn somewhere between 700 and 1000 calories in the typical office job if you sit most of the day and about 1400 calories if you stand most of the day (compared with 2,300 calories in strenuous occupations like farming). Following this math, simply standing instead of sitting most of the day burns enough calories to help you lose about 10 pounds a year, and walking at a leisurely two miles per hour on a treadmill desk could help you lose 40. Going upstream, back to the start of someone’s office career, you can see the almost-immediate impact of burning fewer calories. One study, for example, looked at the effects of sedentary work on previously active employees and found that the typical new office employee puts on 16 pounds within 8 months of starting a sedentary desk job.

When you increase your sitting time and reduce your moving time, your body’s insulin action, its ability to process glucose, drops significantly, putting you at risk for diabetes. One study found that having non-exercising men reduce their daily number of steps taken from 10,000 to 1,500 for just two weeks significantly reduced their insulin action. Another found that “a single day of prolonged sitting can dramatically reduce insulin action in healthy young adults.” A 2013 John Buckley and his colleagues in the UK conducted the first study that looked specifically at the effects of sitting in an actual office setting. They found a 43% improvement in blood glucose levels when office workers stood at work (they also found that standing workers burned about 50 more calories per hour when they are standing).

Sitting has also been implicated in systemic inflammation, a prime suspect in many chronic diseases. A 2012 study found chronic low-grade inflammation in women in sedentary occupations (but, curiously, not in men). Given the growing interest in inflammation as a contributing factor in many serious diseases, I predict we’ll soon see more research on the role sitting and sedentary behavior on chronic inflammation.

When you sit down, your “second heart” –  deep muscles in your calves that help pump blood back up to your heart – is turned off, impairing your blood circulation. Those muscles have to be used to do their job, and they are shut down when you sit. Among the many problems this can causes is a very serious, potentially life-threatening condition called deep vein thrombosis. Sitting also also impairs microvascular function. Subtle, regular movements of your body help the tiny blood vessels in your arms and legs work properly. When you sit down and stop moving this microvascular activity drops dramatically, further impairing your circulation.

Sitting alters your body’s ability to regulate blood pressure. Joan Vernikos, the former head of Life Sciences at NASA, and her colleagues found that the motion of simply standing up activates mechanoreceptors in your neck that help regulate blood pressure. Plop down in your office chair and stay there for several hours and this mechanism never gets a chance to work.

Sitting physically shortens, lengthens, and otherwise distorts your muscles, tendons, and ligaments, and the fascia and other tissues around them, causing postural distortions that lead to everything from low-back pain to headaches. The muscles that flex your hips shorten up as you passively flex them in your chair, causing back trouble when stand up. Your back muscles turn off, causing passive structures like ligaments and intervertebral disks to take up the slack in an attempt to hold you upright, leading to back pain and other conditions. Your intervertebral disk, the big thick pads between each pair of bones in your spine, need regular movement to nourish them, and sitting, of course, prevents this. Adding insult to injury, your hamstrings and buttocks are crushed between your torso above and a poorly designed office chair below. I’ll talk much more about these kinds of orthopedic issues later in this chapter as well as in the Posture chapter.

Finally, when you sit down the muscles that hold you upright flicker off and forget how to work properly, leaving you at risk for injury when you do try to use them. Perhaps the most dramatic example of this is a “weekend warrior” injury to an underused muscle that snaps under sudden exertion. Personal trainers who work with desk jockeys spend a lot of their time teaching chronic sitters to reengage muscles like these that have atrophied after years of misuse and neglect.

There are other physiological problems associated with sitting, and certainly others will be discovered, but I think you get the idea: Sitting all day is not kind to your body.

Intervention Research

Research on Sitting Disease InterventionsThere is a growing body of emerging research that looks at the effect of specific interventions designed to counteract the effects of sitting. This is a brand-new field, most of the research having been conducted in the past couple of years, so there is still much to be learned and discovered. So far, though, it looks like the hypothesis is sound that moving more and sitting less can improve your health.

Several studies have shown that breaking up sitting every 20 to 60 minutes with some kind of light or moderate physical activity like walking or bicycling reduces levels of biomarkers associated with diabetes. Teatske Altenburg, a sedentary studies researcher in The Netherlands, and her colleagues found that interrupting prolonged bouts of sitting with eight minutes of moderately intense bicycling every hour reduced levels of proteins associated with diabetes. Having both a bicycle and ten minutes free every hour isn’t typical for most office workers, of course. In a more realistically designed study, David Dunstan, a sedentary-studies researcher in Australia, found that taking a two-minute break every 20 minutes to do “light- or moderate-intensity walking lowers postprandial [after a meal] glucose and insulin levels in overweight/obese adults.” So, if you can somehow find a way to take a two-minute walk every twenty minutes (say, by sharing a treadmill desk with your colleagues), you can reduce your risk of diabetes.

Another study, the first of its kind, used a very similar intervention – two minutes of light activity every 20 minutes – to examine the effects of sitting on gene expression in muscles. Celine Latouche and her colleagues at the Baker IDI Heart and Diabetes Institute in Australia found that “breaking up sedentary time with short activity bouts is associated with changes in the expression of skeletal muscle genes involved in cellular development, growth and proliferation, and lipid and carbohydrate metabolism,” all of these beneficial. They also “observed similarities between genes regulated by breaks and by continuous acute exercise bouts of 30–90 minutes.” So, at least in terms of genetic expression, regular routine movement may offer benefits similar to those gained by vigorous exercise. By the way, I think the people in this study should be honored in some way, since the research included taking from each of them multiple biopsies, each biopsy entailing being cut open with a scalpel and then having a big needle passed through the opening to retrieve muscle tissue for analysis. Ouch!

One of the most common interventions proposed to break up our sitting days is the standing desk. An inordinate number of studies on standing desks have looked specifically at their effects on productivity. This meshes with anecdotal evidence that I have gathered in an amazing number of conversations that go like this: “Oh my God! If I stand up I’ll quit thinking,” and/or “I have to sit to think and get my best work done.” Is standing to work really as disruptive as trying to rub your belly and pat your head at the same time? The evidence does not support this fear. A 2009 study by Britta Husemann and her colleagues in Germany found that “a sit-stand workstation paradigm reduces musculoskeletal complaints without considerably affecting data entry efficiency.” A 2011 study by Christina Ohlinger and her colleagues at Miami University found evidence that you can indeed think and stand at the same time, demonstrating that standing workstations can “increase physical activity in the workplace without compromising cognitive capabilities.” Also at Miami University, Ronald Cox and his colleagues looked at people’s ability to speak while sitting, standing, and walking at one mile per hour on a treadmill and found no difference in their ability to speak clearly and grammatically, concluding that “the significant elevation of metabolic rate in the absence of any deterioration in speech quality or RPE [rating of perceived exertion] support the utility of using active work stations to increase physical activity in the work environment.” So it looks like you can safely stand, think, and even talk while using a standing desk.

Moving beyond concerns about productivity while standing, more recent research is testing whether people office workers will actually use standing desks and what the metabolic effects would be if they did. The first study to look specifically at this was a team at the University of Queensland in Australia. In 2012 they reported that when standing desks were made available most people in the office used them and replaced most of their sitting time with standing time. The only notable change in the biomarkers they examined was a significant increase in HDL (the “good” cholesterol) levels. A 2013 study at Curtin University in Australia replicated the finding that when standing desks were made available, office workers stood more. Also in 2013, another Australian team of researchers found that sitting time was reduced from 85% of the work day to 60% with the introduction of sit-stand desks in a government office in Sydney. Standing desks may not be for everyone, but it looks like a lot of people will use them if they’re available.

The other commonly proposed sitting intervention is, of course, the treadmill desk, a combined standing work station and low-speed treadmill that permit you to walk while you work. There have now been several studies that look specifically at treadmill desks in an office setting. As you would expect, there is evidence that you burn more calories when walking at work. For example, a 2008 study in the British Journal of Sports Medicine reported that treadmill desk users burned an extra 200 calories per day. The big hope, course, is that walking on a treadmill all day will help you get healthier and maybe even look better, and there is evidence of this as well. Researcher at the University of Massachusetts, for example, found that “favorably influenced waist and hip circumferences and lipid and metabolic profiles in overweight and obese office-workers.”

As with standing desks, many are concerned that productivity might decline at a treadmill desk. And indeed there is some evidence of this. Researchers at Miami University and at the University of Tennessee found that some fine motor skills (using a mouse, for example) were impaired while working at a treadmill desk (a 6-11% reduction in accuracy in a 2009 study in Tennessee) and that math skills were somewhat diminished. However, these studies found no negative effects on your ability to think, to focus, and to comprehend written works. And another study that looked at radiologists who evaluated CT scans and found that their analysis of those crucial images was just as good when they evaluated them while walking at a treadmill workstation. Many of these researchers note that these experiments are conducted over relatively short time spans, so some of the productivity declines they observed might be mitigated with more training and experience. For example, researchers at the Mayo Clinic recommended that transcriptionists receive more than the four hours of training that they were given for the experiment in order to optimize their productivity.

A couple of studies have looked at under-desk stepping and pedaling machines. The most detailed of these, a 2012 study by Lucas Carr and his colleagues at the Centers for Behavioral and Preventive Medicine in Rhode Island, gave full-time office workers under-desk pedaling machines and tracked their usage over four weeks. They found that, without any prompting other than the presence of the gadget, the experiment’s participants used it about a half hour every day and reported that it was comfortable and enjoyable and a good indoor exercise for rainy days. The study measured only time spent using the machines, not any of the biomarkers associated with sitting and exercise, and gathered just a little qualitative feedback from the participants, so much more research is needed on these machines. One concern that occurs to me is that they are used sitting down and that they have so far been used only episodically, making them more like an exercise intervention than a sedentariness-reduction intervention. It will be interesting to see whether and how future research untangles the independent threads of sitting versus exercise with this kind of intervention.

There is one other intervention on the horizon that I should mention. Pharmaceutical companies are developing a “metabolic polypill,” a medication that combines aspirin, statins (for managing cholesterol levels), and blood pressure-lowering agents. This pill is designed for patients at high risk for cardiovascular disease, but it has also been proposed as a remedy for “sitting disease.” Not surprisingly, many exercise-physiology researchers disagree with this idea. In a paper entitled “Exercise Is the Real Polypill,” Carmen Fiuza-Luces and her colleagues note that “regular exercise, a drug-free intervention, is available at low cost and relatively free of adverse effects” and that compared to exercise “no drug intervention has proven efficient to maintain muscle fitness, a key factor to ensure independent living throughout all stages of life.” A medication like the polypill might address some of the symptoms of your sitting condition, but it can’t help you stay strong and vigorous into your later years, as exercise can.

As you can see, there are plenty of problems with sitting and a nascent understanding of what to do about it. The rest of this book is about helping you do something about it, specifically to move more routinely at work, to at the very least sit less during your work day. As David Dunstan, the oft-cited Australian researcher points out, “Even in physically active adults, concurrent reductions in the amount of time spent sitting is likely to confer health benefits.” In other words, it’s time to get up off your derriere and get moving at work.

Are you standing up yet?

Comments

  1. Michael R. Wolf says

    After burning out as a “road warrior” and itinerant trainer, I took some “desk jobs” and found relief from jet lag but found that I could not concentrate as well, think as deeply, or verbalized my thoughts as clearly when I sat as when I was lecturing from a white board or walking among my seated students. This was not just the effect of going from communicating to coding. Even my coding was decreased if I remained seated, even in a multi-hundred dollar Herman Miller chair. A standing desk helped. So did installing a white board that could not be reached from my desk. Ideas would start flowing within just a few steps as I left my (standing or sitting) desk to walk around, use my arms and hands to draw, and physically and kinesthetically interact with my ideas and the physical world.

    To paraphrase John Medina in “Brain Rules”, our bodies evolved to work in near constant motion, and if we were to try to design the conditions that most hamper it’s optimal working conditions, we’d come up with the modern office and classroom.

    I now feel bad for placing all my students at such a disadvantage. I should have had them walk an listen instead of turning off their bodies and hobbling their brains.

    Here’s to the new walking office and moving classroom!

    • says

      I love the idea of getting your students up and moving, Michael. Let me know if you give that a try. I also love the white board idea, especially the fact that you have to stand up to use it.

      I’ve read dozens of accounts like yours of increased concentration, productivity, and inspiration when you’re on your feet and am looking forward to seeing your experiences supported by research soon.

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