> For all you deluded ones who believe that sitting instead of daily life is 
> Zen. 


> Can sitting too much kill you?
> By Travis Saunders | Jan 6, 2011 10:39 AM
> We all know that physical activity is important for good health—regardless of 
> your age, gender or body weight, living an active lifestyle can improve your 
> quality of life and dramatically reduce your risk of death and disease. But 
> even if you are meeting current physical activity guidelines by exercising 
> for one hour per day (something few Americans manage on a consistent basis), 
> that leaves 15 to 16 hours per day when you are not being active. Does it 
> matter how you spend those hours, which account for more than 90% of your 
> day? For example, does it matter whether you spend those 16 hours sitting on 
> your butt, versus standing or walking at a leisurely pace? Fortunately or 
> unfortunately, new evidence suggests that it does matter, and in a big way.
> What is sedentary behavior?
> Before we go any further, it’s important that we define the term "sedentary 
> behavior". Sedentary behavior is typically defined as any behavior with an 
> exceedingly low energy expenditure (defined as <1.5 metabolic equivalents). 
> In general, this means that almost any time you are sitting (e.g. working on 
> a computer, watching TV, driving) or lying down, you are engaging in 
> sedentary behavior. There are a few notable exceptions when you can be 
> sitting or lying down but still expend high energy expenditure (e.g. riding a 
> stationary bike), but in general if you are sitting down, you are being 
> sedentary.
> The above definition may seem rather intuitive, but this is not the way that 
> the term sedentary has been used by exercise science researchers for the past 
> 50 years. Up until very recently, referring to someone as sedentary meant 
> simply that they were not meeting current guidelines for physical activity. 
> In simple terms, if you were exercising for 60+ minutes/day, you were 
> considered physically active. If you were exercising 10 minutes/day, you were 
> sedentary. Case closed. But as we will discuss below, sedentary time is 
> closely associated with health risk regardless of how much physical activity 
> you perform on a daily basis. Further, it is entirely possible to meet 
> current physical activity guidelines while still being incredibly sedentary. 
> Thus, to quote researcher Marc Hamilton, sitting too much is not the same as 
> exercising too little. (if you take only one thing from this post, let it be 
> that quote from Dr Hamilton). Which is why it is so important that when we 
> use the term "sedentary", we are all on the same page about what that means.
> Now that we know what sedentary behavior is, let’s look at its relationship 
> with health risk.
> Epidemiological Evidence
> In 2009 Dr Peter Katzmarzyk and colleagues at the Pennington Biomedical 
> Research Center published an influential longitudinal paper examining the 
> links between time spent sitting and mortality in a sample of more than 
> 17,000 Canadians (available here). Not surprisingly, they report that time 
> spent sitting was associated with increased risk of all-cause and 
> cardiovascular disease mortality (there was no association between sitting 
> and deaths due to cancer). But what is fascinating is that the relationship 
> between sitting time and mortality was independent of physical activity 
> levels. In fact, individuals who sat the most were roughly 50% more likely to 
> die during the follow-up period than individuals who sat the least, even 
> after controlling for age, smoking, and physical activity levels. Further 
> analyses suggested that the relationship between sitting time and mortality 
> was also independent of body weight. This suggests that all things being 
> equal (body weight, physical activity levels, smoking, alcohol intake, age, 
> and sex) the person who sits more is at a higher risk of death than the 
> person who sits less.
> The above findings linking excessive sitting with poor health are far from 
> isolated. For example, a similar longitudinal study from Australia reports 
> that each hour of daily television viewing (a proxy of sedentary time) is 
> associated with an 11% increase in the risk of all-cause mortality regardless 
> of age, sex, waist circumference, and physical activity level. And as my 
> colleagues and I summarize in a recent review paper (PDF), numerous 
> epidemiological studies have linked sedentary behavior with obesity, 
> cardiometabolic risk, and even some cancers.
> New evidence also suggests that in addition to the quantity of sedentary 
> time, the quality of sedentary time may also have an important health impact. 
> For example, Genevieve Healy and colleagues examined this issue in 
> participants of the Australian Diabetes, Obesity and Lifestyle (AusDiab) 
> Study. A total of 168 men and women aged 30-87 years wore an accelerometer 
> (an objective measure of bodily movement) during all waking hours for 7 
> consecutive days, which allowed the researchers to quantify the amount of 
> time that participants spent being sedentary, as well as how frequently they 
> interrupted these sedentary activities (e.g. standing, walking to the 
> washroom, etc).
> What did they find?
> The greater the number of breaks taken from sedentary behavior, the lower the 
> waist circumference, body mass index, as well as blood lipids and glucose 
> tolerance. This was true even if the total amount of sedentary time and 
> physical activity time were equal between individuals—the one who took breaks 
> more frequently during their time at the office or while watching television 
> was less obese and had better metabolic health. Importantly, the breaks taken 
> by the individuals in this study were of a brief duration (<5 min) and a low 
> intensity (such as walking to the washroom, or simply standing).
> Taken together, the epidemiological evidence strongly suggests that prolonged 
> sitting is an important health risk factor. But what explains these 
> relationships? Let’s now look at the multiple mechanisms linking sedentary 
> time with increased health risk.
> Mechanisms
> Reduced Energy Expenditure
> Quite obviously (and by definition), when you are sedentary, you are not 
> being physically active. And so one common assumption is that people who sit 
> more are at increased health risk simply because they are getting less 
> physical activity. However, somewhat surprisingly, sitting time and physical 
> activity do not appear to be related for most people. For example a paper 
> from the European Youth Heart Study published in PLoS Medicine reports no 
> association between physical activity and TV watching in a sample of nearly 
> 2000 children and teenagers, and other reports suggest that there is little 
> evidence that sedentary behavior displaces moderate or vigorous physical 
> activity. So while it makes intuitive sense that being sedentary reduces 
> energy expenditure, it is likely through the reduction of very light 
> intensity physical activity (e.g. standing, walking at a slow pace), rather 
> than by reducing the volume of what we typically think of as exercise. This 
> may also help explain why the relationship between sedentary behavior and 
> health risk are often independent of moderate or vigorous physical activity.
> Increased Food Intake
> In addition to reducing our energy expenditure, sedentary behaviors may also 
> promote excess food intake. For example, a recently published study in the 
> American Journal of Public Health suggests that the  amount of commercial 
> television (e.g. television with advertisements) that children watch before 
> the age of 6 is associated with increased body weight 5 years down the road, 
> even after adjustment for other important variables including physical 
> activity, socio-economic status and mother’s BMI. In contrast, watching 
> non-commercial television (DVD’s or TV programs without commercials) showed 
> no association with body weight. Similarly, it has also been reported that 
> each hour of daily television watching in children is associated with an 
> increased consumption of 167 calories per day (PDF), mainly through increased 
> consumption of high calorie, low nutrient foods (e.g. the foods most commonly 
> advertised on television). Much of this is likely just a learned 
> behavior—watching TV exposes us to food ads promoting unhealthy fare, which 
> is likely to have a disproportionate influence on younger viewers. Just as 
> importantly, people may just really enjoy munching on food while relaxing on 
> the couch. Either way, excess sitting (and TV watching in particular) seems 
> to put us in situations where we choose to eat more than we would otherwise.
> Physiological Adaptations
> I don’t think the mechanisms described above—that sitting too much may lead 
> to reduced energy expenditure and increased food intake—will come as much of 
> a surprise. But what I find truly fascinating is that sedentary behavior also 
> results in rapid and dramatic changes in skeletal muscle. For example, in rat 
> models, it has been shown that just 1 day of complete rest results in 
> dramatic reductions in muscle triglyceride uptake, as well as reductions in 
> HDL cholesterol (the good cholesterol). And in healthy human subjects, just 5 
> days of bed rest has been shown to result in increased plasma triglycerides 
> and LDL cholesterol, as well as increased insulin resistance—all very bad 
> things. And these weren’t small changes—triglyceride levels increased by 35%, 
> and insulin resistance by 50%!
> These negative changes are likely related to reductions in the activity of 
> lipoprotein lipase, an enzyme which allows muscle to uptake fat, thereby 
> reducing the amount of fat circulating in the blood (it also strongly 
> influences cholesterol levels—the details can be found here). Animal research 
> has shown that lipoprotein lipase activity is reduced dramatically after just 
> six hours of sedentary behavior—not unlike a typical day at work or school 
> for many individuals. Sedentary behavior may also reduce glucose transporter 
> protein content in the muscle, making it more difficult for glucose to be 
> taken into the muscle and resulting in higher blood sugar levels. What is 
> most interesting to me personally is that these physiological changes in 
> skeletal muscle have little or nothing to do with the accumulation of body 
> fat, and occur under extremely rapid time-frames. This means that both lean 
> and obese individuals, and even those with otherwise active lifestyles, are 
> at increased health risk when they spend excessive amounts of time sitting 
> down.
> Should we be concerned about the health impact of sedentary behavior?
> Yes.
> Western society is built around sitting. We sit at work, we sit at school, we 
> sit at home, and we sit in our cars as we commute back and forth. In fact, a 
> recent survey reports that the average American accumulates more than 8 hours 
> of sedentary behavior every day—roughly half of their waking hours. The 
> situation in children is, unfortunately, no different. There is evidence that 
> children in both Canada and the USA (PDF) accumulate more than 6 hours of 
> screen-time (time spent in front of the TV, computer, or other screen-based 
> device) on a daily basis. Keep in mind that screen-time is almost exclusively 
> sedentary (active video games excluded), and that all these hours of 
> sedentary behavior are in addition to the hours and hours (and hours) that 
> kids spend sitting at school. In fact, a recent study reports that roughly 
> 70% of class time, including physical education class, is completely 
> sedentary (while slightly better than class time, children were also 
> sedentary for the majority of lunch and recess).
> In short, given the consistent links between sedentary behavior and both 
> death and disease, and the ubiquity of sedentary behavior in our society, we 
> should be very concerned about the health impact of sedentary behavior.
> What is the take-home message?
> There is a rapidly accumulating body of evidence which suggests that 
> prolonged sitting is very bad for our health, even for lean and otherwise 
> physically active individuals. The good news? Animal research suggests that 
> simply walking at a leisurely pace may be enough to rapidly undo the 
> metabolic damage associated with prolonged sitting, a finding which is 
> supported by epidemiological work in humans. So, while there are a lot of 
> questions that remain unanswered (e.g. Is there a “safe” amount of daily 
> sedentary time?), the evidence seems clear that we should strive to limit the 
> amount of time we spend sitting. And when we do have to sit for extended 
> periods of time (which, let’s face it, is pretty much every single day for 
> many of us) we should take short breaks whenever possible.
> Finally, if you take only one thing from this post, let it be this—sitting 
> too much is not the same as exercising too little.

Reply via email to