Thanks for sharing this!  k

--- On Thu, 1/13/11, Edgar Owen <> wrote:

From: Edgar Owen <>
Subject: [Zen] News: Can sitting too much kill you?
Date: Thursday, January 13, 2011, 5:22 AM


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 
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.
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?
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.


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