You’ve heard it here more than once: sitting too much is bad for you. Unfortunately, much of our everyday life is comprised of prolonged sitting – from your car, to your desk, to your dining table, to your couch. There’s just no escaping the temptation to sit. Sometimes, despite your best efforts, sitting is the only socially acceptable option. (Ever tried standing in a movie theatre or at dinner in a restaurant? This guy has)
Sitting too much increases your risk of a variety of diseases and early mortality even if you are at a healthy weight and you regularly exercise. For instance, as Travis previously summarized, a “longitudinal study from Australia reports that each hour of daily television viewing is associated with an 11% increase in the risk of all-cause mortality regardless of age, sex, waist circumference, and physical activity level.”
Some have gone as far to suggest that sitting is the new smoking. How is that for an ominous metaphor?
In case you needed more proof that excess sitting is, in fact, killing you – here it is, courtesy of a new study published in the Journal of the National Cancer Institute: too much sitting is also associated with an increased risk of certain cancers.
In the study, the authors analyzed data from 43 individual studies including a total of 68 936 cancer cases (a study or studies, or a meta-analysis in science-geek parlance). Across all these studies they compared the risk of a specific cancer in the most versus the least sedentary group.
Comparing the highest levels of sedentary behavior to the lowest, the study observed a significantly higher risk for three types of cancers of the colon, endometrium, and lung.
Specifically, for each 2-hr increase in daily sitting time, the risk for colon cancer, endometrial cancer, and lung cancer, increased by 8%, 10%, and 6%, respectively.
Similar observations were reported for the specific behaviours of TV viewing time and occupational sitting time as well as total sitting time.
As has been described in other similar studies, these associations were true regardless of how much individuals exercised. In other words, not only do we all need to try to be physically active, we have to ensure we’re not falling into the category of an active couch-potato. That is, one who exercises for an hour a day, but spends the rest of his/her time with their butt firmly planted in a chair or couch.
As always, we have to keep in mind the limitations of this type of study. One of the first lessons we all learn in an entry statistics class is that correlation does not equal causation. An increased risk of certain cancers with increased idle time has been observed consistently across many studies, but this does not definitively prove that sitting causes cancer.
Nevertheless, limited lab studies in humans and animals have provided some insights into the mechanisms by which this might happen. The authors of this paper suggest a number of ways in which sitting may lead to cancer – with the mechanism potentially differing based on the type of cancer in discussion. At this point, however, the picture remains blurry.
What is less unclear is the fact that we’d all likely do ourselves a favour by spending less time on our ischial tuberosities (sitting bones).
Daniela Schmid, Michael F. Leitzmann. Television Viewing and Time Spent Sedentary in Relation to Cancer Risk: A Meta-analysis. Journal of National Cancer Institute. 2014. DOI:10.1093/jnci/dju098