Sedentary Physiology Part 2 – Can Sitting Too Much Kill You?

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Welcome to our 5-part series delving into the fascinating research being performed in the emerging field of sedentary physiology.  Today in Part 2, we look at some of the health effects associated with excess sedentary behaviour.  For an introduction to the basics of sedentary physiology, check out Part 1.

Over the past few years research has suggested that being sedentary (e.g. sitting or lying down) for extended periods of time has a negative impact on your health. We know that people who sit for long periods of time are less likely to be physically active, and more likely to be obese, so it’s not that surprising that people who sit for extended periods of time would have increased health risk relative to people who sit less. But new research is suggesting that people who spend more time seated are at increased health risk even after control for these other factors. In other words, no matter your body weight or how much you exercise, sitting too much still results in increased health risk.

For example, a recent study by Canadian researchers published in Medicine and Science in Sport and Exercise looks at this very topic. The study, available here, was performed by Peter Katzmarzyk (a former instructor of both Peter J and myself during our time at Queen’s) and colleagues at the Pennington Biomedical Research Center, and examined the links between time spent sitting (at school, work, and at home) and mortality in a representative sample of more than 17,000 Canadians. 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 cancer deaths). 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.

But wait – could it be that the people who sit more are only at risk because they also happen to be obese? Unfortunately body weight was only available in a subset of individuals in the present study, making this a difficult question to address. However, the authors did examine the association between sitting and mortality after control for body weight in this subset of individuals, and report that sitting remained a significant predictor of mortality. 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 authors go on to suggest that sitting for extended periods of time may alter certain physiological processes, such as lipoprotein lipase activity, which could explain the link between time spent sitting and mortality risk (we’ll get to this in Part 4 of the series!).

These findings linking sedentary behaviour with poor health are far from isolated.  For example, a similar 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. And as we summarize in a review paper published earlier this month, numerous epidemiological studies have linked sedentary behaviour with obesity, cardiometabolic risk, and even some cancers.

As you can see, the evidence is piling up that total sedentary time is a consistent predictor of negative health outcomes.  But does it matter how you accumulate that sedentary time?  For example, does sitting for 2 hours straight have the same health impact as sitting for 2 hours total, but with one hour of physical activity in the middle?  Be sure to check-in tomorrow for Part 3 (now online!) in our series to find out!

Travis

Katzmarzyk, P.T., Church, T.S., Craig, C.L., & Bouchard, C. (2009). Sitting Time and Mortality from All Causes, Cardiovascular Disease, and Cancer Medicine and Science in Sports and Exercise, 41 (5), 998-1005

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