Is all sitting equally bad?
Too much sitting around is bad for you—that’s, by now, a familiar refrain after several years of research findings. It’s not just the absence of exercise; when you don’t contract your muscles for several hours at a time, negative metabolic changes start to happen that can’t be counteracted with a trip to the gym.
But is all sitting the same? Is burrowing into the sofa to watch TV the same as sitting at your desk at work? That’s what a new study from researchers at several universities, led by Columbia University’s Keith Diaz, tried to find out in a new study published in The International Journal of Behavioral Nutrition and Physical Activity.
The study involved 3,410 African American adults in Mississippi, America, who completed a series of surveys and had the thickness of their carotid artery walls measured with ultrasound, which is a good early measure of heart-disease risk.
The surveys measured both TV viewing time (in increments of two hours per day) and sedentary time at work (never, seldom, sometimes, often, always), as well as levels of physical activity.
For TV time, the results were as expected: The more TV the subjects watched, the thicker their artery walls, regardless of how much they exercised. But the same wasn’t true for workplace sitting—in fact, those who sat more at work seemed to have better arteries, even after adjusting for factors like income and level of education.
What does this mean? Well, it suggests that the nature of your sitting time matters. The researchers point out that TV time is often completely uninterrupted and may directly follow high-calorie meals like dinner (and, I’d add, be accompanied by snacking). Workplace sitting, on the other hand, is more likely to involve getting up periodically to go to the printer or talk to a colleague, and less likely to involve Cheetos.
(Another thought that occurs to me but isn’t addressed in the paper: Is lying on the couch different from sitting at a desk chair?)
One caveat is that the study used questionnaires rather than wearable accelerometers to measure sedentary time. I’d be more confident in drawing conclusions about workplace sitting if the data was objectively measured.
Another is that there are potential confounding factors: Those who watched more TV tended to be older, less educated, and make less money, while those who sat more at work tended to be younger and more likely to be employed full-time. The researchers adjusted the results to try to account for these differences, but such statistical adjustments aren’t necessarily perfect.
In the end, the results are consistent with previous studies suggesting that short breaks in sedentary time may make a big difference. In practical terms, it suggests that people might want to worry more about their TV time than their desk-chair time. That seems like a hard sell—standing desks may have achieved reasonable popularity, but I have a tough time envisioning a boom in standing couches and treadmill TVs.
I’d also guess that the different types of sedentary time could be subdivided even further. Do you work at home or in an office? Is your work primarily solitary or collaborative? Do you meet with clients in person or by phone? All these factors will affect how unbroken your sedentary time is. We don’t need to micro-engineer different approaches for every possible work pattern. Instead, we need to keep the big principles in mind: If you haven’t moved a muscle in the last few hours, it’s probably time to get up.
