8.5 Hours Of Daily Sitting Linked To Higher BMI And Cholesterol

This is Science Friday. I’m Kathleen Davis. Odds are that you’ve heard over the past few years that there’s a very common activity that’s not very good for us, and that’s sitting. Too much sitting has been linked to poor health outcomes, which can be scary for those of us who work at a desk most days. A recent study in the journal PLOS One sheds more light on just how much sitting is too much and the kind of health complications that are tied to that.

Here with me to explain are two authors of that study, Dr. Chandra Reynolds, Professor in the Institute of Behavioral Genetics at the University of Colorado in Boulder, also Professor Emeritus at the University of California, Riverside. And Ryan Bruellman, PhD candidate in genetics, genomics and bioinformatics at the University of California, Riverside. Welcome, both of you, to Science Friday.

RYAN BRUELLMAN: Yes. Thank you. It’s great to be here.

CHANDRA REYNOLDS: Thank you. Thank you for having us.

KATHLEEN DAVIS: OK. So Ryan, sitting has gotten a bad rap. There was this phrase that was going on a few years ago that sitting is the new smoking. What’s your perspective on this?

RYAN BRUELLMAN: Yeah, so there was a lot of information coming out about sitting and how bad is it? Is it, as you said, a lot of people wondered, is it the new smoking? But really, it’s just it’s another behavior to really just focus in on. There are many different behaviors that we do that form the puzzle pieces of our health. And I think sitting is one of those puzzle pieces, and just thinking about how much you’re sitting is something to really consider and really focus in on, really across your age range.

It doesn’t matter if you’re older or younger. It does matter throughout your entire lifespan.

KATHLEEN DAVIS: And why is sitting bad? Is it because of the specific position our body is in, or is it something else?

RYAN BRUELLMAN: So there are a multitude of different reasons for different things that can cause this. One of which could be just sitting for a long period of time in one position is not really– our body’s not really used to that. Some individuals might have felt this if they’ve been on a plane doing an international leg or across country. You get up, and it’s like, oh. You can feel it in your body. Your body is speaking to you and saying, hey, get up and move around at least a little bit.

KATHLEEN DAVIS: So, Chandra, your expertise is in aging. Is there a correlation between sitting and aging? I mean, why study these two things in tandem?

CHANDRA REYNOLDS: Yes. So I think sitting makes up a behavior that’s related to sedentary behavior. And we do know from studies that it’s more optimal to be engaging in physical activity compared to sedentary behavior. So there have been studies suggesting a link with less optimal health outcomes for individuals who are more sedentary and less active.

And so we wanted to see what this might look like at younger ages as well. Part of our perspective in the projects that we’re conducting is trying to understand how earlier life, including in early adulthood, how those might play out across the life course and impact how well we age.

KATHLEEN DAVIS: OK. So let’s get into this specific study that you two did together. Chandra, explain to me what you were looking at and who you were looking at.

CHANDRA REYNOLDS: Yes. So in this project, we engaged participants from the Colorado Adoption Twin Study of lifespan, behavioral development and cognitive aging, which we call cat’s life. And we had followed up about 1,300 individuals in their late 20s to 40s who’ve participated in earlier long term longitudinal studies, the Colorado Adoption Project and the Colorado Longitudinal Twin Study.

And part of our objective was to look at environments and experiences, including things like sitting behavior and physical activity and how these might relate to metabolic and other aspects of health. And part of our sample, as you can tell from the description, is that we include twins and siblings, and we wanted to enable us to rule out other factors that might be at play when we look at associations like the impact of sitting on health outcomes. And so studying twins, how they differ, enables us to rule out other things that might be at play, like genes or environments that individuals grew up in and really focus on behaviors like sitting.

KATHLEEN DAVIS: Can you parse that out a little bit more for people who might not be familiar with how twin studies work? Why is it that you’re able to glean maybe a different sort of information by using twins versus two people who are not related?

CHANDRA REYNOLDS: Certainly. So we did look at our entire sample too, as well. But then we focused in on the twins, in particular. And I think the most salient example are that identical twins share all of their genes in common and their shared rearing environment. So we’re controlling for some of those factors when we then look at differences among the identical twins and compare their similarities and differences in the behaviors of interest. So how similar are they in sitting, but how different are they in physical activity, for example.

So we can do some comparisons to see if there are impacts of things like sitting on health outcomes based on the comparison of the two twins, because this should, if it looks the same as when we look at all individuals, if it looks the same that the twin who’s sitting more has less optimal health outcomes than their co-twin, then this gives us a lens that it might be a exposure effect, environmental effect from that difference comparison.

KATHLEEN DAVIS: So tell me what you discovered in terms of if this sitting really is having a profound effect on health and how much sitting seems to be too much sitting.

CHANDRA REYNOLDS: So yeah. So prolonged sitting, we observed, is bad for heart health. And we focused in on more sitting, particularly above about 8.5 hours a day, coupled with less physical activity was associated with worse cholesterol ratio. And so that was one indication. And I’d love for maybe Ryan to follow up on this point, but our identical twin comparisons also showed this kind of pattern, but also some potential optimal effects of replacing sitting with vigorous exercise.

RYAN BRUELLMAN: The additional work that we were able to do with those identical twins, we looked at twins that differed in their behavior. So we had these identical twin pairs where one twin sat more than their respective co-twin, but maybe they got more physical activity. And we focused in on vigorous physical activity. So they got more vigorous physical activity compared to their co-twin.

So them sitting more but getting more exercise, we called them the compensators. And then we had these twin pairs where the twin that sat less got more vigorous physical activity. So compared to their co-twin, they’re replacing that sitting time with vigorous physical activity. What this analysis, this unique analysis that we could do showed us was that replacing that sitting time is optimal. However, if you’re not able to replace that sitting time, you can make up for higher levels of sitting time. It’s just you’re going to need to really amp up that vigorous physical activity likely past what, at least the current guidelines say.

KATHLEEN DAVIS: So do we know if it is sitting as opposed to lack of physical activity. If I just lay down all day, is that the same as sitting?

RYAN BRUELLMAN: Yeah. Our study is not particularly set up to parse apart the modes of sitting, per se, as far as those finer details. That would definitely need to be a call for further research, just to look at those different modes and finer details.

KATHLEEN DAVIS: Chandra, Ryan talked about this a little bit, but are the current guidelines for physical activity enough? Right now, I believe that’s about 20 minutes a day of moderate exercise.

CHANDRA REYNOLDS: Sure. So the current guidelines are about 20 minutes moderate or 10 minutes of vigorous per day. We think that, based on this work and other work, that these levels may not be enough for prolonged sitters. But sitting hasn’t really been in the forefront in terms of guidelines. And so we think this is another aspect by which, when we consider what we do throughout the day, that we might be needing to consider that aspect as well in terms of our health, even at younger ages.

KATHLEEN DAVIS: And just for people who might not be familiar with these guidelines, can you talk about what is moderate physical activity versus extensive physical activity?

RYAN BRUELLMAN: There is a scientific heart rate aspect to it. But really, the best way to think about moderate versus vigorous physical activity would be you’re doing some type of physical activity, and pretend there’s someone next to you. Could you have a conversation with them? Could you say more than a sentence to them?

If you can, then it’s likely going to be low or moderate-level intensity activity. If you’re going along and you can’t say much more than a few words at a time to some individual that would be next to you, you’re doing likely vigorous physical activity.

KATHLEEN DAVIS: So for a lot of us, sitting is a very normal part of the day, right? I mean, I work at a desk all day. Some people have long commutes. If you’re watching TV in the evenings, odds are you’re watching TV while you’re sitting. Chandra, can you remedy long weekdays of sitting with active weekends? Can you potentially cancel some of that out?

CHANDRA REYNOLDS: So we didn’t directly look at that, the weekend warrior type, I guess. And that is something that could be studied. But I mean, certainly trying to get physical activity in your week as best you can is certainly something to aspire to. I don’t know that it would fully erase the effects. And I think, probably coupled with trying to move about the day more than one might otherwise do, so moving away from your desk, taking walks around your space, and ideally, if you work in a space with others, go seek others out for conversations as makes sense, trying to get some more movement during the day and then coupled with additional physical activity, ideally vigorously. And if that’s the weekends, that’s great.

KATHLEEN DAVIS: So we’ve been talking a little bit about developing healthy habits and the importance of developing these habits early. But if someone is listening to this who is older and thinking, oh man, I need to adjust my habits and not sit so much, I know this is outside the scope of this particular study, Ryan, but could a later in life adjustment on habits still potentially have an impact on health?

RYAN BRUELLMAN: I mean, absolutely. I think that while ours is more so focused on younger to more early, early to establish adulthood, this can be translated across individuals as far as just thinking about their sitting behavior in particular. It’s never too late to switch things around, so to speak, and really improve your healthy behaviors, whether that be anywhere from sitting less, doing more exercise, or any of the other major things that are known good things to do for one’s health.

KATHLEEN DAVIS: This is Science Friday from WNYC Studios. If you’re just joining us, I’m talking with my guests about how much sitting is too much sitting. My guests are Dr. Chandra Reynolds and Ryan Bruellman. I have to ask, what are your favorite strategies for breaking up a long day of sitting? I mean, Ryan, do you want to start?

RYAN BRUELLMAN: Sure. I typically will get up and move around if I can. I do have a standing desk now. I do need to practice what I preach since I did write about this and I am studying this. But I’ve also found I do a lot of looking into different data sets and coding and things like that. And I’ve found that if I get into a proverbial block where I can’t figure something out, stepping away and actually doing something, the best thing I’ve found is a run. Going for a 15, 20, 30-minute run really does clear a lot of things, but just really going, walking away, going around and doing something and coming back, it does help with your mindset, but thankfully, too, it helps with your overall physical health.

KATHLEEN DAVIS: What about you, Chandra?

CHANDRA REYNOLDS: Yes, so I do try to move more about the day, especially after the findings of this study. And I do take breaks and may go on a walk to find lunch, for example. And certainly after work, I also take walks with my dog or runs as well. So I do try to break up the day more. And it’s also nice to have social interactions with others than being really focused on Zoom after Zoom meeting. It’s nice to get out.

KATHLEEN DAVIS: So we have seen public health campaigns in the past for things like smoking to warn about the dangers of that. Should there be educational campaigns about the risks of sitting too much? What do you think, Ryan?

RYAN BRUELLMAN: I think that this is a good conversation for individuals to start talking with their doctors or health care professionals. I think that it’s– I mean, I know my doctor will ask me how much physical activity I’m getting, but I can’t remember any time they’ve actually asked me how much do you sit in the average day? So I think it’s important to start having those conversations with one’s doctor, whether it be the doctor bring it up or you bring it up to the doctor and just really start to get it in people’s minds, how much am I sitting throughout the average day?

Is it the majority of the day? Am I sitting the majority of the day at work? Am I sitting the majority of the day when I get home? And then even commuting as well to and from different places. So it’s important to start at least thinking about it. And I think that could be a solid messaging is just to get in individual’s heads and to get into their minds of what their current level is at.

KATHLEEN DAVIS: So we’ve talked a lot about how there are still unanswered questions about a lot of the stuff that we would like to know. Chandra, what would you really love to study in the future now that we have this baseline?

CHANDRA REYNOLDS: Well, I do think that there’s room for evaluating other health outcomes that were examined here and also doing some longitudinal follow-up as well. So for example, our next phase of the life study, we’re looking at both individual self-report and Fitbit measures of both sedentary and physical activity behaviors and health outcomes as well. So I think trying to understand how we also think about our physical activity and how we actually move about the day across a couple of weeks would be very interesting to consider.

KATHLEEN DAVIS: That’s all the time that we have for now. I’d like to thank my guests, Dr. Chandra Reynolds, Professor in the Institute of Behavioral Genetics at the University of Colorado in Boulder, and also Professor emeritus at the University of California, Riverside. And Ryan Bruellman, PhD candidate in genetics, genomics and bioinformatics at the University of California, Riverside. Thank you both so much for being here.

CHANDRA REYNOLDS: Thank you for having us.

RYAN BRUELLMAN: Thank you so much.

KATHLEEN DAVIS: And we want to hear from you. What are your favorite strategies for breaking up a day of sitting? Let us know by going to sciencefriday.com/sit. That’s sciencefriday.com slash S-I-T. We’ll feature some of our favorite suggestions on our website in the coming weeks.

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