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Study after study has highlighted the dangers of a sedentary lifestyle that includes extended periods of sitting, and the catchphrase “sitting is the new smoking” has gained traction in the media and in popular consciousness.

Writer Jenny Hall asked the University of Toronto’s Greg Wells how bad sitting really is. Wells is an assistant professor in the Faculty of Kinesiology and Physical Education at �山ǿ�� and an associate scientist in physiology and experimental medicine at the Hospital for Sick Children. His research is focused on developing new ways of treating disease using exercise and nutrition.

We’ve been hearing a lot in the media lately about the health threats of sitting too much. Is sitting actually that bad? Is it really “the new smoking” as we keep hearing?

The physical inactivity epidemic is causing all sorts of health problems. It is associated with almost every chronic disease on the planet, including cancer, cardiovascular disease and type 2 diabetes. The World Health Organization has stated that physical inactivity is one of the leading health concerns for the planet, and that it is closely associated with increased rates of non-communicable diseases. Non-communicable diseases are the leading cause of death on every continent except Africa. If it’s not the world’s number one health concern, it’s pretty close.

Is there any research on how much sitting is too much?

We know a couple things for sure. First, humans need to be vigorously active for at least an hour a day. A very small percentage of our society achieves that. Vigorous activity is something above and beyond just walking. Your heart rate needs to be elevated, and you need to be engaged in something that’s physically demanding for you. An hour of fast walking is an example of vigorous activity.

The other thing we know is that the more physical activity we can incorporate throughout the day, the better. This is because sitting is an independent risk factor. The more you sit, the worse your health is going to be. So in addition to getting the one hour of vigorous physical activity, the more you can intersperse physical activities like walking or moving or getting up to move around throughout the day, the healthier you are going to be.

When you say sitting is an independent risk factor, does that mean that even if you get the hour of vigorous activity a day, you’re still at risk?

Yes. Consider an office worker who’s going to the gym religiously for an hour a day. That’s great. They’ll be way better off than if they never did it at all. The message isn’t don’t do that one hour of exercise – it’s incredibly beneficial. We know that vigorous exercise decreases your risk of breast and colon cancer by up to 50 per cent. But sitting all day is still a problem in and of itself that needs to be addressed.

Are there any guidelines for the other kind of activity you talked about –&�Բ�����;the kind we should try to be interspersing throughout the day?

The best idea is to try to add short bouts of activity throughout the day. I use the 20/20 rule. For every 20 minutes of sitting, stand up and stretch for 20 seconds. Beyond that, within every two-hour block, try to find 15 minutes to do some activity, be it walking or stairs. Even just standing for a while is better than sitting down.

I tell people to stand up in meetings. If everyone else is sitting, find a spot to stand up in the back. If you’re doing a phone call, get up and do it with headphones while you’re standing.

Fifteen minutes of activity every two hours is a tall order if you’re in an office environment.

It is—until you begin to consider the significant damage that sitting causes. The other thing we have learned that’s emerging is the powerful benefit of physical activity for cognitive performance. We now know that physical activity and exercise activate the areas of the brain associated with memory, learning, problem solving and concentration. So an office worker might think they don’t have time to stretch and move, but I would say to them, you can’t afford not to. Not only is your health going to improve, but your performance is going to dramatically improve as well.

So there’s case to be made the physical activity is good for your brain, too?

Absolutely. I watched a documentary on Bob Marley recently. He has a reputation of being this pot smoking guy, but he was a relentless perfectionist. He didn’t let the Wailers play live until they’d practiced for two years. Before they went into recording sessions, he would make everyone play soccer on the beach. They would never go into play unless they had been exercising beforehand. Or, if you read Steve Jobs’s biography, he never did meetings sitting down. His big creative meetings were always done walking.

I think there’s a real sound physiology to these stories, and good rationale for incorporating physical activity into your day. You’re changing the way your brain works. You’re actually flooding the area of the brain that you’re using with oxygen and nutrients. It’s like flipping a switch. The fact that we try to do creative mental work sitting down goes against the way the body and brain are meant to work.

What actually happens in your body when you sit for extended periods of time?

The main thing is decreased blood flow. When you move, you push fluid through all of the tissues in the body. That is one of the main ways the body fights off illness, by pushing fluids through what is called the lymphatic system. You actually have two full circulatory systems in your body—most people don’t know that. You have your blood system that everyone’s aware of, but you also have the lymphatic system. Fluids moving through the lymphatic system are how the body catches viruses and bacteria and other invaders and filters them out and kills them. So the primary way to stay healthy is to get up and move. Beyond decreased circulation, you also get decreased flexibility and decreased nutrients supplied to muscles and the brain.

It sounds like stagnation.

It’s absolutely stagnation. Think about a fresh flowing stream versus water that sits. Sitting water becomes stagnant with low oxygen, and viruses and bacteria grow in it. There’s a similar effect inside the human body.

There do seem to be some parallels to smoking here if you think about sitting as a public health problem. A huge public health push—and some high profile lawsuits—in the latter part of the twentieth century changed cultural ideas about smoking. Does something similar need to happen with sitting?

We need intervention and education at every single level. We need to get physical education back in schools and to make sure that communities are built with sidewalks and parks. We need to make sure that cities get built so that people can ride their bikes. We now know enough that people should know better. I think it’s possible that employers could be held accountable in the future for not providing the opportunity for employees to be as healthy as they could be, given what we now know.

We need a tremendous push on education about the benefits of physical activity and the risks of inactivity.