The last year has seen a flurry of research that shows long periods of sitting are a risk factor for cardiovascular disease, type 2 diabetes, and some types of cancer. Last week, scientists went through that research in search of an answer to a major question: Is sitting a health risk even for people who exercise?
There’s good news and bad news, according to the meta-analysis conducted by Aviroop Biswas and Dr. David Alter at the Institute for Clinical Evaluative Sciences in Toronto and published in the Annals of Internal Medicine.
The bad news is that sitting for prolonged periods of time — something all of us do — increases the risk of death from heart disease, type 2 diabetes, and certain kinds of cancer even in people who exercise regularly. Those who sit a lot have a 15 to 20 percent greater risk of dying from these diseases than those who don’t, the researchers found.
But there’s some good news, too. Though exercisers didn’t get a free pass to sit between workouts, they were able to offset some of the risks associated with sedentary behavior.
People who sat a lot and didn’t exercise regularly saw nearly a 40 percent jump in their mortality risk, the meta-analysis found. People who exercised saw just a 5 to 10 percent bump. (Blending the two groups together gets the 15 to 20 percent overall figure.)
Until recently, researchers thought that sedentary time was just another way of measuring exercise, or lack there of. If someone sat a lot, that meant that they didn’t exercise. But contemporary adult life is almost entirely geared toward sitting, so even those who exercise a lot still sit at work, when driving, at the movies and so on.
Researchers have come to see that how much a person exercises and how much a person sits are two distinct, although overlapping, risk factors.
“It’s the first time we’ve really quantitatively opened up the hood and looked at the engine, and there’s two parts of the engine. We don’t yet know if we tune up one part if that’s enough,” said Alter.
What researchers don’t yet know is exactly how sitting drives up health risks. It’s not simply body fat. Many of the studies used in the new analysis adjusted for body mass index (BMI), a measurement of body fat.
The meta-analysis showed that obese people had more additional risk than those with an optimal BMI, Alter said. However, even those with the leanest rear ends saw their risks go up as a result of sitting on them.
Sitting Less in a Seated Society
In an editorial published alongside the meta-analysis, Neville Owen, Ph.D., a pioneer in the field of sitting research at the Baker IDI Heart and Diabetes Institute in Melbourne, Australia, and Brigid Lynch, Ph.D., of the Cancer Council Victoria in Melbourne, point out how life-changing the findings could be.
“Society is engineered, physically and socially, to be sitting-centric. In our workplaces, homes, common methods of transportation, and recreational venues, we are required or encouraged to sit,” they wrote.
Public health organizations will have to devise guidelines for how much sitting people can safely do if further research supports these early findings.
“If we’re going to recommend that medically, we want to have some methodology to make that recommendation,” said Dr. Andrew Bremer, a program director at the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), which is part of the National Institutes of Health.
The NIDDK is funding studies to look at the biology that drives the connection between sitting and lifestyle diseases.
“We know activity can promote how the body utilizes the nutrients it’s going to take in. When you use your muscles at a low-to-moderate or a moderate-to-high capacity, is there a dose for that? Do you have to do it for a half hour, or is there a legacy effect? These are all questions that people are starting to ask in a scientific fashion,” Bremer said.
The institute is also interested in studies that focus on specific things people can do to stay healthy without giving up their jobs. Is taking a trip to the water cooler every hour enough, or should we be doing jumping jacks every half-hour?
What Can You Do to Stay Healthy at Work?
Concrete guidelines may not come for some time, but the evidence that sitting is bad for us is strong enough for people to try to take action now.
“All we can really say is, ‘Try to sit less,’ but we can’t really say 2 hours a day or 6 hours a day is safe,” said Peter Katzmarzyk, Ph.D., a pediatric obesity and diabetes expert at Louisiana State University and the author of one of the 47 studies included in Biswas and Alter’s analysis.
The experts don’t think people should feel powerless. Given how much time most of us sit, there’s plenty of room for improvement.
Almost no one, even serious athletes, sits for less than four hours a day, the lowest-risk recommendation, Alter said.
Alter has his cardiology patients write down how much time they spend sitting still. Pedometers and fitness apps can help, but a pen and paper will do, too. Then, they’re tasked with cutting that time by one hour.
The most obvious way to sit less is to switch to a standing desk at work. Standing burns about 140 calories per hour, as opposed to 70 at rest. But standing desks don’t work for everybody, since they can put additional strain on the lower back and legs, Alter said. And not all workplaces will accommodate them.
Sitting less also almost certainly includes doing more exercise, whether it’s in short bursts during the workday or in longer stints at the gym.
“Even if you sit all day, you’ll get benefits from physical activity. And even if you do physical activity, you’ll get risks from sitting the other 23 hours a day,” Katzmarzyk said.
“It’s kind of like exposure to the sun — we don’t say, ‘Just do it for 10 minutes,’ we say, ‘Limit it, use sunscreen,’” he said. “Try to get up as much as you can. It’s the same concept.”