You’re in relatively good shape. You even exercise on a regular basis. You don’t have to worry if you sit at your desk all day, right? Wrong. All that time sitting in front of your computer can be a killer — literally.
It’s common knowledge that sedentary people are at increased risk for such serious health problems as obesity, heart disease, stroke, type 2 diabetes, depression, and some cancers. But even healthy people who exercise may still be at risk, if they spend too much time sitting. In fact, long periods of sitting can actually negate all of your hard work.
“We’re literally not built to sit all day long. That’s not the bio-design of the human being,” said James Levine, PhD, director of the Mayo Clinic/Arizona State University Obesity Solutions Initiative, and author of the new book “Get Up! Why Your Chair is Killing You and What You Can Do About It.” He likens excess sitting to idling your car all day long. “No one switches on a car and lets it idle for 13 hours a day. So why would you do that to your body?”
Levine said he “was actually quite discouraged” to learn that sitting undermines the benefits of working out. “If you think about people with regular jobs, it’s quite an achievement to get to a gym at the end of the work day.”
But the mounting evidence about the negative effects of prolonged sitting “does not conflict with the data that going to the gym benefits your health in a dose–respondent fashion; namely, the more you go, the more benefit you get,” Levine said. Yet exercising for an hour at the end of a day doesn’t necessarily offset the harm you’ve done to yourself during the other 13 hours of the day, he says.
So why is sitting so bad for us? Prolonged sitting causes a drop in lipoprotein lipase, an enzyme that removes fat from your blood to be used for fuel, research has shown. Without sufficient levels of lipoprotein lipase, triglycerides (bad cholesterol) soar and HDL (good cholesterol) drops. In addition, all that sitting causes blood to pool in your legs, which in turn reduces blood flow to your heart, increasing your risk for developing cardiovascular problems such as deep vein thrombosis.
Now for the good news. You can reverse the harmful effects of sitting by simply getting up and moving for about 5 minutes every hour, according to one study. Researchers measured blood flow and arterial function in the legs of subjects who on one day sat for 3 hours without moving and on another day walked for 5 minutes once every hour.
“When people sat for 3 hours at a stretch, they had a decrease of blood flow in the legs,” said Saurabh Thosar, PhD, lead author of the study, now a postdoctoral researcher with the Oregon Institute of Occupational Health Sciences in Portland. However, on the day the subjects walked for 5 minutes every hour, even at a speed of only 2 miles per hour, they did not have arterial impairment and did not have a decrease in blood flow.
Not only does breaking up sitting time help maintain vascular function in your legs, but movement — getting your muscles to contract and blood to flow — also helps counter the effects of gravity.
“When you’re sitting, your legs are lower than your heart, and it requires effort on the part of leg muscles and vessels to pump blood back to the heart. So it’s also a gravity-dependent phenomenon,” Thosar said. Bottom line: “Don’t sit for long periods of time. If you do have to sit for long periods of time, make sure you take breaks every hour. If you’re not able to take breaks every hour maybe do some leg exercises while sitting.”
Like Levine, Thosar also cautions that movement to break up periods of sitting doesn’t take the place of substantive exercise. The benefits of exercise are different from the benefits of short bursts of activity.
“This is not meant to be a substitute for exercise,” Thosar said, “but if you are not going to be able to exercise at all you should at least break your sitting time. If you don’t exercise and you sit for a long time, then you are at greater risk.”
You can start minimizing your risk by standing up and moving at regular intervals. When you get up after sitting for a long time, you change how your body handles its fuels.
“As soon as you walk, you double your metabolic rate above resting,” Levine said. “Even at 1 mile an hour, walking is a very powerful way of burning calories and activating your metabolism.”
Fortunately, finding ways to break up your sitting routine doesn’t require a lot of planning or even any equipment.
“It doesn’t really take that much exercise to prevent this dysfunction,” Thosar said. If people engage in even light activity — simply moving around in some way, not necessarily exercising — there is a benefit. The American College of Sports Medicine offers many suggestions for finding ways to work more activity into your daily routine:
Other options include taking the stairs when possible, instead of the elevator, or parking a little farther away from work. But Levine cautions against becoming too reliant on “tips and tricks” to get moving.
“There’s a big difference between tips and tricks and plans,” he said. You may have little choice about your desk job. Maybe you can’t stand and move around at work. If you walk into almost any office, you’ll see people working at computers, in cubicles, who don’t have a choice about sitting; you generally can’t carry your computer around with you. However, anyone can commit to a regular 15-minute walk after lunch or schedule walking meetings whenever possible, says Levine, inventor of the first treadmill desk.
“In other words, there are things that are within our power to plan, and there are things that are outside our power of influence to plan,” Levine said. “It is incumbent upon us to plan things that we can actually do, but to make it a proper plan because this is a big issue. The world is engineered to sit . . . and that needs to change.”
March 03, 2015
Christopher Nystuen, MD, MBA