By Erika Gebel, PhD
Not so long ago, the sight of a person standing at an office desk, instead of sitting, would have raised eyebrows. Now, there seems to be a legion of dedicated standers, and science may be on their side.
Studies and news stories about the dangers of a sedentary lifestyle have proliferated lately, driving up the sales of exercise balls, standing desks, and, for the truly hard-core, treadmill desks. The evidence that sitting too long increases the risk of obesity, heart disease, and type 2 diabetes continues to accumulate. Plus, it appears that the recommended 30 minutes of exercise, five days a week, doesn’t entirely offset those risks.
While it may seem as if people began to talk about the dangers of physical inactivity only recently, the research dates back to the 1950s, according to David Dunstan, PhD, head of the physical activity laboratory at Baker IDI Heart and Diabetes Institute in Victoria, Australia. Researchers back then compared the health of London bus drivers and conductors. They found that the drivers were worse off, perhaps because they stood less. “If you turn that story the other way,” says Dunstan, “prolonged sitting may [have been] detrimental to their health.”
Americans spend a lot of time sitting. A 2008 study in the American Journal of Epidemiology found that children and adults in the United States spend an average of 55 percent of their waking hours seated, including driving a car, working at a desk, and sitting on the couch. In 2011, Americans over age 15 watched almost three hours of television per day on average, according to the Bureau of Labor Statistics.
While a cause-effect relationship has yet to be proved, a number of studies have found that people who spend many hours sitting are more likely to have health issues. “Slews of studies are coming out that inactivity is a risk” for conditions including heart disease, type 2 diabetes, and dementia, says Yogish Kudva, MBBS, an endocrinologist at the Mayo Clinic in Rochester, Minn. A 2010 study in the American Journal of Epidemiology found that women and men who spent six or more hours sitting per day were 40 and 20 percent more likely to die, respectively, during the 14-year study than those who sat less than three hours a day. The link was strongest for death from heart disease. The increase in death risk was independent of physical activity, so sitting takes a toll even on those people who exercise regularly.
Still, exercise is important, particularly for people with diabetes, because it helps maintain a healthy weight and blood glucose control. “I’m careful not to discount the major benefits of exercise,” says Dunstan, but intense physical activity may not be the only game in town. Plus, exercising doesn’t necessarily translate into less sitting. Marc Hamilton, PhD, of the Pennington Biomedical Research Center in Baton Rouge, La., studied a large group of women between the ages of 45 and 75 and found that “exercisers were not less sedentary.”
Sitting around is linked to the development of type 2 diabetes and worsening blood glucose levels in people with the condition. A 2008 Australian study in the Official Journal of the American College of Sports Medicine of people who were getting the recommended amount of exercise found that the more television they watched, the higher their blood glucose levels and blood pressure were, and the larger their waist circumferences were. The result: an increased risk for type 2 diabetes and heart disease. A 2007 study showed that kids with type 1 who watched more television tended to have higher blood glucose levels.
Sitting may be bad for us simply because it burns so few calories, thus leading to weight gain. Even non-exercise activities—cooking, standing, social dancing, cleaning—all expend more energy than being parked on the couch. Over time, these little movements may help keep the pounds off.
Yet, scientists think that weight is only part of the story. Sitting all day may alter how the body works in harmful ways other than leading to weight gain. Hamilton studies the effects of inactivity on lipoprotein lipase, a human enzyme that gets fat out of the blood and into the muscles for use during activity. He found that inactivity dramatically suppresses the enzyme, leaving fat in the blood. There, the fat can increase the risk of heart disease or be stored in the body. Short bouts of exercise stimulate the enzyme slightly, but this is a small effect compared with the suppression that accompanies long periods of inactivity. That suggests that exercise is not enough to undo the negative health effects of sitting. Frequent low-level activity, such as standing and walking, seems to be the best way to keep lipoprotein lipase in good working order. “Sitting too much is not the same as exercising too little,” says Hamilton.
Take a Break
Technology has made it all too easy for people to spend their lives moving from car seat to office chair, back to car seat, and then to couch. With our jobs and commutes, it may seem impossible to switch to an active lifestyle, even if it’s healthier. Fortunately, research is showing there may be ways to get the benefits of an active lifestyle without spending all day, every day, on our feet.
Dunstan studies whether breaks in sedentary time, even short ones, can help people avoid the ill effects of sitting. In a 2008 study, Dunstan tracked the activity of a group of people who wore accelerometers for a week. He found that, no matter how much total time they spent exercising or sitting, people who had more frequent bouts of activity had slimmer waists and lower blood glucose levels than those who sat for long stretches.
To learn more about mini breaks, Dunstan studied overweight and obese adults in an office environment. Some participants sat all day, while others got up every 20 minutes to walk for two minutes, either strolling or at a moderate pace. Dunstan and colleagues reported in a 2012 article in Diabetes Care that the breaks lowered blood glucose levels after meals, no matter how brisk the walk. “The muscle contraction itself—and not intensity—is the important factor,” says Dunstan.
Now the scientist wants to find “how low you can go” and still derive a benefit. For example, if instead of walking for two minutes, study participants simply stood in place for two minutes, would the blood glucose benefits be the same? What if people took an activity break just once an hour, instead of every 20 minutes? While these questions don’t yet have answers, experts tend to agree that getting on your feet as frequently as you can throughout the day is a break worth taking.