Study: Prolonged Sitting Damages Health

Taking a break to walk every 20 minutes instead of staying seated for hours helps reduce the body's levels of glucose and insulin after eating, according to a study — the latest to highlight the hazards of long periods of inactivity. Though the results, published in the journal Diabetes Care, don't show whether these reductions have any lasting health benefits, experiencing large glucose and insulin spikes after a meal is tied to a greater risk of heart disease and diabetes. "When we sit our muscles are in a state of disuse and they're not contracting and helping our body to regulate many of the body's metabolic processes," said David Dunstan, a professor at Baker IDI Heart and Diabetes Institute in Melbourne, Australia. Dunstan and his colleagues have reported previously that people who watch more than four hours of TV a day are likely to have an earlier death. With this study, they experimented with how prolonged sitting could affect responses to food. After a meal, glucose levels in the blood go up, followed by a rise in insulin, which helps cells use blood sugar for energy or store it. Then, levels in the bloodstream start to go down. In people with Type 2 diabetes, this process falls out of whack usually because the body no longer responds to insulin properly. After a meal, blood sugar and insulin levels spike and remain high. Dunstan's group looked at 19 overweight adults who didn't exercise much, asking them to come into a laboratory and sit for seven hours while having their blood sugar and insulin levels sampled hourly. After the first two hours, they drank a 763-calorie drink high in sugar and fat, then sat for another five hours. Each person went through three days of experiments, with each day separated by a week or two. On one day, they sat the entire time, only taking breaks to use the bathroom. On another, they broke up the sitting session and took a two-minute break to walk around every 20 minutes following the drink — and on another day, they took similar breaks, but with more vigorous activity. The days when people sat without interruption resulted in a spike in blood sugar within an hour of the drink from about 90 milligrams per deciliter (mg/dl) to about 144 mg/dl. On days when they got up every 20 minutes, blood sugar rose from 90 mg/dl to only about 125 mg/dl. Overall, getting up and engaging in light activity reduced the total rise in glucose by an average of 24 percent, compared to the group that kept sitting. That difference was almost 30 percent with moderate-intensity activity. The results were similar for insulin. Levels peaked about two hours after the drink, but they rose higher when the people continued sitting compared with moving about. "What's shocking to me in these studies is not how good breaks are but how bad sitting is," said Barry Braun, a professor at the University of Massachusetts in Amherst, who was not involved in the study. He said a good rule of thumb is to try and get up about every 15 minutes, even if it's just to walk around the room. What's not clear is whether the 30 percent reduction in glucose and insulin levels will translate into health benefits. "This was only studied over one day. The next question is, can that reduction be (achieved regularly) and translate to reductions in atherosclerosis?" said Dunstan, whose group is now working on a longer experiment.