Taking a break to walk around every 20 minutes, instead of staying seated for hours on end, helps reduce the body's levels of glucose and insulin after eating, according to a new study.
While the latest results don't show whether these reductions have any lasting health benefits, experiencing large glucose and insulin spikes following a meal is tied to a greater risk of heart disease and diabetes.
"What's shocking to me with 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 research.
The new study, published in the journal Diabetes Care, is the latest to highlight the hazards of spending long periods being physically passive, whether it's zoning out in front of a TV or working behind a computer screen.
Glucose levels go up after meals
David Dunstan, a professor at Baker IDI Heart and Diabetes Institute in Melbourne, Australia, 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. They didn't prove that sitting was to blame for the shorter lives, so to explore what sitting actually does to the body; Dunstan's group this time 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 body cells use that blood sugar for energy or store it, so 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.
Minimise glucose and insulin response
"What we have at the present is consensus ... that we should be looking at ways to minimise that exaggerated response (of insulin and glucose) after meals," said Dunstan.
His group took 19 overweight adults who didn't exercise much and asked 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, the participants drank a 763 kilojoules drink high in sugar and fat, and then sat for another five hours.
Each person went through three days of experiments, each day spaced out by a week or two. On one day, they sat the entire time, reading, watching TV or working on a computer, only taking breaks to use the bathroom.
Light activity reduces rise in glucose
On another day they broke up the sitting session and took a two-minute break to leisurely walk around every twenty 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 people were able to get up every 20 minutes, blood sugar rose from 90 mg/dl to only about 126 mg/dl.
Overall, getting up and engaging in light activity reduced the total rise in glucose by an average of 24%, compared to the group that kept sitting. That difference was almost 30% with moderate-intensity activity.
Metabolic benefits from not sitting
The results were similar for insulin – levels peaked about two hours after the drink, but they rose higher when the people continued sitting than when they moved about.
"Their results are exactly what I would have hoped to see and what I would have expected to see," said Alpa Patel, a researcher at the American Cancer Society.
She said experiments in animals have also shown that taking breaks from sitting can have "a considerable amount of metabolic benefits."
Braun said he was surprised that the breaks involving more intense exercise showed nearly the same benefits as the breaks to walk around.
Still, he thinks it's pretty clear how just getting up would help lower glucose and insulin.
Muscles not used when sitting
"We know muscle contractions help take up glucose into the muscle," Braun said. Less glucose translates into less insulin.
"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," Dunstan said.
What's not clear is whether the 30% reduction in glucose and insulin levels seen in this study will actually translate into health benefits.
"This was only studied over one day," said Dunstan. "The next question is, can that reduction be achieved regularly and translate to reductions in atherosclerosis?"
Dunstan's group is working on a longer, three-day sitting experiment.
Sitting has detrimental effects
Braun said a good rule of thumb is to try to get up about every 15 minutes, even if it's just to walk around the room.
The Centres for Disease Control and Prevention recommend that most adults get 150 minutes of moderate exercise each week.
Patel said that sitting can still have detrimental effects on people who exercise if they're the "active couch potato" type – taking time to work out, but still spending hours and hours a day sitting.
"Break up sitting time wherever and whenever possible," she said.
(Kerry Grens, Reuters Health, March 2012)