Researchers worked with a very small sample. They measured nine girls between 7 and 10 years old for blood flow in their legs before and after they spent three hours in beanbag chairs in the lab watching movies and playing games on iPads. They also measured changes in circulation after a similar three-hour period except that the children got up and exercised for 10 minutes every hour.
The researchers found that the veg-out sessions were associated with a 33% decrease in the flexibility of the artery in the thigh, similar to the effect that marathon sitting has been observed to have in adults. In contrast, there was no difference in vessel flexibility after the sessions that were interrupted by bouts of exercise.
"We didn't expect quite such a profound effect in children," partly because children seem like they could be more resilient to sedentary behavior, said Alison McManus, associate professor of pediatric physiology at the University of British Columbia. McManus is lead author of the study, which was published in the journal Experimental Physiology
on September 15.
The stiffening of the thigh artery in this study could increase the risk of cardiovascular problems by about 25%, at least until the vessel regains its flexibility, McManus said. However, the artery did seem to bounce back quickly; the blood flow was normal again by the time the girls returned to the lab several days later for the exercise session.
The concern is that if children make a habit of being inactive, their arteries could eventually lose the stretchiness, and they will be at greater risk of heart attack and stroke when they are adults, McManus said.
Ample research in adults has suggested that being glued to a chair or couch for hours on end could increase levels of blood sugar and cholesterol
, and risk of obesity, heart disease and even premature death. The current study is one of the first to look at physical effects of sedentary behavior in kids.
Another surprise of the study is that the young girls were able to sit still for so long. During the three-hour session, they only spent about eight minutes standing or moving their legs, based on sensors attached to their legs, and that was mostly to readjust their position. "We always have this idea that kids fidget (but) they are very good at sitting still," McManus said. To their detriment, the study suggests.
Although it is hard to know how much more sedentary kids are now than in the past — this behavior was not really measured 10 or 15 years ago — it could be a lot, McManus said. Children today spend about 60% of their waking hours inactive.
Even though the current study only involved girls, boys would probably also be affected in the same way by sitting for long periods, said Alan Hedge, professor of ergonomics at Cornell University, who was not involved in the study.
Likewise, although the beanbag chairs in the current study are probably among the worst seats in terms of cutting off circulation, even the most ergonomic chairs would probably do the same damage, although it might take a longer sitting session, Hedge said.
"This research suggests that children are not that different from adults in terms of fundamental physiology of the body," Hedge said. "It confirms that sitting compresses blood vessels in young people just as much as it does in adults [and] just as much as it does in elderly."
There could even be benefit for children in standing or moving 10 minutes every half hour, which Hedge advises, even though those in the current study only moved for 10 minutes every hour. This additional movement could help them remain more alert, and maintain good bone and muscle health, Hedge said.
Teachers and schools can help by designing lessons and schedules around getting children to stand up every half hour or hour, and parents should keep an eye on their children to make sure they don't spend too much time parked in front of the TV or computer, Hedge said.