Scientists in Ottawa are monitoring how blood pressure and oxygen consumption change as children sit and watch TV. ((CBC))

The bodies of even the most physically active Canadians take a physiological hit from sitting for hours, say scientists who warn about health effects of an increasingly sedentary society and prescribe some standing advice.

Canadian researchers are part of a pioneer field of study looking at the effects that sitting has on the body. At a lab in Ottawa, scientists are observing children as they watch TV, monitoring their pressure and oxygen consumption. The scientists want to see how sedentary time, such as sitting all day at school and then channel surfing at night, harms children's health.

After two to seven hours of uninterrupted sitting, there is evidence "that is enough to increase [subjects'] blood sugar, to decrease their good cholesterol and to have a real impact on their health," said Travis Saunders, a researcher in exercise physiology at the Children's Hospital of Eastern Ontario Research Institute in Ottawa. 

Conventionally, sitting and lying down were seen as simply the opposite of moving. But our cells and muscles actually respond to the strains of prolonged sitting, said Mark Tremblay, director of the Healthy Active Living and Obesity Research Group at CHEO.

"There are certain physiologic mechanisms that come into play way down at the sedentary side that don't factor in on the exercise side and vice versa," Tremblay said. "So there appears to be different mechanisms at play."

There are likely important physiological activities that go on while we sit that need to be studied separately from exercise physiology, he said.

Early evidence suggests spending long periods sitting affects the entire body, from the way it metabolizes fat and sugars to how the brain functions, and raises osteoporosis risk through lower bone density.

Sedentary health effects — preliminary research

A 2003 study showed each two-hour-per-day increase in TV viewing time was associated with a 23 per cent increase in obesity after taking other lifestyle factors like diet into account.

Each two-hour-per-day increase in sitting at work was linked with a 5 per cent increased risk of obesity.

Women who spent seven hours or more per day sitting had an increased risk of endometrial cancer compared to those who sit less than three hours per day.

In 2008, Spanish researchers found the odds of having a mental disorder were 31 per cent higher for subjects who spent more than 42 hours a week watching TV than for those who watched fewer than 10.5 hours a week.

It is possible to mitigate the damage with simple steps such as standing up regularly. The body "responds to very small interruptions in that sitting," Tremblay said. "And this is where the promise might be."

Since our muscles don't know the difference between contracting from lifting a barbell or books off a desk, adding exercise during the workday could help, researchers say.

People are trying walking treadmill desks, standing workstations, walking meetings and sitting on exercise balls instead of chairs, and using computer prompts to remind themselves to build those interruptions into the workday.

Children's author Gillian Chan of Dundas, Ont., has a specially designed treadmill built into her desk so she can walk while she writes.

"The first week I found it quite tiring, but after that, I found it almost energizing," Chan said. "I felt much more alert."

Even someone who walks briskly or jogs for 30 minutes each day has 15.5 waking hours of sedentary time, researchers say, and this down time is expected to increase for most people.