People should not only exercise more but also sit less. (Canadian Press)Chances are, you're reading this on some type of screen, whether it's a computer monitor, cellphone, smartphone or other device. Researchers are increasingly finding that all that time spent sitting, working and playing online can take its toll on our bodies, both physically and mentally.

More and more content is being delivered to us via screens, from live streams and downloadable video to Facebook pages and Twitter feeds. That means a lot more time exercising our fingers and eyes but not much else.

Shawn Roche, 24, of Ottawa, says he's addicted to online gaming and discussion boards. For Roche, it's the competitive and social aspects of pushing his gaming skills to the limit that attract him to spend more than 40 hours a week online.

"When cut off from the internet, I typically find something else to do," Roche said — by email, of course.

"I still routinely get outside and go mountain biking, as well as practice martial arts on and off, but it certainly feels like a substantial change of pace."

The gaming keeps him mentally stimulated, Roche said, but he also tends to feel physically tired when online. All that time sitting around just doesn't seem to suit his athletic nature.

Sedentary lifestyle

In 2002, the World Health Organization listed inactivity, or sedentary lifestyle, as one of the 10 leading global causes of death and disability.

A sedentary lifestyle includes sitting, reading, watching television and using a computer for much of the day with little or no vigorous exercise. As expected, the lifestyle contributes to obesity and cardiovascular disease.

In 2007, the U.S. Surgeon General also raised alarm about the importance of physical activity for health, saying it reduces the risk of premature death, coronary heart disease, hypertension, colon cancer and Type 2 diabetes.

The report recommended that adults get 30 minutes or more of moderate-intensity physical activity on all or most days of the week to maintain weight and improve health.

Walking briskly or gardening count as moderate-intensity aerobic exercise. The rule of thumb is that it should be strenuous enough that you are able to talk but not sing during moderate activities.

Reduce sitting and screen time

In Canada, a May 2009 study of 17,000 men and women suggested only five per cent of Canadian adults compensate for the time they sit at work through exercise.

The longer people spend sitting, the more likely they are to die prematurely, regardless of their fitness levels, Claude Bouchard, a retired professor from Quebec City who is now executive director at the Pennington Biomedical Research Center in Baton Rouge, La., and his colleagues found.

Even among fit Canadians, the risk of premature death escalated depending on the amount of sedentary time in their day.

The mortality risk was 1.54 times higher among those who spent almost all of the day sitting compared with those who spent almost no time sitting, the team reported.

Given those findings, the researchers suggested that doctors counsel patients to not only increase their level of physical activity and maintain a normal body weight but to also reduce the amount of time they spend being sedentary in general and sitting in particular.

Blood clots, disturbed metabolism

A report by Statistics Canada also suggested that "screen time" — the number of hours a day spent watching television or sitting in front of a computer — should be considered a distinct contributing factor to obesity, in addition to physical inactivity and diet.

Why is the time we spend sitting so important to our health?

One reason is that excessive sitting can lead to blood clots, like those that afflict some airline passengers.

Deep-vein thrombosis, or DVT, is thought to be caused by sitting rigidly for too long. A blood clot forms in leg veins and travels to the lungs or heart or brain days or weeks later, where it can lead to a heart attack or stroke.

Enzymes in the blood vessels of muscles responsible for burning fat also get shut off within hours of not moving.

Laboratory studies suggest that time spent sitting is linked to major disturbances in how the body metabolizes fuels such as glucose and lipids, Bouchard noted.

Taking breaks from sitting helps to normalize this process, he said.

Walking at work is something Bouchard and others at his lab do regularly.

The same goes for Dr. Doug Bradley, director of the University of Toronto's Centre for Sleep Medicine and Circadian Biology. Outside Bradley's office at the Toronto General Hospital, there's a 100-metre long corridor.

"Knowing what I know, I get up every hour, and I walk up and down that corridor," Bradley said. "If I'm sitting here at my desk, I'm going to be retaining fluid in my legs. Even if I can't see it, it's happening."

Walking contracts the muscles in the calves, which pumps fluid out of the legs to prevent fluid retention.

'Absolutely extraordinary' finding

In February 2009, Bradley and his colleagues published their discovery that the amount of fluid moving out of the legs at night also was a very strong predicator of how severe sleep apnea was in 23 men who were not obese.

In obstructive sleep apnea, a person's airway is partially or completely blocked during sleep, leading to a lack of oxygen and frequent waking. The condition is associated with an increased risk of death from heart disease or stroke.

'I'm certainly not going to do anybody any harm by telling them to get up and walk a couple hundred metres every hour during the day.'— Dr. Doug Bradley

"What we found was absolutely extraordinary," Bradley said.

"Almost certainly what we're seeing happening is, the more time they spent sitting in the daytime, the more fluid accumulated in their legs. And when they went to sleep at night, that fluid came back to haunt them when it moved into their necks. So, this is a completely new concept of what sleep apnea is caused by."

The effect was so powerful that it was a two to three times better predictor of sleep apnea than known risk factors like obesity, neck size and abdominal fat, he said.

The finding opens the door to potentially new ways of treating sleep apnea other than relying on uncomfortable masks that pump air through a person's nose or nose and mouth to keep the airway open at night.

The combination of obstructive sleep apnea and heart failure, both of which have fluid retention as a defining feature, is a particularly toxic mixture.

Like a clogged sink

In a person with heart failure, the heart can't pump enough blood. The blood backs up into the lungs and into the legs, causing shortness of breath and difficulty walking.

If the individual also has untreated sleep apnea, his or her risk of sudden death from the heart stopping or beating irregularly increases, researchers have found.

"[It's] just a vicious cycle," Bradley said.

(CBC) In heart failure, the pressure inside the heart goes up, like a clogged drain pipe in a sink. The fluid back ups, first to the lungs and then into legs.

When these people go to bed at night, the fluid comes back into their lungs and neck, contributing to sleep apnea.

The sleep apnea causes them to stop breathing at night, reducing oxygen levels, raising blood pressure and causing the heart to become even more stressed, making the heart failure worse, Bradley explained.

He is now leading a trial in 40 centres and eight countries to find out whether treating sleep apnea in people with heart failure will help them survive longer.

As well, Bradley's team is investigating whether preventing fluid retention or preventing fluid from moving from the legs to the neck at night will prevent sleep apnea.

Ideally, exercise would be the best way to deal with the problem. But getting sedentary people to get moving takes time. So, the team is testing the fluid-retention principle by prescribing diuretic pills that cause urination, although the drugs can have some side-effects, including dizziness, and require frequent trips to the bathroom.

Other potential approaches to preventing fluid retention in the legs include wearing support stockings during the day and raising the head of the bed so fluid doesn't move into the neck at night.

In the meantime, Bradley advises his patients who show signs of fluid retention to walk more.

"I don't know exactly how much exercise you need to do, but I suspect it's not a whole heck of a lot," Bradley said. "I'm certainly not going to do anybody any harm by telling them to get up and walk a couple hundred metres every hour during the day."

As of 2004-05, data are the results of a fusion of Mark II and PPM data. This has inflated per capita viewing over previous years. Source: BBM, Nielsen Media Research, Statistics Canada