Sitting – no matter where, no matter when – could be your new worst enemy. With everyone from scientists to your employer repeating it, get comfy: its days may well be numbered.

It's been a long time coming. Since the 1700s, being sedentary has been linked with ill health. In the 1950s, researchers in London focused on the heart health of bus drivers compared with bus conductors. Perhaps unsurprisingly, those whose jobs didn't involve sitting for eight hours had a far lower risk of heart problems. What the research did not isolate, says Leon Straker, professor in the School of Physiotherapy and Exercise Science at Curtin University, was whether it was the activity that was good or the sitting that was bad. Now, after a half a century or so of research on the positive benefits of activity, a groundswell of scientific evidence suggests that our bus drivers were at a double disadvantage. It is now clear that sitting, which 76 per cent of us do for more than six hours a day, is a health risk, irrefutably linked with heart disease, diabetes and obesity.

Australia is a research leader in the field. Papers by scientists at the University of Queensland since 2000 showed that some markers for cardiovascular metabolic health (blood pressure, blood sugar and blood fat levels) were predicted by how much time was spent sitting, regardless of how much time was spent active. In 2012, a University of Sydney study using 45 and Up data from over 220,000 Australians showed that people who sit for 11 hours or more a day are 40 per cent more likely to die within three years than those who sit for less than four hours. The risk of colon cancer doubles and that of heart disease is increased by 50 per cent – even if exercise is performed regularly. Last year, standing  was shown by the same team to lower mortality risk.

"Humans' systems have evolved for being active. If their systems are inactive for a long period of time, they go into a state that doesn't appear to be healthy," says Straker. "It is a major problem, it's a bit of a stealth problem," he says of the chair as a health danger.

As well as the unholy triumvirate of heart disease, diabetes and obesity, effects also include back and skeletal pain and possibly blood clots. But what is it about sitting, in particular, that can have such dramatic effects on otherwise fit individuals?

Three theories dominate the world of inactivity physiology, says the man responsible for the "hour of TV knocks 22 minutes from your life" revelation, Tim Olds, a health sciences professor at the University of South Australia.

First, we're using less energy, so we're getting fatter. (The Mayo Clinic's James Levine has shown that stand up work burns through double the calories of seated work.)

Second, it's not sitting per se, it's what you do when you're sitting that matters. Watching television, for example, is often accompanied by staying up late and eating junk food. "TV," says Olds, "is the killer."

Third is Dr Marc Hamilton's findings that during periods of long sitting, more fat enters the bloodstream because of a sharp drop in the enzyme that is responsible for storing fat in fat cells. At the same time our glucose levels increase and we begin to develop a resistance to insulin. (Data for this study was collected in Baton Rouge, Louisiana, which has no pavements, muses Olds. "We had to get a taxi to cross a road," he remembers of the city that is in the grip of a major obesity epidemic.)

With the largest portion of our sedentary time spent at work, offices are an obvious place to chip away at what was once seen as an innocuous, even necessary habit. The key is to break up sitting time with moments of gentle activity – a walk to the water fountain or delivering a message to a colleague in person rather than by email, every 30 minutes, appears to be enough, Straker says.

Better yet, place a computer above a treadmill or exercise bike. It won't be long, he believes, before computer jobs no longer mean a fixed, seated position. As voice and gesture technology improves, we will have no need to be anchored to one spot, at the mercy of desk chairs. For now, though, as is the wont of responsible (and litigation-savvy) employers, standing and height-adjustable desks are on the rise, from the Prime Minister's office to Fairfax's Pyrmont HQ.

It's a trend that hasn't gone unchecked by the Human Factors and Ergonomic Society of Australia, which is working on a position paper in response to the threat to chairs.

"Sitting is not the new smoking, sitting is perfectly OK," says society member Stephen Hehir. "The best thing is not to be sitting the whole time, the dynamic nature of work is more important than just standing or just sitting."

Using a raised desk may increase the risk of varicose veins, deep-vein thrombosis and plantar fasciitis, making a variety of postures paramount, he says.

The matter is, of course, not without its contrarians and opportunists. After all, barely a decade ago, we were all being given ergonomically designed office chairs in a bid to combat back problems.

If there's one thing we know for certain and, indeed, have known for hundreds of years, it's sit less, move more. And, for those who will yield to the standing desk but aren't prepared to give up vegetating in front of the telly, Olds has another snippet that may be worth holding dear: for every hour of exercise, you add 90 minutes to your life, meaning that your 22-minute TV debit could be balanced by a 15-minute jog.