Office workers beware: long periods of sitting at your desk may be a killer. Scientists have identified a new threat from our sedentary lifestyles that they call "muscular inactivity".

Sitting still for long periods of time leads to the build up of substances in the blood that are harmful to health. And exercise alone won’t shift them.

Millions of people lead sedentary lives, spending their days between car, office desk and the couch in front of the TV. While the ill effects are well recognised it has conventionally been thought that they can be offset by frequent trips to the gym, swimming pool or jogging track.

Now researchers say that that is not enough. In addition to regular exercise, office workers need to keep moving while they work, by making regular trips to the printer, coffee machine or to chat with colleagues.

Writing in the British Journal of Sports Medicine, Elin Ekblom-Bak and colleagues from the Swedish School of Sport and Health Sciences and the Karolinska Institute in Stockholm say research shows long periods sitting and lack of “whole body muscular movement” are strongly associated with obesity heart disease, cancer and diabetes, and an overall higher risk of death, irrespective of whether they take moderate or vigorous exercise.

Dr Ekblom-Bak said: “Everyone knows about the health benefits of regular exercise. But what we have not been alerted to before is that long periods sitting down carries an extra risk that cannot be dealt with by taking exercise. There are a growing number of studies that show this.”

“One study compared two groups of sedentary office workers, one of whom had regular breaks to move around while the other remained sitting for up to eight hours a day. The group that had the breaks had better blood lipid levels and blood glucose and less obesity.”

A second study from Australia showed that for every extra hour women spent sitting (watching TV), their risk of metabolic syndrome - a pre-cursor of diabetes and heart disease, rose by a quarter, regardless of how much exercise they took.

Dr Ekblom-Bak said that sitting still should be recognised as a risk to health, independently of taking too little exercise.

“It is important to have a five minute break from desk work every 45 minutes. Don’t email colleagues - walk across the office to give them the message. Take a coffee break or put the printer in the next room. I am a desk worker and I try to do it. It is not difficult but sometimes you get lost in your work and you forget about it.”

The authors say more studies are needed to confirm the ill effects of prolonged sitting and ways of combatting them. But on present evidence they conclude that “keep moving” should be added to the advice to “keep exercising.”

“Climbing the stairs rather than using elevators and escalators, five minutes break during sedentary work,or walking to the store ratner than taking the car will be as important as exercise,” they say.