We all know inactivity plays a key role and we have all heard by now of the dangers of too much sitting, but for those of us with sedentary jobs, there is now good news — an hour of moderate-intensity activity offsets the health risks of 8 hours of sitting.

That conclusion comes from a meta-analysis of trials involving more than 1 million individuals, reported online July 27 in The Lancet. This is the second time the journal has published such a series. The main message 4 years ago was that physical inactivity is a killer — leading to 5.3 million premature deaths annually worldwide, which is as many as caused by smoking and twice as many as associated with obesity. The finding prompted public health campaigns warning that "Sitting is the New Smoking" and that "Prolonged Sitting is Killing You."

The new message is that "it is possible to reduce — or even eliminate — these risks if we are active enough, even without taking up sports or going to the gym," says lead author of the meta-analysis, Ulf Ekelund, PhD, from the Norwegian School of Sports Sciences in Oslo and Cambridge University, United Kingdom.

The study found that the health risks of sitting for 8 hours a day can be offset by 1 hour of moderate-intensity activity, which includes brisk walking (at 5.6 km/h) or cycling for pleasure (at 16 km/h). About a quarter of all individuals in the study reported this level of physical activity.

 But even shorter periods of activity (about 20 to 25 minutes per day, which is the amount often recommended in public health guidelines) decreased the mortality risks associated with prolonged sitting, the researchers found.

 "For many people who commute to work and have office-based jobs, there is no way to escape sitting for prolonged periods of time," Dr Ekelund said in a statement. "For those people in particular, we cannot stress enough the importance of getting exercise, whether it's going for a walk at lunchtime, going for a run in the morning or cycling to work. An hour of physical activity is the ideal, but if this is unmanageable, then at least doing some exercise each day can reduce the risk," he said.

 The world needs to get serious about physical activity," the Lancet editors write in an accompanying editorial. The study by Ekelund and colleagues shows "how regular activity can diminish the increased mortality risk of prolonged sitting and should help shift the current focus on reducing sitting times alone to more emphasis on regular activity”.

 "Among the most active, there was no significant relation between the amount of sitting and mortality rates, suggesting that high physical activity eliminated the increased risk of prolonged sitting on mortality," the researchers note.

 But as the amount of physical activity decreased, the risk for premature death increased.

 The researchers emphasised that the findings suggest that physical activity is particularly important, no matter how many hours a day are spent sitting.

 He emphasised the message about "moving more," suggesting that people should walk as much as they can and that if they do need to sit for prolonged periods, they should break up those periods with short bursts of activity, such as walking for 5 minutes every hour.