Can sitting really kill you? Maybe not if you get enough exercise.

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We need to sit less, but doing lots of exercise might help offset the harmful impacts of sitting, says a leading Australian expert.

The view that large amounts of exercise might be protective against the health risks of sitting comes from Australian sitting researcher Dr David Dunstan, following the release of a new British study that suggested sitting was not as bad for our health as once thought.

We have been told for several years now that ‘sitting is the new smoking‘, after a host of studies showed clear links between sitting time and increased risk of premature death.

Worse still, we were told being active at other times of the day did not offset sitting’s harms. So going for a run or to the gym after work would not make up for the damage to your body from spending the bulk of your day sitting at your desk.

When we sit, our leg and trunk muscles are inactive and this can lead to a potentially-harmful build-up of sugars and fats in our blood.

However, the new British study of more than 5,000 British public servants followed for 16 years, challenged previous research that suggested sitting caused harm.

The participants in the study reported weekly on how long they sat in a number of situations, including at work, while watching TV, during leisure time and during non-television leisure time. But the researchers could find no correlation between sitting time and an increased risk of dying, after controlling for factors including diet and general health.

Dr Dunstan, head of physical activity at Baker IDI Heart and Diabetes Institute in Melbourne, questioned the new findings, suggesting that the British results may stem from limitations in the study’s design.

There is now a substantial body of evidence-based research suggesting sitting is harmful, he said.

“It’s [still] a case of getting more physical activity into our lives and sitting less,” he said.

The British researchers admit one potential weakness in their study is it looked only at links between sitting and dying early.

It did not look for an increased risk of diseases that may not necessarily cause death. Other studies have shown sitting is linked with diabetes, heart disease and some cancers.

Dr Dunstan also believes much larger numbers of people might need to be followed to give a true picture of the harms of sittings.

He said all previous evidence – including one Australian study of 220,000 people – consistently showed people who sat a lot had an increased risk of dying from all causes, compared to those who did not sit much.

Exercise may be key.

The fact the British participants were unusually active might have protected their health too, Dr Dunstan said.

It is another point the authors concede, stating that the London-based employees were far likelier to stand (on buses and trains) or walk during their commute to work. Indeed on average, the group in the British study walked nearly 43 minutes a day, double the reported UK average.

We have been told in the past daily exercise was not enough to undo sitting’s effect on our health.

Dr Dunstan said this was because studies showed people who sat a lot had an increased risk of dying from all causes compared to those who did not sit much, even after accounting for differences in physical activity between the groups.

However, some researchers recently started to look more closely at the effects of different exercise levels and found “hints” that 300 minutes a week of moderate intensity exercise might be enough to offset some of sitting’s harms, he said. Moderate intensity exercise is when your heart and breathing rate are increased but you can still talk in full sentences.

The British study appears to support this idea. One of its authors, Dr Melvyn Hillsdon of the University of Exeter, said the team’s work “overturns current thinking on the health risks of sitting and indicates that the problem lies in the absence of movement rather than the time spent sitting itself”.

“The trouble is there’s not a lot of people in the population up at that level [of exercise],” Dr Dunstan said.

“If you’re very active, could your sitting time be irrelevant? We don’t know yet. But when you think about our population, the proportion of people who would be in that high activity level would be very low.”

Advice to break up your sitting time, either by walking around or standing (which still uses more muscles than sitting), is part of Australia’s National Physical Activity Guidelines.

And in June this year, UK guidelines were released recommending desk-based office workers spend at least two hours of their working day standing or moving, and to gradually progress to four hours.

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