Sitting 8 hours a day? An hour a day of physical activity could offset the health risks

Office workers and others who sit for eight hours a day can avoid the health risks associated with that inactivity by doing an hour of physical activity a day, a new study suggests.

The research team behind the study wanted to know if it was possible for people who sit all day at an office job to compensate for the harmful effects of that lack of activity by getting some exercise. In short, the answer is yes.

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Researchers arrived at their findings by analyzing data from 16 studies involving more than a million people. They found that people who were physically active, but sat for eight hours a day, had a much lower risk of death compared to people who weren't physically active, even if they sat for fewer hours.

"This suggests that physical activity is particularly important, no matter how many hours a day are spent sitting," the study's authors said.

The researchers found that doing at least one hour a day of physical activity a day was enough to completely offset the increased risk of death from doing all that sitting.

By physical activity, researchers said walking at 5.6 km/h meets the standard, as would cycling at 16 km/h.

"Our message is a positive one: it is possible to reduce — or even eliminate — these risks if we are active enough, even without having to take up sports or go to the gym," said lead author Ulf Ekelung, a professor at the Norwegian School of Sports Sciences and the University of Cambridge.

That message was welcome news for Toronto lawyer Kiran Gill, who often bikes to and from work. "I am surprised it only takes one hour to mitigate the effects of eight hours of sitting. I would think that would take a lot more," she told CBC News.

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While an hour a day of physical activity is ideal, researchers said getting less than an hour of daily exercise can still reduce the health risks of sitting for hours. 

The key message from the study is that if long periods of sitting each day can't be avoided, it's crucial to be physically active.

Heavy TV viewing 

Researchers also looked at the health risks of one particular type of sedentary activity — watching a lot of television.

They found that those who sat and watched at least three hours of TV per day had an increased risk of death for all groups, except those who engaged in moderately intensive physical activity for 60 to 75 minutes per day.

But for those watched at least five hours of TV per day, even high levels of physical activity were not enough to eliminate higher mortality risks.

Why does TV watching for hours at a time seem to be more unhealthy than a similar amount of time sitting at a desk?

Researchers suggest that watching a lot of TV may be a marker of a more unhealthy lifestyle in general. They also suggest that because people tend to watch TV in the evenings after dinner, it may affect their metabolism. People also tend to snack while watching TV.

The study was published Wednesday in The Lancet.