Doing at least an hour of moderately intensive exercise daily — such as brisk walking or cycling — may compensate for the health risks associated with sitting for prolonged periods of time, according to a new meta-analysis published Thursday in The Lancet.

The study’s findings offers both encouraging and disappointing news to people whose jobs require long hours of sitting, perhaps, say, in front of a computer or in the cab of a truck.

Here’s the encouraging news:  Sedentary workers can take a simple action — daily exercise — to lower the increased risk of chronic disease (heart disease, diabetes and some types of cancer) and premature death, which a growing body of research has linked to long stretches of sitting.

And here’s the disappointing news:  To completely undo the risks associated with sedentary behavior, people may need to engage in at least 60 minutes of daily exercise, not the 20-30 minutes most often recommended.

Yet, this study shouldn’t make people who can’t fit a full hour of exercise into their daily routine give up on the idea of being physically active. The study also found that the risk of premature death associated with prolonged sitting was only slightly raised for people who walked, cycled or were otherwise physically active for shorter periods of time (about 25 minutes per day).

“For many people who commute to work and have office-based jobs, there is no way to escape sitting for prolonged periods of time,” said lead author Ulf Ekelund of the Norwegian School of Sports Sciences, in a released statement. “For these people in particular, we cannot stress enough the importance of getting exercise, whether it’s getting out for a walk at lunchtime, going for a run in the morning or cycling to work.”

“An hour of physical activity per day is the ideal, but if this is unmanageable, then at least doing some exercise each day can help reduce the risk,” he added.

Study details

For the study, Ekelund and his colleagues analyzed data collected from more than 1 million people, aged 45 or older, who had participated in 16 studies in the United States, Western Europe and Australia. The researchers asked the original authors of those 16 studies to rework their data so that all of the studies’ participants could be divided into standardized categories of physical activity and sitting time.

The most active group in these studies reported engaging in moderately intensive physical activity for 60 to 75 minutes a day, while the least active group spent less than 5 minutes daily doing that kind of activity.

The data revealed that “among the most active, there was no significant relationship between the amount of sitting and mortality rates, suggesting that high physical activity eliminated the increased risk of prolonged sitting on mortality,” the researchers wrote.

As daily physical activity decreased, however, the risk for premature death increased — even among people who sat for four hours or less per day.

Here are some specific numbers: The people in the 16 studies who sat for eight hours a day were 27 percent more likely to die prematurely than those who sat for four hours a day or less. But if they exercised 30 to 60 minutes per day, that increased risk was only 10 percent to 12 percent.

And if they exercised 60 to 75 minutes daily, the risk disappeared.

“These results provide further evidence on the benefits of physical activity, particularly in societies where increasing numbers of people have to sit for long hours for work,” write Ekelund and his colleagues.

Limitation and implications

The study comes with several important caveats. To begin with, it was an observational study, which means it can’t prove that exercise mediates any health risks associated with prolonged sitting. Also, although the study’s authors adjusted the data for the possibility that the people who were in the lowest activity groups had underlying illnesses that may have prevented them from being physically active, they can’t rule it out as a factor in the study’s final results.

Nor can they completely rule out the possibility that the participants’ socio-economic status might have had an impact on the study’s findings.

Still, the findings are provocative — and potentially important. Health officials estimate that insufficient physical activity is responsible for more than 5 million deaths globally each year. 

“There has been a lot of concern about the health risks associated with today’s more sedentary lifestyle,” said Ekelund. “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.” 

FMI: The study can be read in full (after online registration) on The Lancet’s website. It’s one of a special series of papers on physical activity published in the journal in advance of the Summer Olympic Games, which begins in Rio de Janeiro on Aug. 5.