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. It is one of a special series of papers on physical activity to coincide with the forthcoming Olympic Games.
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 25 to 25 minutes per day, which is the amount often recommended in public health guidelines) attenuated 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," they add.
Data From More Than a Million People
This is the first meta-analysis to use a harmonized approach to directly compare mortality between people with different levels of sitting time and physical activity, the researchers comment. They included 16 studies, with data on 1,005,791 individuals (aged >45 years) from the United States, Western Europe, and Australia.
The team confirmed the finding that prolonged sitting is associated with an increase in all-cause mortality. About 75% of these deaths were due to cardiovascular disease and cancer (breast, colon, and colorectal), Dr Ekelund commented.
As well as considering how long individuals sat each day, the researchers also divided the study participants into four equal-sized groups, depending on the amount of physical activity they reported. The least active group reported being active for less than 5 minutes per day, the next group was active for 25 to 35 min/day, the next group for 50 to 65 min/day, and the most active group for 60 to 75 min/day.
"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.
"A clear dose-response association was observed, with an almost curvilinear augmented risk for all-cause mortality with increased sitting time in combination with lower levels of activity," the researchers comment.
These most active individuals were used as the referent group for the analysis (hazard ratio of 1).
At highest risk were individuals who reported the least amount of physical activity, even if they did not spend a long time sitting each day. For the group that was least active (less than 5 min/day) but also spent the least time sitting (less than 4 h/day), the hazard ratio for premature death was 1.27.
This was significantly higher (P < .0001) than for individuals who were the most active (60 to 75 minutes of physical activity each day) but who also reported the longest periods of sitting (>8 h/day), who had a hazard ratio for premature death of 1.04.
This hazard ratio was not significantly different from the referent group, which led to the main conclusion that 1 hour of activity can offset 8 hours of sitting.
The researchers emphasized that the findings suggest that physical activity is particularly important, no matter how many hours a day are spent sitting.
Speaking to reporters at a Lancet press briefing in London, Dr Ekelund said that the biological mechanisms behind these findings are unclear, but work in animal studies suggests that inactivity is linked to a decreased production of certain hormones.
He also emphasized 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.
Asked by Medscape Medical News if he practices what he preaches, Dr Ekelund, who is tall and lean, laughed and said yes, that he is in the high activity group. He is a keen cross-country skier and does about 5 to 7 hours of exercise each week.
The authors have disclosed no relevant financial relationships.
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Cite this: One Hour of Activity Offsets Risks From 8 Hours of Sitting - Medscape - Jul 27, 2016.