People who sit for one to two hours at a time may have a higher risk of early death than those who sit cumulatively as long, but in shorter bouts, a study has warned. The study found that it is not just the amount of time spent sitting, but also the way in which sitting time is accumulated during the day, that can affect risk of early death. Researchers found that adults who sit for one to two hours at a time without moving have a higher mortality rate than adults who accrue the same amount of sedentary time in shorter bouts. "We tend to think of sedentary behaviour as just the sheer volume of how much we sit around each day," said Keith Diaz, associate research scientist at Columbia University Medical Center (CUMC) in the US. "But previous studies have suggested that sedentary patterns - whether an individual accrues sedentary time through several short stretches or fewer long stretches of time - may have an impact on health," said Diaz, lead investigator of the study published in the journal Annals of Internal Medicine. The researchers used hip-mounted activity monitors to objectively measure inactivity during waking time over a period of seven days in 7,985 black and white adults over age 45. On average, sedentary behaviour accounted for 77 per cent of the participants' waking hours, equivalent to more than 12 hours per day. Over a median follow-up period of four years, 340 of the participants died.
Mortality risk was calculated for those with various amounts of total sedentary time and various sedentary patterns. Those with the greatest amount of sedentary time - more than 13 hours per day - and who frequently had sedentary bouts of at least 60 to 90 consecutive minutes had a nearly two-fold increase in death risk compared with those who had the least total sedentary time and the shortest sedentary bouts. The researchers also found that participants who kept most of their sitting bouts to less than 30 minutes had the lowest risk of death. "So if you have a job or lifestyle where you have to sit for prolonged periods of time, we suggest taking a movement break every half hour. This one behaviour change could reduce your risk of death, although we do not yet know precisely how much activity is optimal," Diaz said. The study was the largest to link objectively measured sedentary time and sedentary patterns with mortality risk, researchers said.
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