But for every 30 minutes of sedentary time, the researchers found that the likelihood of death among the study participants increased by about 19 percent.
One limitation of the study, however, is that the accelerometers couldn't distinguish between sedentary time from sitting versus inactive periods when people were standing, the authors note.The study also wasn't a controlled experiment created to prove how or whether sedentary time directly causes premature death.
"The REGARDS study was originally created to examine why blacks (and particularly blacks in the Southern US) have a greater risk for stroke than whites", said Diaz. This new study, however, actually measured sitting time using a hip-mounted accelerometer that tracked movement, and correlated it with the risk of dying during the study period. All-cause mortality was the primary outcome, defined as any death after completion of the accelerometer protocol, regardless of cause.
The results reveal that, on average, participants were inactive for 12.3 hours of a 16 hour waking day, with each period of inactivity lasting an average of 11.4 minutes.
Even though standing desks have become increasingly popular as a possible fix to the problems caused by sedentary time, it's not clear if they help people live longer. The higher average in his own study is likely "due to the fact we studied a middle- and older-aged population", Diaz wrote.
Measuring duration, the researchers clocked participants sitting, on average, for 11.4 minutes at a stretch.
Peter Katzmarzyk, PhD, of Pennington Biomedical Research Center in Baton Rouge, Louisiana, commented that using accelerometry to measure sedentary behavior was a major study strength. Overall then, participants' risk of death grew in tandem with total sitting time and sitting stretch duration - no matter their age, sex, race, body mass index or exercise habits.
What's more, factors such as smoking status and blood pressure were only captured once, and the activity trackers were only worn over one week, meaning that changes in the health or behaviour of participants over time was not taken into account. He also referenced adding sedentary bouts into the analysis, noting that "this study was able to look at how bout duration also is related to mortality, which is a novel analysis".
People with greater total sedentary time were more likely to be black, to smoke, and to have diabetes, hypertension, dyslipidemia, estimated glomerular filtration rate less than 60 mL/min/1.73 m, and atrial fibrillation.
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It's not just about avoiding sedentary behavior or prolonged bouts of sedentary behavior, said Alter, who wrote an accompanying journal editorial. Alter, who did not contribute to Diaz' research, said some scientists theorize that more sitting leads to reductions in insulin sensitivity, while others believe net calorie expenditures decline as sitting increases. We found that those individuals who frequently kept their sitting bouts to less than 30 minutes had a lower risk of death. "You have to move, you have to get up often and break up your sedentary habits if you want to have the lowest risk of death", he explained.
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.
By teasing out these two threads, the findings show excessive sitting is bad and even worse if it is accumulated in lengthy, uninterrupted bouts throughout the day, noted Alter.
Sitting more than 30 minutes at a stretch increases one's chances of dying. "The longer the duration of sitting, the more negative the impact on our cardiovascular health".
Barry A. Franklin, PhD, director of Preventive Cardiology and Cardiac Rehabilitation at William Beaumont Hospital in Royal Oak, Michigan, who was not involved with the study, told MedPage Today that the findings support recent studies which suggest that intermittent low-intensity standing throughout the day may be as important for disease prevention and optimization of health as is structured exercise.
"The first time we do this, the positive effects are immediate", she said.
It is recommended for people who have mainly sedentary jobs to get moving every half hour to help them stay active and promote a healthy heart.
"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".