A new study has shown that with the advent of computers and screens, Americans are sitting more than they did before. There are several studies in the past that show the association between sitting for prolonged periods and bad health.
The study co-authored by cancer epidemiologist Yin Cao from Washington University in St. Louis says that there is inadequate data on the number of hours Americans spend sitting in front of their computers, but the numbers are alarming. The results of the study titled, “Trends in Sedentary Behavior Among the US Population, 2001-2016,” were published in the latest issue of the Journal of American Medical Association.
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The team looked at the amount of time Americans spend in sedentary ways such as sitting or lying down from the National Health Nutrition Examination Survey. The survey included a total of 51,896 participants including 10,359 children, 9,639 teens and 31,898 adults followed up between 2001 and 2016. They noted that between 2007 and 2016 the number of hours spent sitting rose from 6.4 hours per day to 8.2 hours per day among adults as well as teenagers. Between 2001 and 2016 people were spending their time sitting in front of the television or screens for leisure for at least 2 hours per day. With time the number of leisure hours spent in front of the computer screen rose. In 2003 around 29 percent adults spent at least an hour in front of the computer relaxing and this rose to around 50 percent in 2016. The numbers were 53 and 57 percent respectively for teenagers. In 2016 around 43 percent and 25 percent American adults use the computer sitting down for two or more hours per day and three or more hours per day respectively, finds the study.
Cao said in a statement, “[People] work indoors more than ever before and this may also change their leisure time activity as well.” She added that most people did not know how bad sitting for prolonged periods was for their health. She said that there have been no steps to address this problem of sitting for too long in schools and work places.
Experts add that switching to standing desks may not be a solution as standing is not an exercise. They recommend getting up and walking around for a bit after around 15 minutes of sitting. Cao said, “Research evidence has been growing on the association between sedentary behavior -- primarily TV watching -- and a variety of diseases, including obesity, cardiovascular disease, cancer, Type 2 diabetes and overall mortality.” The US Department of Health and Human Services in its last year’s recommendations says, “people would benefit from both increasing moderate to vigorous activity and also reducing time spent sitting,” explained Cao. She added, “Hopefully, this paper will be helpful in terms of setting the national achievable goal of reducing sitting, given that we already know prolonged sitting is bad for many health outcomes.”
Harm caused by sitting could be offset by a little exercise
A similar study by Ken Diaz from the Center for Behavioral Cardiovascular Health, Department of Medicine, Columbia University Irving Medical Center, New York, also look at the effects of replacing sedentary activity with bouts of physical activity on risk of death. The study titled “Potential Effects on Mortality of Replacing Sedentary Time With Short Sedentary Bouts or Physical Activity: A National Cohort Study,” was published in the March 2019 issue of American Journal of Epidemiology.
The team replaced total sedentary time with either “light-intensity or moderate to vigorous physical activity (LIPA or MVPA)” or replaced long periods of sedentary activities like sitting with shorter periods of sedentary time. They also assessed the association of these changes with long term mortality risk.
The study involved 7,999 participants over the age of 45 years enrolled in the Reasons for Geographic and Racial Differences in Stroke (REGARDS) study. Between 2009 and 2013, accelerometry technique was used to measure sedentary time. Results showed that both light-intensity or moderate to vigorous physical activity or LIPA and MVPA could offset the mortality risk of long hours of sitting. Same was not true for replacing long periods of sitting with shorter periods of sedentary activities. Authors concluded, “These findings suggest short sedentary bouts still carry mortality risk and are not a healthful alternative to prolonged sedentary bouts. Instead, physical activity of any intensity is needed to mitigate the mortality risks incurred by sedentary time.”
Diaz says about the JAMA research, “What I was really struck by was, 62% of children are watching TV for two or more hours per day. And they're using computers a lot, too.” He, being a parent, could identify. He said, “...these behaviours really manifest early on, in childhood, and it's probably something we have to start curtailing and targeting really early if we are going to break this vicious cycle of us becoming a more sedentary society.”
His recommendation is that no physical activity is trivial enough to replace sedentary time. He said, “So if you were to replace 30 minutes of sedentary time with 30 minutes of light activity -- a casual stroll down the hall -- you would lower your risk of early death by 17%.” Same way replacing half an hour of sitting with moderately vigorous activity can lower risk of early death by 35 percent he said. He added that there is no need to visit the gym each day for a workout. Short bouts of activity across the day could be enough to lower the harm caused by sitting around all day. He signed off, “It doesn't have to be complicated. It doesn't have to be hard. It doesn't have to be long.”
According to Peter T. Katzmarzyk of the Pennington Biomedical Research Center in Baton Rouge, Louisiana, who was not part of either of the two studies, “We’ve just got to really work on the population to get the message out there. Physical activity is good for everyone.”
Just 20 minutes of exercise needed!
In another recent and related study published in the Journal of the American College of Cardiology, researchers looked at the effects of sitting on risk of deaths. They also found that this risk could be mitigated by routine moderate-to-vigorous physical activity or MVPA.
Lead author of the study, Emmanuel Stamatakis said in a statement, “In our study, sitting time was associated consistently with both overall premature mortality and cardiovascular disease mortality in the least physically active groups – those doing under 150 minutes of moderate to vigorous intensity physical activity per week.”
For this study the team followed 149,077 Australian men and women aged over 45 for around 9 years. They looked at the amount of time the participants spent sitting, standing, sleeping or engaged in MVPA. Based on activity they divided the population into four groups –
- less than four hours
- four to less than six hours
- between six and eight hours
- more than eight hours
Physical activity again was divided into five categories –
- “inactive” (no physical activity)
- “insufficiently active” (between one and 149 minutes)
- “sufficiently active” (150 to 299 minutes)
- “sufficiently active” (300 to 419 minutes) and
- “highly active” (420 minutes or more)
Stamatakis says, “Meeting the Australian public health recommendation of 150 to 300 minutes per week – equivalent to around 20-40 minutes per day on average – appeared to eliminate sitting risks... Any movement is good for health but physical activity of moderate to vigorous intensity – that is activities that get people out of breath– is the most potent and most time-efficient.”
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