Survey of 50,000 people across multiple ages, racial, ethnic groups
documents troubling trends
Washington University School of Medicine
Most Americans continue to sit for prolonged periods despite
public health messages that such inactivity increases the risk of obesity,
diabetes, heart disease and certain cancers, according to a major new study led
by researchers at Washington University School of Medicine in St. Louis.
The research team analyzed surveys of 51,000 people from 2001 to
2016 to track sitting trends in front of TVs and computers and the total amount
of time spent sitting on a daily basis.
Unlike other studies that have looked at sedentary behaviors, the research is the first to document sitting in a nationally representative sample of the U.S. population across multiple age groups -- from children to the elderly -- and different racial and ethnic groups.
Unlike other studies that have looked at sedentary behaviors, the research is the first to document sitting in a nationally representative sample of the U.S. population across multiple age groups -- from children to the elderly -- and different racial and ethnic groups.
The research, led by Yin Cao, ScD, an epidemiologist and assistant professor of surgery in the Division of Public Health Sciences, is published April 23 in the Journal of the American Medical Association.
"In almost none of the groups we analyzed are the numbers
going in the right direction," said Cao, the study's senior author.
"We want to raise awareness about this issue on multiple levels -- from
individuals and families to schools, employers and elected officials."
Epidemiologist and co-senior author Graham A. Colditz, MD, DrPH,
the Niess-Gain Professor of Surgery and director of the Division of Public
Health Sciences, said: "We think a lot of these sedentary habits are
formed early, so if we can make changes that help children be more active, it
could pay off in the future, both for children as they grow to adulthood and
for future health-care spending. Sedentary behavior is linked to poor health in
many areas, and if we can reduce that across the board it could have a big
impact."
The new study fills a gap in knowledge on sedentary behavior,
according to the researchers, putting specific numbers on the amount of time
Americans actually spend sitting. For example, the most recent edition of the
Physical Activity Guidelines for Americans, published in 2018 by the Department
of Health and Human Services, recommends less sitting time but offers no
guidance on how much.
The researchers analyzed data from more than 51,000 people who
participated in the National Health and Nutrition Examination Survey between
2001 and 2016, looking at four age groups: children ages 5 to 11 (as reported
by a parent or guardian), adolescents ages 12 to 19, adults ages 20 to 64, and
adults ages 65 and older. Race and ethnicity were defined as non-Hispanic
white, non-Hispanic black, Hispanic and other races, including multiracial.
Total daily sitting time increased among adolescents and adults
from 2007 to 2016, from seven hours per day to just over eight for teenagers,
and from 5.5 hours per day to almost 6.5 for adults, the researchers found.
"Until now, we haven't had data demonstrating the amount of
time most Americans spend sitting watching TV or doing other sedentary
activities," Cao said. "Now that we have a baseline -- on population
level and for different age groups -- we can look at trends over time and see
whether different interventions or public health initiatives are effective in
reducing the time spent sitting and nudging people toward more active
behaviors."
The researchers found that most Americans spend at least two
hours per day sitting and watching television or videos. Among children ages
5-11, 62 percent spent at least that long in front of screens daily.
For adolescents ages 12-19, that number was 59 percent. About 65 percent of adults ages 20 to 64 spent at least two hours watching television per day. And most recently, from 2015 to 2016, 84 percent of adults over age 65 spent at least that much time sitting watching television. And this remained steady over the course of the study.
For adolescents ages 12-19, that number was 59 percent. About 65 percent of adults ages 20 to 64 spent at least two hours watching television per day. And most recently, from 2015 to 2016, 84 percent of adults over age 65 spent at least that much time sitting watching television. And this remained steady over the course of the study.
Across all age groups, 28 percent to 38 percent of those
surveyed spent at least three hours per day watching television or videos, and
13 percent to 23 percent spent four hours or more engaged in watching
television or videos.
Importantly, males of all age groups, non-Hispanic black
individuals of all age groups and participants who reported being obese or
physically inactive were more likely to spend more time sitting to watch
televisions or videos compared to their counterparts.
In addition, computer screen time outside of work and school
increased over this period. At least half of individuals across all age groups
used a computer during leisure time for more than one hour per day in the two
most recent years of the study. And up to a quarter of the U.S. population used
computers outside of work and school for three hours or more.
"How we create public policies or promote social change
that supports less sitting is unclear and likely to be complicated,"
Colditz said. "If a neighborhood in a disadvantaged community is unsafe, for example, parents can't just send their kids outside to play. Our environments -- the way our cities, our school days and working days are designed -- play roles in this behavior that are difficult to change. But at least now, we have a baseline from which to measure whether specific changes are having an impact."
Colditz said. "If a neighborhood in a disadvantaged community is unsafe, for example, parents can't just send their kids outside to play. Our environments -- the way our cities, our school days and working days are designed -- play roles in this behavior that are difficult to change. But at least now, we have a baseline from which to measure whether specific changes are having an impact."
Chao Cao, a recent graduate of the Brown School and a data
analyst in Yin Cao's lab, co-led the analyses.
Washington University also collaborated with researchers at a number of other institutions, including Charles Matthews, PhD, at the National Cancer Institute (NCI); Lin Yang, PhD, at the Alberta Health Services, Calgary, Canada; the Harvard T.H. Chan School of Public Health; Memorial Sloan Kettering Cancer Center; and Massachusetts General Hospital and Harvard Medical School.
Washington University also collaborated with researchers at a number of other institutions, including Charles Matthews, PhD, at the National Cancer Institute (NCI); Lin Yang, PhD, at the Alberta Health Services, Calgary, Canada; the Harvard T.H. Chan School of Public Health; Memorial Sloan Kettering Cancer Center; and Massachusetts General Hospital and Harvard Medical School.
This work was supported by grants from the National Institutes
of Health (NIH), grant numbers P30CA008748 and P30CA091842.