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.
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.
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."
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.
This work was supported by grants from the National Institutes of Health (NIH), grant numbers P30CA008748 and P30CA091842.
Yang L, Cao C, Kantor ED, Nguyen LH, Zheng X, Park Y, Giovannucci EL, Matthews CE, Colditz GA, Cao Y. Trends in sedentary behavior among the U.S. population, 2001-2016. Journal of the American Medical Association. April 23, 2019.
Washington University School of Medicine's 1,500 faculty physicians also are the medical staff of Barnes-Jewish and St. Louis Children's hospitals. The School of Medicine is a leader in medical research, teaching and patient care, ranking among the top 10 medical schools in the nation by U.S. News & World Report. Through its affiliations with Barnes-Jewish and St. Louis Children's hospitals, the School of Medicine is linked to BJC HealthCare.