(CNN) There's a key culprit in the battle against sitting. Time spent watching TV and videos has remained consistently high in the United States over the past 15 years, but time sitting at a computer has increased dramatically, new research finds.

Leisure-time computer use increased between 4.8% and 38% for various age groups between 2001 and 2016, said Yin Cao, senior author of the new study and an assistant professor of surgery at Washington University School of Medicine in St. Louis.

Overall, up to 43% of the US population used a computer for two or more hours a day and up to 25% used a computer for three or more hours each day in 2016.

The result of these increases: Teens spent about 8.2 hours a day sitting while adults sat for 6.4 hours a day.

Both groups saw a one-hour increase over the decade ending in 2016, Cao said.

Cao believes that her research , published Tuesday in JAMA, will help Americans better understand our sedentary habits -- and change them.

Sitting trends over the past 15 years

"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," Cao said.

For the first time, the US Department of Health and Human Services mentioned in last year's edition of its physical activity guidelines "that people would benefit from both increasing moderate to vigorous activity and also reducing time spent sitting," she said.

She wondered: How much do Americans sit, and how has the trend changed over the past 15 years? To answer these questions, Cao and her co-authors used data from the National Health and Nutrition Examination Survey on 51,896 people -- 10,359 children, 9,639 teens and 31,898 adults -- from 2001 through 2016.

Overall, up to 65% of the population reported watching TV for at least two hours each day, the study found. "This is quite high and has been overall stable over the past 15 years," Cao said. Computer time, though, has been increasing over that same period.

Just 43% of children reported using a computer for one hour per day or more in 2001; that rate increased to 56% in 2016, the study indicates. The estimated prevalence for teens increased from 53% to 57%, and for adults it went from 29% to 50% between 2003 and 2016. Only adults and teens reported their total sitting time.

"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," Cao said.

Every little bit helps

Peter Katzmarzyk , a professor at Louisiana State University's Pennington Biomedical Research Center and a member and fellow of the American College of Sports Medicine, said the study's value is in showing trends over time.

Katzmarzyk, who was not involved in the research, noted that the paper also highlights some important differences across demographic groups that could result in health disparities. "For example, levels of sitting were higher in males, in African Americans and also in adolescents and adults with overweight or obesity," he said.

Although everyone needs to focus on increasing activity and reducing sitting, "it is even more important to limit the time spent sitting in people who are not meeting the physical activity guidelines, because they are at highest risk" for chronic diseases and premature mortality, he said.

A separate study published this week in the Journal of the American College of Cardiology found that moderate-to-vigorous physical activity offset the link between sitting time and increased risk of death from all causes and cardiovascular disease death risk. The study tracked nearly 150,000 people ages 45 and older.

Keith Diaz , an assistant professor of behavioral medicine in the Columbia University Department of Medicine, said that the message of the research published in JAMA may be familiar but that it is important.

"Largely, we're becoming more sedentary as a nation, and one of the principal contributors to that rise in sedentary time is our computer usage," said Diaz, who did not participate in the research.

"What I was really struck by was, 62% of children are watching TV for two or more hours per day," he said. "And they're using computers a lot, too."

A parent, he added, "these behaviors 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."

He said people who have read his research often ask him two questions: "What should I do when I take a break from my sitting time?" and "When I take that break, how long does that break have to be?"

His most recent study found that intensity matters but is not essential.

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"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%," he said. Replace 30 minutes of sitting with more vigorous activity, and you lower your risk by 35%.

He also found that "short bursts of activity, if you get enough of them across the day, will be enough to lower your risk from sitting all day."

"To combat sitting doesn't require you going to the gym and working out for hours at a time," he said.

Getting off your office chair or the couch and taking a short break here or there is enough, he said: "It doesn't have to be complicated. It doesn't have to be hard. It doesn't have to be long."