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PHILADELPHIA (CNN) — You’ve heard it before, but the message is still urgent: One in four U.S. adults sits for more than eight hours a day, according to a new study from the U.S. Centers for Disease Control and Prevention. Four in 10 adults do not exercise to either a vigorous or even moderate degree each week, the analysis also reveals.

Add to that, one in every 10 Americans reports both behaviors — sitting for more than eight hours a day and being physically inactive — according to the study, published Tuesday in the medical journal JAMA.

“Both high sedentary behavior and physical inactivity have negative health effects,” the authors of the study said. “And evidence suggests that the risk of premature mortality is particularly elevated when they occur together.”

The CDC researchers used data from the most recent 2015-16 National Health and Nutrition Examination Survey of about 5,900 adults as the basis for their analysis. This survey is unique in that it combines both interviews and physical examinations of all the participants.

Nearly 26 percent of the surveyed adults reported sitting for more than eight hours per day, while nearly 45 percent said they were inactive. The researchers discovered similar patterns for both women and men.

When you combine the two behaviors, the greatest proportion of adults — nearly 14 percent — fell into the group that reported sitting for six to eight hours each day and not getting enough exercise. Another 11% said they sit for more than eight hours per day while being inactive; the same percentage said they sit for four to less than six hours per day while being inactive.

The healthiest group is also the smallest, the researchers say. Just under 3 percent of the adults who participated in the survey said they sit for less than four hours per day and are sufficiently active.

Overall, sitting for more than eight hours per day combined with too little activity increased with age, according to the survey results.

A 2017 study found that no matter how much you exercise, sitting for excessively long periods of time is a risk factor for early death from any cause. That study was based on nearly 8,000 adults.

“Sit less, move more” is what the American Heart Association encourages all of us to do. But this simplistic guideline doesn’t quite cut it, said Keith Diaz, lead author of the 2017 study and an assistant professor of behavioral medicine at Columbia University Department of Medicine.

“This would be like telling someone to just ‘exercise’ without telling them how,” Diaz said.

Exercise guidelines from the CDC recommend that adults do moderate-intensity aerobic exercise for two hours and 30 minutes every week, plus muscle strengthening activities on two or more days a week.

Though Diaz believes that a similar recommendation is needed for sitting, his 2017 study did not provide enough evidence to construct a hard and fast rule, he said: More research is needed.

In the meantime, he has a suggestion for a possible sitting guideline.

“We think a more specific guideline could read something like, ‘For every 30 consecutive minutes of sitting, stand up and move/walk for five minutes at brisk pace to reduce the health risks from sitting,’ ” he said.

(The-CNN-Wire™ & © 2018 Cable News Network, Inc., a Time Warner Company. All rights reserved.)