People in the study who took the most breaks from sitting - up to 1,258 short breaks in one week - were about two pant sizes smaller than those who took the fewest, as few as 99 breaks in one week, said study researcher Genevieve Healy, who studies population health at the University of Queensland in Australia.
And a smaller waistline means less abdominal fat and better heart health, Healy said.
"A high waist circumference is associated with an increased risk for type 2 diabetes, high blood pressure and cardiovascular disease," she told MyHealthNewsDaily.
When we stand, the large muscles in our legs and the back are continually contracting to maintain our posture, but when we sit or recline, these muscle groups are basically inactive, Healy said.
"So even short breaks from sitting get these large muscle groups contracting," she said.
The study will be published tomorrow (Jan. 12) in the European Heart Journal.
Healy and her colleagues studied 4,757 people, ages 20 and older, who participated in the U.S. National Health and Nutrition Examination Survey. All participants wore an accelerometer on their right hips for seven days during their waking hours.
These accelerometers measured the amount and intensity of the participants' physical activity every minute. When activity levels were very low, the researchers assumed the participants were sedentary, Healy said.
Participants ranged from 1.8 hours of sedentary time a day to 21.2 hours a day, according to the study. The average length of a break from sitting was 4.12 minutes.
Researchers found that even among those who spent a long time sitting, those who took a lot of breaks had smaller waistlines and lower levels of C-reactive protein - an indicator of inflammation in the body - than those who didn't take breaks.
The 25 percent of people who took the most breaks from sitting had waistlines that were, on average, 1.61 inches (4.1 centimeters) smaller than the 25 percent of people who took the fewest breaks, according to the study.
Increasing evidence shows sitting is bad for us
The finding comes on the heels of a study published earlier this week in the Journal of the American College of Cardiology, which found that spending more than four hours of your leisure time in front of your computer or TV a day can increase the risk of being hospitalized for, or dying from, heart disease.
And a 2009 study of 5,453 people published in the journal Obesity showed that a 1-centimeter increase in waist circumference is associated with an increased chance of premature death.
Researchers have been "following the relationship between markers of sedentary behavior, such as TV watching and screen time, but now we have started to objectively quantify physical inactivity as well as activity," said Jeanne D. Johnston, an assistant professor of kinesiology at Indiana University who was not involved with the new study.
Because the study relied on results from the accelerometers, instead of self-reported information from participants, the results "provide a foundation" for exploring why periods of long sitting are bad for health, Johnston told MyHealthNewsDaily.
For example, researchers could now further explore the way insulin levels are affected by movement, and therefore lack of movement, she said. Being consistently active may increase insulin sensitivity, whereas inactivity can lead to insulin resistance, a precursor to type 2 diabetes.
Inflammation in the body in response to physical activity or high-fat meals might be another a culprit, Johnston said.
Pass it on: Taking short breaks from sitting is associated with a slimmer waistline and better heart health.