A new study reveals that prolonged sitting significantly harms even young, active adults, increasing the risk of heart disease and obseity. Researchers also found that current federal exercise guidelines are insufficient to offset the negative effects.

While a great deal of research on aging examines populations in their 60s, this study focused on younger adults. Researchers from UC Riverside and the University of Colorado, Boulder examined health data from over 1,000 men and women in Colorado whose average age was 33. 

Published in the journal PLOS One, the study shows that sitting for 8 or more hours per day increases cholesterol ratios and BMI, even in physically active individuals. Cholesterol ratios, which combine triglyceride and cholesterol levels to gauge heart disease risk, and BMI, a measure of body fat, are early indicators that can predict more severe health issues.

Lengthy sitting sessions can raise even a younger adult’s BMI nearly a full point compared to people who sit only a few hours out of the average day.

“Though unhealthy diet and smoking play a major role in increasing BMI, the full-point jump we saw in the data was just due to sitting alone,” said Ryan Bruellman, lead researcher and doctoral candidate in UCR’s Department of Genetics, Genomics and Bioinformatics.

Similarly, sitting for 8 or more hours a day tended to move men in their early 30s and women in their mid 30s from healthy to higher-risk cholesterol ratios. Because many of the study participants already had cholesterol levels on the high end of optimal, too much sitting made the difference between no and moderate cardiac risk.

While current U.S. Department of Health and Human Services guidelines recommend 2.5 hours of moderate exercise or 1 hour and 15 minutes of vigorous exercise weekly, these levels appeared inadequate for people who sit extensively throughout the day. 

“People don’t often think about how much time they spend sitting, especially in their 20s and 30s, but it matters,” said Bruellman.

Participants self-reported their weekly sitting habits, including time spent sitting at work, during leisure activities, and while traveling. They also detailed their physical activity, categorized as moderate or vigorous. Moderate activities, such as brisk walking, allow for conversation, while vigorous activities, like running, leave participants breathless, according to the researchers. 

Biological markers, such as cholesterol ratios—a key indicator of cardiovascular risk—and BMI, were measured in person.

Importantly, the research findings show that reducing sitting time significantly improves health outcomes. For those unable to limit their sitting time, increasing the intensity and duration of physical activity is crucial. 

Doubling the recommended amount of weekly exercise — either 5 hours of moderate activity or 2.5 hours of vigorous activity — was more effective at lowering health risks associated with prolonged sitting.

The researchers also explored the role of genetics and environment by studying identical twin pairs. This unique approach helped isolate behavioral choices as the key factor in health differences. 

Among twins, those who reduced their sitting time or engaged in higher levels of vigorous activity consistently showed healthier cholesterol ratios and BMIs than their siblings who sat longer or exercised less. 

"This study makes it clear: if you sit for long periods, the standard exercise recommendations are not enough,” Bruellman said. “All adults, even the younger ones, need to move more, and exercise harder, to counteract the impact of sitting.”

While reducing sitting time remains the most effective strategy, the researchers hope to emphasize that all is not lost for individuals with sedentary jobs or lifestyles. Increasing the intensity and duration of exercise—especially vigorous activities—can help offset the damage.

Notably, even 10 minutes of vigorous exercise for every additional hour of sitting significantly mitigated the negative effects of sedentary behavior.

Beyond individual health benefits, the researchers hope the findings help inform future updates to national physical activity guidelines. It is not only the duration but also the intensity of physical activity that makes a difference, particularly for those with predominantly sedentary routines.

“Young adulthood is a critical time to establish healthy habits. If you don’t prioritize movement now, it only gets harder as life fills up with more responsibilities,” Bruellman said.

 “Get up and move—it’s never too early to start.”

(Cover image: Dmitry Ageev/iStock/Getty)