A new study published in the Journal of the American College of Cardiology has found that prolonged sedentary behavior — spending hours sitting, reclining, or lying down — significantly increases the risk of heart failure and cardiovascular death. Even those who meet exercise guidelines aren’t fully shielded from these dangers.

Don’t sit for more than 10 hr a day

If you’re reading this, the odds are you spend too much time sitting down. Modern life encourages sitting—whether it’s working at your desk, driving in your car, or just chilling on the couch. This is nothing new, we’ve known that extended periods of sitting down are bad for you. Some studies have suggested that having an active lifestyle can counteract the damage but according to the new research, it doesn’t counteract all the damage.

Using data from nearly 90,000 participants in the UK Biobank study, researchers assessed daily activity levels using wrist-worn accelerometers. Participants were tracked for an average of eight years, during which sedentary behavior was closely linked to increased risks of heart-related conditions, including atrial fibrillation (AF), myocardial infarction (MI), heart failure (HF), and cardiovascular (CV) mortality.

The average sedentary time was 9.4 hours per day, and just one extra hour sharply escalates the risks.

The tipping point seems to be at 10.6 hours a day. For those in the top quartile of sedentary time, the risk of heart failure jumped by 45%, and the risk of cardiovascular death soared by 62%. These figures persisted even among individuals meeting the widely recommended 150 minutes of moderate-to-vigorous physical activity (MVPA) per week.

“Our findings support cutting back on sedentary time to reduce cardiovascular risk, with 10.6 hours a day marking a potentially key threshold tied to higher heart failure and cardiovascular mortality,” said Shaan Khurshid, MD, MPH, a cardiologist at the Massachusetts General Hospital and co-senior author of the study. “Too much sitting or lying down can be harmful for heart health, even for those who are active.”

How to reduce your risk

It’s not entirely clear why sitting down for so long is bad for you, although researchers have some theories (for instance, sitting reduces blood flow and negatively impacts insulin sensitivity). However, the causality between sitting down and negative health effects is so well established that we’d be wise to think about ways to reduce our sedentary sitting periods.

“This study adds to the growing evidence of a strong link between sedentary behavior and cardiovascular health,” said Harlan M. Krumholz, MD, SM, Harold H. Hines Jr. Professor at Yale School of Medicine and Editor-in-Chief of JACC. “The findings strongly suggest that we need to get people moving to promote better health.”

Exercise is, of course, one of the most powerful tools for maintaining heart health, and it’s the first thing you should look at. Current guidelines emphasize at least 150 minutes of moderate-to-vigorous physical activity weekly to lower cardiovascular risk. Yet, as Dr. Khurshid pointed out, that only accounts for a small slice of the day.

Other than sitting down less, researchers found that even complementing the vigorous activity with lighter workouts can make a big difference. Replacing just 30 minutes of sedentary time with physical activity, even light movement, significantly reduced risks. For example:

• Replacing 30 min sedentary time with moderate-to-vigorous activity leads to:
  • 15% lower risk of heart failure
  • 10% lower risk of cardiovascular mortality
• Substituting light activity for 30 min sedentary time leads to:
  • 6% lower risk of heart failure
  • 9% lower risk of cardiovascular mortality

Accelerometers were important in this study

To assess the participants’ activity, researchers used wrist accelerometers: wearable devices that measure movement and inactivity, providing precise data on physical activity levels. Accelerometers worn on the wrist are imperfect at detecting posture but they are still much better than self-reporting.

These small, wearable devices measure movement in multiple directions, providing objective, minute-by-minute data about activity levels. Compared to traditional methods like self-reporting, accelerometers offer way better accuracy and reliability. The researchers found that participants substantially overestimate their exercise and underestimate their sedentary behavior. Although imperfect, these accelerometers still provide a much better perspective of how much people actually move.

The widespread adoption of accelerometers opens new doors for truly understanding and addressing public health challenges. These devices could be used in larger, more diverse populations, providing real-world insights into daily activity patterns. As technology advances, accelerometers may also integrate with other tools, like heart rate monitors or posture sensors, for an even more comprehensive view of health behaviors.

Taking steps towards a healthier life (literally)

The message is clear: sitting too much harms your heart. But the good news is that the risks can be reduced. Here are some simple strategies to help you cut back on sedentary time:

• Set timers to remind yourself to stand or stretch every 30 minutes.
• Incorporate walking meetings or phone calls into your workday.
• Use active transportation like biking or walking for short trips.
• Replace screen time with light chores, gardening, or hobbies that involve movement.

Your heart is the engine that keeps your body running, and every small step you take can strengthen it. Whether it’s swapping 30 minutes of screen time for a brisk walk, standing during phone calls, or simply stretching between tasks, these small changes can ripple into big benefits for your health.

The science is clear: movement matters, not just in the gym but throughout your day.

The study “Accelerometer-Measured Sedentary Behavior and Risk of Future Cardiovascular Disease” was published in the Journal of the American College of Cardiology.