Sitting down for too long is dangerous, even if you lead an active life

A new study published in Journal of the American College of Cardiology found that prolonged sedentary behavior—spending hours on end sitting, slouching, or lying down—significantly increases the risk of heart failure and cardiovascular death. Even those who meet the exercise guidelines are not completely protected from these dangers.

Do not sit for more than 10 hours a day

If you’re reading this, chances are you spend too long time sitting down. Modern life encourages sitting, whether you’re working at a desk, driving a car or just relaxing on the sofa. It’s nothing new, we know that prolonged periods of sitting are bad for you. Some studies have suggested that living an active lifestyle can reverse the damage, but according to new research, it doesn’t reverse all the damage.

Using data from nearly 90,000 participants in UK Biobank study, researchers assessed daily activity levels using wrist-worn accelerometers. Participants were followed for an average of eight years, during which time sedentary behavior was strongly 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 suddenly increases the risks.

The peak appears to be 10.6 hours per day. For those in the top quartile of sedentary time, the risk of heart failure increased by 45%, and the risk of cardiovascular death increased by 62%. These numbers persisted even among people meeting the widely recommended 150 minutes of moderate to vigorous physical activity (MVPA) per week.

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

How to reduce your risk

It’s not entirely clear why sitting down so much is bad for you, although researchers have a few theories (for example, sitting reduces blood flow and has a negative impact on insulin sensitivity). However, the causality between sitting down and negative health effects is so well established that it would be wise to think about ways to reduce our periods of inactivity.

“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 per week to reduce cardiovascular risk. However, as pointed out by Dr. Khurshid, this is only a small part of the day.

Aside from sitting less, researchers have found that even supplementing 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 the risks. For example:

• Replacing 30 minutes of sedentary time with moderate to vigorous activity leads to:
  • 15% lower risk of heart failure
  • 10% lower risk of cardiovascular mortality
• Replacing light activity with 30 minutes of 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, the researchers used wrist accelerometers: wearable devices that measure movement and inactivity, providing accurate data on physical activity levels. Wrist-worn accelerometers are imperfect at detecting posture, but are still much better than self-reporting.

These small, wearable devices measure movement in multiple directions, providing objective, minute-by-minute data on activity levels. Compared to traditional methods such as self-reporting, accelerometers offer much better accuracy and reliability. The researchers found that participants substantially overestimated their exercise and underestimated their sedentary behavior. Although imperfect, these accelerometers still provide a much better insight into how much people actually move.

Widespread adoption of accelerometers opens new doors to truly understand and address public health challenges. These devices could be used in larger and more diverse populations, providing real-world insights into daily activity patterns. As technology advances, accelerometers can also integrate with other tools, such as 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 long is bad for your heart. But the good news is that the risks can be reduced. Here are some simple strategies to help you reduce your sedentary time:

• Set timers to remind you to stand or lie down every 30 minutes.
• Include walking encounters or phone calls during your day of work.
• Use active transport such as cycling or walking for short journeys.
• Replaces screen time with light chores, gardening or hobbies that involve exercise.

Your heart is the engine that keeps your body going, and every little step you take can make it stronger. 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 have big health benefits.

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

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