How Much Sedentary Time Is Bad for You?

Guidelines recommend 150 minutes of moderate to vigorous exercise every week to lower the risk of cardiovascular (CV) disease. But the guidelines aren’t clear about how inactivity affects your heart.

New research from Mass General Brigham shows that more than 10.6 hours of sedentary time per day increases your risk of atrial fibrillation (AFib), heart attack, heart failure, and CV death. The study, published in the Journal of the American College of Cardiology, found that this was true even for people who also get the recommended amount of exercise per week.

“Many people spend many hours a day being sedentary. We wanted to understand whether exercise can negate the effects of sedentary behavior,” says Shaan Khurshid, MD, MPH, a Mass General Brigham cardiac electrophysiologist who cares for patients at Massachusetts General Hospital. “Overall, our findings suggest that avoiding excess sedentary behavior is important for cardiovascular benefit whether or not you’re physically active.”

How much sedentary time do most people get?

Dr. Khurshid recently completed a study that included almost 90,000 people who wore activity trackers on their wrists for 1 week. The researchers collected data on exercise time and intensity, as well as sedentary time. Sedentary time was defined as any time awake spent sitting, reclining, or lying down, and using low amounts of energy. Sleeping and standing did not count as sedentary time.

The average amount of sedentary time was 9.4 hours per day. The researchers split the participants into 4 equal groups:

• The most sedentary group had an average sedentary time of more than 10.6 hours per day.
• The next group ranged from 9.5 to 10.6 hours per day.
• Another group ranged from 8.2 to 9.4 hours per day.
• The group with the least sedentary time averaged less than 8.2 hours per day.

“A total of 10.6 hours seems like a lot. But if you think about someone who has a desk job and then watches a little TV at night, that actually adds up pretty quickly,” Dr. Khurshid says. “U.S. estimates are an average of 9.5 hours per day. So, 10.6 is greater than average, but it does represent a lot of people’s behavior.”

The effects of sedentary time on cardiovascular risk

The study then assessed how many people experienced four specific cardiovascular conditions in the next 8 years. It found that people in the highest category of sedentary behavior (more than 10.6 hours) had a higher risk of four significant heart conditions:

1. Atrial fibrillation (AFib): Atrial fibrillation is one of the most common types of irregular heartbeat, or arrhythmia. Atrial fibrillation can cause blood clots, stroke, heart failure and other complications.
2. Heart failure: In heart failure, the heart isn’t working as well as it should. The condition can prevent the rest of the body from getting the oxygen it needs.
3. Myocardial infarction (heart attack): This medical emergency happens when blood flow to the heart is blocked, preventing the heart from getting enough oxygen.
4. CV mortality: The study also examined how many people died from heart-related causes.

The findings were particularly strong for heart failure and CV death. The most sedentary people had 40% and 60% increased risk, respectively. Plus, the more days a week a person exceeded that 10.6-hour mark, the higher their risk of the 4 CV conditions.

Sitting too much affects heart health even when you meet exercise guidelines.

Interestingly, a lot of sedentary time increased the risk of heart-related problems even in people who got the recommended amount of weekly exercise.

“Being active is helpful, but it doesn’t fully overcome the risks associated with excess sedentary behavior. So even if you’re physically active, reducing your sedentary behavior is still important,” explains Dr. Kurshid.

Changing sedentary behavior to any other activity reduced risk, he emphasized.

“We looked at people in the high sedentary behavior category and analyzed what would happen to their risk if they changed sedentary behavior into anything else. Even if they just changed it to light activity. Anything but sedentary — walking, standing, basically doing anything,” Dr. Khurshid says. “We saw lower risk for heart failure and cardiovascular death. So if you can work that into the course of your day, our study suggests that will be helpful for your risk.”

Dr. Khurshid hopes that these findings will motivate people to make small changes and adopt healthy behaviors in whatever ways work for them. He recently completed a study, published in Circulation, showing that “weekend warriors” have substantially lower risk of 264 diseases compared with people who are inactive. The study found that concentrating physical activity into longer sessions only 1 or 2 days a week is just as beneficial as spreading activity more evenly throughout the week.