How Many Hours of Sitting Is Too Much for Your Heart?
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A recent study highlights that more than 10.5 hours of daily sedentary behavior is linked to increased risks of heart failure and cardiovascular death, regardless of exercise habits.
Over 89,000 participants were analyzed to establish that even active individuals are at risk if they sit or recline too much, suggesting a crucial threshold for sedentary time that impacts heart health.
Link Between Sedentary Behavior and Cardiovascular Risk
Spending more time sitting, reclining, or lying down during the day may raise the risk of cardiovascular disease (CVD) and death, according to a study published today (November 15) in JACC, the flagship journal of the American College of Cardiology, and presented at the American Heart Association’s Scientific Sessions 2024. The research found that exceeding 10.5 hours of sedentary behavior daily is strongly associated with an increased risk of heart failure (HF) and cardiovascular (CV) death, even among individuals who meet exercise recommendations.
“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.”
Study Findings on Sedentary Time and Exercise
Insufficient exercise is a known risk factor for cardiovascular disease (CVD). Over 150 minutes of moderate-to-vigorous physical activity per week is recommended by current guidelines to promote heart health. However, study experts say exercise is only a small fraction of overall daily activity, and the current guidelines don’t provide specific guidance on sedentary behavior which accounts for a much larger portion of daily activity, despite evidence that it’s directly linked with CVD risk.
This study examined the amount of sedentary time at which CVD risk is greatest and explored how sedentary behavior and physical activity together impact the chances of atrial fibrillation (AF), heart failure (HF), myocardial infarction (MI), and CV mortality.
Study Data and Risk Thresholds
Among the 89,530 study participants of the UK biobank, the average age was 62 years and 56.4% were women. Participants submitted data from a wrist-worn triaxial accelerometer that captured movement over seven days. The average sedentary time per day was 9.4 hours.
After an average follow-up of eight years, 3,638 individuals (4.9%) developed incident AF, 1,854 (2.1%) developed incident HF, 1,610 (1.84%) developed indecent MI and 846 (0.94%) died of CV causes, respectively.
The effects of sedentary time varied by outcome. For AF and MI, the risk increased steadily over time without major shifts. For HF and CV mortality, increase in risk was minimal until sedentary time exceeded about 10.6 hours a day, at which point risk rose significantly, showing a “threshold” effect for the behavior.
Impact of Reducing Sedentary Time
For study participants who met the recommended 150 minutes of moderate-to-vigorous physical activity or more, the effects of sedentary behavior on AF and MI risks were substantially reduced, but effects on higher risk of HF and CV mortality remained prominent.
“Future guidelines and public health efforts should stress the importance of cutting down on sedentary time,” Khurshid said. “Avoiding more than 10.6 hours per day may be a realistic minimal target for better heart health.”
In an accompanying editorial comment, Charles Eaton, MD, MS, Director of the Brown University Department of Family Medicine, said the use of wearable accelerometers has shown that exercise is significantly over-estimated by self-report and sedentary behavior is under-estimated.
Eaton said that replacing just 30 minutes of excessive sitting time each day with any type of physical activity can lower heart health risks. Adding moderate-to-vigorous activity cut the risk of HF by 15% and CV mortality by 10%, and even light activity made a difference by reducing HF risk by 6% and CV mortality by 9%.
Study Limitations and Future Directions
“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.”
There are several limitations of the study, including the inability to know details on where or why people are sitting or lying down for extended periods, such as at the workplace, which could have different impacts on CV risks. Accelerometers worn on the wrist are imperfect at detecting posture and therefore may misclassify standing time as sedentary time. A longer monitoring period may provide more accurate data on activity habits and patterns.
Other limitations include the potential for confounders in study results, selection bias, the inability to measure the actual effects of reallocating sedentary time to other activities, and differences between data from wrist-worn accelerometers versus thigh-worn accelerometers.
Reference: “Accelerometer-Measured Sedentary Behavior and Risk of Future Cardiovascular Disease” 15 November 2024, Journal of the American College of Cardiology.
DOI: 10.1016/j.jacc.2024.10.065
