In many computer-based jobs, when the heavy workload keeps us glued to our seats without even taking a bathroom break, we lose track of time and can spend hours without moving. Even if your boss gives you a disapproving look, make sure to get up every now and then and walk, climb stairs, or move minimally because it's not enough to go hiking on weekends or play a game with friends after work, that doesn't compensate for the risk of cardiovascular disease and death associated with sitting (or reclining/lying down) for more than 10 hours a day.
This is indicated by a study published in JACC, the flagship journal of the American College of Cardiology, presented at the 2024 American Heart Association (AHA) Scientific Sessions. The study shows that more than 10 and a half (10.6) hours of sedentary behavior per day is significantly related to future heart failure and cardiovascular death, even among individuals who meet the recommended levels of exercise.
It is not new that lack of exercise is a risk factor for cardiovascular disease, and in fact, current guidelines recommend more than 150 minutes of moderate to vigorous physical activity per week to promote heart health. However, the experts in this study say that exercise is only a small fraction of the total daily activity and that current guidelines do not provide specific guidance on sedentary behavior, which represents a much larger part of daily activity, despite evidence that it is directly related to the risk of cardiovascular disease.
Therefore, this study examined the amount of sedentary time at which the risk of cardiovascular disease is higher and analyzed how sedentary behavior and physical activity together impact the odds of atrial fibrillation (arrhythmia), heart failure, myocardial infarction, and cardiovascular mortality. It included 89,530 participants from the UK Biobank (a huge database that has been collecting information from half a million Britons since 2006), 56.4% of whom were women with an average age of 62. The data came from a triaxial accelerometer worn on the wrist that recorded movement for seven days, with an average sedentary time per day of 9.4 hours.
After an average follow-up of eight years, 3,638 individuals (4.9%) developed atrial fibrillation, 1,854 (2.1%) developed heart failure, 1,610 (1.84%) developed myocardial infarction, and 846 (0.94%) died from cardiovascular causes, respectively.
The effects of sedentary time varied depending on the outcome. In the case of atrial fibrillation and myocardial infarction, the risk increased steadily with time without significant changes. In the case of heart failure and cardiovascular mortality, the increased risk was minimal until sedentary time exceeded 10.6 hours per day, at which point the risk increased significantly, showing a 'threshold' effect for behavior.
For participants who met the recommended 150 minutes of moderate to vigorous physical activity or more, the effects of sedentary behavior on the risks of atrial fibrillation and myocardial infarction were substantially reduced, but the effects on a higher risk of heart failure and cardiovascular mortality remained prominent.
"Future guidelines and public health initiatives should emphasize the importance of reducing sedentary time. Avoiding sitting for more than 10.6 hours a day can be a realistic minimum goal for better heart health," emphasizes Khurshid.
In an accompanying editorial comment, Charles Eaton, director of the Director of Family Medicine Research as well as the Brown University Center, points out that the use of wearable accelerometers has shown that exercise is significantly overestimated when people self-report their exercise, and sedentary behavior is underestimated.
According to Eaton, simply replacing 30 minutes of excessive sitting time each day with any type of physical activity can reduce risks for heart health. Adding moderate to vigorous activity reduced the risk of heart failure by 15% and cardiovascular mortality by 10%, and even engaging in light activity made a difference by reducing the risk of heart failure by 6% and cardiovascular mortality by 9%.
For Harlan M. Krumholz, Harold H. Hines Jr. Professor at the Yale School of Medicine and editor-in-chief of JACC, this study contributes "to the growing evidence of the strong link between sedentary behavior and cardiovascular health. The findings strongly suggest that we need people to move to promote better health."
The study has several limitations, including the inability to know details about where and why people remain seated or lying down for extended periods, such as in the workplace, which could have different effects on cardiovascular risks. Wrist-worn accelerometers are imperfect for detecting posture and could misclassify time spent standing as sedentary time. The researchers point out that a longer follow-up period may provide more accurate data on habits and activity patterns.
"The strength of the study is that it includes many patients, the follow-up is long, and it has good activity measurement because everyone has that device, an accelerometer, so it's not a questionnaire because many previous studies are like those on diet: they ask people, and people always think they move much more than they do (or eat less than they do), whereas here it is objective," comments Ignacio Fernández Lozano, president-elect of the Spanish Society of Cardiology (SEC).
For Fernández, the key is not to say that exercise is good because that is already known, "but that being sedentary for a long time, specifically more than 10.6 hours a day, is clearly associated with a higher incidence of cardiovascular events: myocardial infarction, atrial fibrillation, heart failure, and cardiovascular mortality. What sets this study apart is that not only the level of exercise matters, but being still for more than 10 and a half hours is harmful, that's the key issue."
And that sedentary behavior, he emphasizes, is not compensated for by doing a lot of exercise. "It's better to be less still and move more." The specialist acknowledges that it can be challenging at times, but one must force oneself "to break up that prolonged sitting time: try to intersperse it with a small activity, take the opportunity to run an errand and walk, if you work in a four-story office, don't take the elevator (all advice, obviously, adapted with common sense to personal circumstances), walk home for lunch if possible, take a stroll around the block...". You know it, 'micro-breaks of activity' to break up those long hours sitting, even if your bosses give you disapproving looks.