December 30, 2024
We know that too much sitting is bad for us, but a new study adds an important detail: if you spend more than 10-and-a-half hours a day sitting or lying down, regular exercise might not be enough to prevent an increased risk of serious heart issues.
It's an extra layer to our understanding of the push and pull between the dangers of a sedentary lifestyle and activities that might protect us against those health consequences.
The researchers behind the study, led by a team from the Broad Institute of MIT and Harvard, suggest that guidelines should be introduced for the maximum time people should spend sitting – as well as the minimum time they should spend exercising.
"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," says cardiologist Shaan Khurshid, from Massachusetts General Hospital and the Broad Institute.
"Too much sitting or lying down can be harmful for heart health, even for those who are active."
The study analyzed activity data from 89,530 people, with an average age of 62, who were asked to wear fitness trackers for a week. This data was referenced against the longer-term health of the cohort, across an average follow-up period of 8 years.
The median sedentary time was 9.4 hours a day, but at 10.6 hours-per-day there seemed to be an inflection point. Those who sat for at least 10.6 hours had a 40 percent higher risk of heart failure and a 54 percent higher risk of cardiovascular mortality compared to those who sat less.
Individuals who did not regularly exercise faced the greatest health risks from this much daily sedentary time, but even those who did manage 150 minutes or more of moderate-to-vigorous physical activity per week still showed health repercussions.
Those who sat for 10.6 hours or more but who met exercise recommendations were 15 percent more likely to suffer heart failure and 33 percent more likely to die from a cardiovascular-related issue compared to those who sat less.
While we've seen previous studies that talk about how to 'offset' sitting with exercise, physical activity might not reverse all the health downsides, according to this latest research.
The collected data isn't comprehensive enough to prove cause and effect between sitting and major heart issues, but there is enough evidence here to suggest they're related.
The researchers point to the large sample size and the use of wearables – together with machine learning analysis – as strengths of the study. Many studies rely on self-reporting from the participants, and people tend to underestimate how much time they spend sitting each day.
Of course, this doesn't mean exercise doesn't matter – we've seen many times over that any increase in activity, even small ones, can help improve health – but it's also important to keep track of how much sitting we're doing, too.
"Future guidelines and public health efforts should stress the importance of cutting down on sedentary time," says Khurshid.
"Avoiding more than 10.6 hours per day may be a realistic minimal target for better heart health."
The research has been published in the Journal of the American College of Cardiology.
