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Being sedentary is harmful even for active people

Lounging around or lying down for more than 10.6 hours during the day increases risk of cardiovascular disease and death, even for people who exercise regularly.

It has previously been understood that extensive periods of sedentary behaviour such as sitting, reclining and lying down indicated a lack of essential physical activity, but a new study published in the Journal of the American College of Cardiology (JACC) suggests the impact is worryingly worse.

“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 Shaan Khurshid, 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.”

The researchers studied more than 89,000 participants who wore a wrist accelerometer that captured movement over seven days, with the average sedentary time per day 9.4 hours.

Eight years later, 4.9% had developed atrial fibrillation (AF), 2.1% heart failure (HF), 1.9% myocardial infarction (MI) and 0.94% cardiovascular (CV) mortality.

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 the risk rose significantly, showing a “threshold” effect for the behaviour.

For study participants who met the recommended 150 minutes or more of moderate-to-vigorous physical activity each week, the effects of sedentary behaviour 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 says. “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, director of the Brown University Department of Family Medicine, says the use of wearable accelerometers has shown that exercise is significantly over estimated by self-reporting and sedentary behaviour is underestimated.

Eaton says 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%.

“This study adds to the growing evidence of a strong link between sedentary behaviour and cardiovascular health,” say Harlan Krumholz, junior professor at Yale School of Medicine, and Harold Hines, editor in chief of JACC

“The findings strongly suggest that we need to get people moving to promote better health.”

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