For years, medical professionals and media personalities alike have warned against sitting for prolonged periods, coining the phrase “sitting is the new smoking” to describe the health risks of a sedentary lifestyle. But how much is too much? Keith M. Diaz, MD, and a team of researchers spent more than four years trying to objectively answer that question.
Diaz and his team designed a prospective cohort study of nearly 8,000 American adults that would measure, through an accelerometer, how much time participants spent being sedentary each day and for how long. Unsurprisingly, less motion meant greater risk for heart disease and all-cause mortality—previous research had already proven that to be true. But, Diaz and co-authors note in their paper, former studies have been almost entirely based on subjective data, which is likely to contain reporting bias and human error. In addition, no previous studies have explored the relationship between length of sedentary periods and risk of mortality.
“As an exercise physiologist, I have always viewed exercise as a critical health behavior that can prevent and help treat many chronic diseases,” Diaz said in an email. “When some of the initial studies on sitting first started being published, this notion that exercise could not overcome the hazards of sitting was stunning. Intrigued by these early findings, I have focused my research efforts on studying sitting and its harmful consequences in hopes of helping to determine what we can do about it to help the public.”
The researchers drew a sample of 7,985 black and white adults, all of whom were at least 45 years old at the time, from the REGARDS (Reasons for Geographic and Racial Differences in Stroke) study. They fitted each participant with an accelerometer, which was worn on the person’s right hip, and instructed subjects to wear the gadget during waking hours for seven consecutive days. Activity count was summed in one-minute increments.
Diaz’s team followed up with study participants every six months for an average of four years. During that time, 340 patients died—and that cohort was associated with both greater total sedentary time and longer sedentary bout duration. Researchers found that all-cause mortality wasn’t affected by age, sex, race, cardiovascular risk factors, BMI or moderate- to vigorous-intensity physical activity.
Indeed, regardless of a person’s exercise regimen, the study’s results showed that accumulation of sedentary time in stretches of 60 to 89 and 90 or more minutes at once was associated with greater risk of death, no matter the cause. The interval of 1 to 29 minutes was linked to the least risk of all-cause mortality, which is in line with current physical activity guidelines.
Diaz and co-authors noted that while current guidelines recommend minimizing sedentary time in all age groups, they don’t specify how the American population can reduce time spent sitting down. According to the study, sedentary behavior accounted for a large majority—more than 77 percent—of all waking hours in participants, which is equivalent to 12.3 hours per 16-hour waking day. A person would likely need between 60 and 75 minutes a day of moderate-to-vigorous exercise to rectify the damage done to their bodies by sitting for those prolonged periods.
“The American Heart Association’s current recommendations are ‘Sit Less, Move More,’” Diaz said. “This would be like telling someone to just ‘exercise’ without telling them how. With exercise, guidelines recommend how often, long long, at what intensity and what exercise type. We need similar guidelines for sitting. We think a more specific guideline would be ‘For every consecutive 30 minutes of sitting, stand up and move or walk for 5 minutes at a brisk pace to reduce the health risks from sitting.”
Participants who recorded the most total sedentary time were more likely to be older, black, smoke and not live in a stroke belt or buckle region, Diaz’s research states. They were also more likely to have diabetes, high blood pressure, dyslipidemia, a higher BMI, atrial fibrillation and history of heart disease and stroke.
Diaz said he thinks the country as a whole would benefit from rethinking the workplace, from the actual environment and more movement-conducive space design to changing policies so employees would be allowed to take “brief movement breaks.”
In addition, he said, doctors should be emphasizing the importance of movement during medical visits.
“I think this should serve as a wake-up call to physicians that they should be encouraging their patients to move frequently throughout the day,” Diaz said. “Exercise—as hard as it is already to get patients to do—may not be enough. And, as patients’ age and their physical and mental function declines, they become more and more sedentary. So, there is an urgent need to get patients up off their chairs, couches and beds is we want to improve their quality of life and lifespan.”