Long Bouts of Sedentary Time Linked to CVD Risk in Women

Older women who are sedentary for long periods of time throughout the day are at a significantly higher risk of cardiovascular events compared with women who sit less, according to the results of a new accelerometer-based study.

For each additional hour spent sitting, there is a 12% increase in the risk of cardiovascular disease (MI, revascularization, hospitalized angina, heart failure, stroke, or death from cardiovascular disease) and a 26% greater risk of coronary heart disease (nonfatal MI or coronary death), say researchers.

Speaking with TCTMD, lead investigator John Bellettiere, MD, PhD (University of California, San Diego), said that because they used an objective measure of sedentary behavior with the accelerometer, they were able to assess patterns of sitting—“that being how people accumulate their sitting throughout the day, which has never been looked at with respect to cardiovascular disease.”

For example, women in the highest quartile of prolonged sedentary behavior had more extended bouts of inactivity (mean sedentary bout duration 8.5 to 52.4 minutes) compared with women in the lowest quartile, who had more interrupted sitting patterns (mean sedentary bout duration 2.6 to 5.6 minutes). Compared with women in the lowest quartile, who Bellettiere described as “women who are always up and down throughout the course of the day,” those with the most prolonged bouts of sedentary time had a 54% increased risk of cardiovascular disease.

“Exercise is one of the key factors in preventing heart disease, but our study shows pretty good evidence that sedentary behavior might also be one of the factors that could reduce incident cardiovascular disease,” said Bellettiere. “If this is subsequently proven to be a cause-and-effect relationship, this means that for an older adult, something as simple as reducing the amount of time sitting—and it doesn’t mean you need to exercise, although shifting sitting time to exercise time would be the ultimate benefit—could potentially reduce their risk.”

Something as simple as reducing the amount of time sitting . . . could potentially reduce their risk of cardiovascular disease. John Bellettiere

Keith Diaz, PhD (Columbia University Irving Medical Center, New York, NY), who was not involved in the study but who has studied the risks of sedentary behavior, said this new analysis drives home the important message that not only does the total amount of daily sedentary time matter when it comes to cardiovascular health but sitting without moving for an extended amount of time in a day is also critical.

“They both matter,” said Diaz. “Yes, it’s about how long you sit during the day, but it’s also about sitting for these really long bouts of time. Together, they’re both really harmful. Ultimately, what we tell people is that if you want to lower your risk of death, if you’re a person that has to sit all day at work, just taking a break every 30 or 60 minutes and walking around could be one health-behavior change you make to reduce your future risk.”

The OPACH Study With Accelerometers   

The study, published February 19, 2019, in a special “Go Red for Women” edition of Circulation, is an analysis of 5,638 women aged 63 to 97 years participating in the Women’s Health Initiative. In this substudy, known as the Objective Physical Activity and Cardiovascular Health (OPACH) study, the women wore accelerometers for 4 to 7 days to assess their average daily sedentary time and mean sedentary bout duration. Previous studies have assessed the association between inactivity and cardiovascular disease, but this study is the first to use an objective measure of sedentary behavior.

“There’s problems with self-reported measures,” said Bellettiere. “People have a hard time recalling how much time they spend sitting, so there’s a lot of error in those measures. When you’re running studies or associations with measures that have error, the estimates you get might not reflect the true effect estimate. That seems to be the case here. We found significantly larger effect sizes than what was found previously in studies that relied on self-reporting.”

Compared with women in the first quartile—those who were sedentary for roughly less than 9 hours per day—those in the fourth quartile, who were sedentary for 11 or more hours per day, had a 62% increased risk of cardiovascular disease. Notably, even after adjusting for moderate-to-vigorous physical activity, the association between sedentary time and cardiovascular disease remained statistically significant.

Diaz, who published an analysis in 2017 showing that prolonged, uninterrupted sedentary time was associated with impaired glycemic control in US Hispanic/Latino adults, said they frequently try to remind individuals that the risk of sedentary behavior is independent of physical activity.

“You can’t just exercise in the morning and think you’ve checked off your activity box and sit the rest of the day,” he told TCTMD. “We’re still learning about physical activity. We still don’t know all that much. We’re learning that optimal physical activity is just someone who is moving throughout the day. And yes, more intense activity is better, but even light intensity still has benefits. It’s about moving and moving throughout your day. It’s not just about exercising for 30 minutes and thinking you’re done.”

It’s about how long you sit during the day, but it’s also about sitting for these really long bouts of time. Keith Diaz

The researchers make similar arguments, noting that regular interruptions when sedentary, such as getting up during commercial breaks while watching television, lower sedentary bout durations and subsequently lower cardiovascular risk.

For Diaz, these new results are particularly exciting given that it’s among the first to link device-measured sedentary behavior with the risk of cardiovascular disease.

“These questionnaires that we use to try to study sitting time are terrible,” said Diaz. “Ask somebody, ‘How many hours a day do you sit?’ That’s really hard for somebody to answer, so using these devices is really the best way for us to figure how much a person sits and whether that’s actually linked to future risk.”  One of the next steps, said Diaz, will be to assess the relationship between objectively measured sedentary behavior and cardiovascular disease in a younger population.