Get Up, Stand Up: Uninterrupted Sedentary Time Tied to CVD in Older Women

Patrice Wendling

February 21, 2019

A prospective study underscores the benefits of being mobile for reducing cardiovascular disease (CVD) in older women and suggests that the way sedentary time is accumulated might be equally relevant for cardiovascular health.

After tracking women 63 to 97 years of age for nearly 5 years with accelerometers, researchers found a dose–response relationship between sedentary time and cardiovascular risk, such that each additional hour of sedentary time, on average, was associated with a 12% increase in adjusted CVD risk (hazard ratio [HR], 1.12; 95% CI, 1.05 - 1.19).

Further, women with the most prolonged, uninterrupted periods of sitting or lying down had a 54% higher adjusted CVD risk than women with the most regularly interrupted bouts of sedentary behavior (HR, 1.54; 95% CI, 1.17 -2.02), the team reports.

Their findings were published online February 19, 2019 in Circulation, part of the third annual Go Red for Women issue.

Exactly how long is too long to be sitting at one period of time is still open for debate and the subject of several ongoing studies, explained lead author John Bellettiere, PhD, research fellow of cardiovascular disease epidemiology, University of California, San Diego (UCSD). What's novel here is that participants who sat for longer periods had higher CVD risk than those who continually interrupted their sitting throughout the day.

"People compare it to driving a five-speed manual transmission, where sitting down is like being in reverse. Everybody needs to reverse some time, but you can't expect to skip the first few gears and go all the way to fifth gear, which is exercise," Bellettiere told theheart.org | Medscape Cardiology. "It looks like from our study that there is benefit from just breaking up your sitting with any kind of standing or moving; it doesn't have to be exercise."

Senior study author Andrea LaCroix, MPH, PhD, professor and chief of epidemiology, family medicine and public health at UCSD, cautioned that the correlations of sedentary time and mean bout duration with CVD are not causation. However, this is the first prospective study of fatal and nonfatal CVD events that used objective measures of sedentary time in a wide range of women, nearly half of whom were older than 80 years.

"More vigorous exercise is always better," LaCroix told theheart.org | Medscape Cardiology. "The issue is that for most older women saying, 'Hey, you should go out and do more moderate or vigorous physical activity,' is something like saying, 'you should climb Mount Kilimanjaro and if you can't climb Mount Kilimanjaro, this risk factor is not modifiable for you.'"

"The current physical activity guidelines say 'if you can't do moderate, vigorous exercise, do as much as you can do' and I think it says that because the mortality studies thus far support that," she observed. "The question is whether the heart disease studies follow suit or does your heart require more intense physical activity."

OPACH Study

The study involved 5638 community-dwelling older women with no history of myocardial infarction (MI) or stroke enrolled from 2012 to 2014 in the Objectively Measured Physical Activity and Cardiovascular Health (OPACH) study, a subcohort of the Women's Health Initiative. Unlike previous trials that relied on self-report, physical activity was measured using accelerometers worn over the right hip 24 hours a day for 7 consecutive days. Consecutive minutes with less than 100 counts per minute were classified as sedentary bouts.

The women were followed through February 2017 and categorized into four quartiles based on total daily sedentary time (Q1, 197 - 495 min; Q2, 496 - 555 min; Q3, 556 - 616 min; Q4, 617 - 845 min) and mean sedentary bout duration (Q1, 2.6 - 5.6 min; Q2, 5.7 - 6.8 min; Q3, 6.9 - 8.4 min; Q4, 8.5 - 52.4 min).

Over 19,350 person-years of follow-up, 545 incident CVD and 137 coronary heart disease (MI or CVD death) events occurred. CVD rates in sedentary time quartiles 1, 2, 3, and 4 were 15.0, 26.0, 30.2, and 42.9 per 1000 person-years, respectively.

Women in the highest quartile were older, more likely to be white, had the highest body mass index (BMI), and often had less favorable cardiometabolic biomarker levels.

After adjustment for potential confounders, women in the highest quartile of sedentary time had a 69% higher risk for CVD than women in the lowest quartile (HR, 1.69; 95% CI, 1.27 - 2.26), the authors report.

CVD rates also increased in a dose-dependent manner over increasing quartiles of mean sedentary bout duration, with rates of 17.1, 22.4, 30.3, and 44.3 per 1000 person-years in quartiles 1, 2, 3, and 4, respectively. CVD risk was 4% higher for each additional minute of mean sedentary bout duration (HR, 1.04; 95% CI, 1.01 - 1.07).

Women with the highest sedentary time and highest bout durations had the greatest CVD risk. Age, BMI, physical functioning, moderate to vigorous physical activity, and race/ethnicity did not appear to modify the effect of sedentary time or bout duration on CVD risk.

Reducing sedentary time by just an hour a day was associated with a 26% decrease in risk for the secondary outcome of coronary heart disease.

"We live in a society that absolutely treasures, absolutely aggrandizes any technology that helps us move less and then we think that exercise, getting a purposeful activity, is the antidote," LaCroix said. "I think what this paper suggests we do is sit less than 8 and a half hours a day and break up sitting, even if it's just getting up and standing or walking about the room or getting the mail."

The investigators previously reported from OPACH that high sedentary time and prolonged sedentary bouts are associated with higher odds of diabetes, but found no significant association for breaks in sedentary time. American Diabetes Association recommendations call for overall reductions in sedentary time and regularly interrupting long sedentary bouts, but cardiovascular societies have yet to endorse the latter, the authors noted.

Reached for comment, Joseph Hill, MD, chief of cardiology, University of Texas Southwestern Medical Center, Dallas, said the study provides new information for the cardiology community.

"To my knowledge, this is the first time that a bout of sedentary behavior is also associated with risk, not just the average over the course of your entire day," he said. "We have focused largely on not being sedentary and exercising but this notion that just a bout of extended sedentary behavior is a risk as well is a relatively new notion, that just getting up from your chair on a regular basis is associated with benefit as well."

That said, further research is needed to understand if there is a causal link, Hill said. "Common sense would suggest there probably is but we have to interpret this with a little bit of caution because this is epidemiology and an association at this point."

Commenting further, Hill said, "This is an objective evaluation based on use of an accelerometer and with all these devices that we wear on our wrists, we can now start to study this better. How much benefit can be derived from interrupting sedentary bouts of time is an area that is now ripe for further investigation."

LaCroix said they are conducting a 3-month public health study to see if just interrupting sitting is enough to change cardiovascular risk. New insights are also expected from the ongoing Women's Health Initiative Strong and Healthy Study evaluating whether a physical activity intervention conducted primarily by mail that encourages participants to sit less and move more will decrease adjudicated cardiovascular events at 4 years in a cohort of nearly 50,000 women.

Although the OPACH study used accelerometers to objectively measure sedentary behavior, the authors note that their placement over the right hip and the data-processing protocol could have misclassified standing still as sedentary time and was not ideal for measuring transitions from sitting to standing. Other limitations are that the 7-day time period might not have fully captured the usual sedentary time in all women and there were few women with low sedentary time and high bout duration or high sedentary time. Finally, the results cannot be generalized to older men or to younger women or men.

The study was funded by the National Heart, Lung, and Blood Institute (NHLBI), part of the National Institutes of Health. The authors report no relevant financial conflicts of interest. Hill is editor-in-chief of Circulation.

Circulation. Published online February 19, 2019. Abstract

Follow Patrice Wendling on Twitter: @pwendl. For more from theheart.org | Medscape Cardiology, follow us on Twitter and Facebook.

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