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Excessive sedentary time increases risk for all-cause mortality

Regardless of physical activity level, high total volume of sedentary time accumulated throughout the day and its accrual in prolonged, uninterrupted bouts were associated with a significant risk for all-cause mortality, according to findings published in the Annals of Internal Medicine.

“Adults are sedentary for an alarming 9 to 10 hours per day. ... Evidence indicates that sedentary time is associated with incident cardiovascular disease, incidence of cardiovascular disease-related risk factors, and mortality,” Keith M. Diaz, PhD, from Columbia University Medical Center and Weill Cornell Medical, New York, and colleagues wrote.

However, “Previous studies have relied on self-reporting to evaluate the total volume of sedentary time as a prognostic risk factor for mortality and have not examined whether the manner in which sedentary time is accrued (in short or long bouts) carries prognostic relevance,” the researchers added.

Diaz and colleagues sought to determine the relationship between sedentary behavior measured objectively through both total volume and accrual in prolonged, uninterrupted bouts and all-cause mortality. They included 7,985 black and white adults aged 45 years or older from the REGARDS study.

Participants wore a hip-mounted accelerometer during waking hours for 7 consecutive days. Data from the accelerometer were used to measure sedentary time. Sedentary behavior, light-intensity physical activity and moderate-to-vigorous intensity physical activity were defined as measurements of 0 to 49, 50 to 1,064, and at least 1,065 counts per minute, respectively. The researchers compared quartiles 2 through 4 to quartile 1 for total sedentary time (quartile cut points, 689.7, 746.5 and 799.4 minutes/day) and sedentary bout duration (quartile cut points, 7.7, 9.6 and 12.4 minutes/bout) to calculate HRs.

During follow-up (median, 4 years), 340 participants died. For 77.4% of wear time or approximately 12.3 hours over a 16-hour waking day, participants demonstrated sedentary behavior. Participants had a mean sedentary bout length of 11.4 minutes.

A total of 52%, 22.1%, 11.8% and 14.1% of total sedentary time accumulated in bouts of 0 to 29, 30 to 59, 60 to 89, and 90 or more minutes, respectively.

A higher all-cause mortality risk was associated with both greater total sedentary time (HR = 1.22; 95% CI, 0.74-2.02; HR = 1.61; 95% CI, 0.99-2.63; and HR = 2.63; 95% CI, 1.60-4.30; P for trend < .001) and longer sedentary bout duration (HR = 1.03; 95% CI, 0.67-1.60; HR = 1.22; 95% CI, 0.80-1.85; and HR = 1.96; 95% CI, 1.31-2.93; P < .001). This association did not vary by age, sex, race, BMI or exercise habits.

The greatest risk for mortality was observed in participants with both a high sedentary time (12.5 hours/day) and high bout duration (10 minutes/bout), while the lowest risk for death was seen in those who kept their sitting bouts under 30 minutes.

“In a geographically diverse, biracial, population-based sample of middle-aged and older U.S. adults, both total sedentary time and prolonged, uninterrupted sedentary bouts were associated with an increased risk for all-cause mortality, independent of physical activity levels,” Diaz and colleagues concluded. “Our findings suggest that total sedentary time and prolonged, uninterrupted sedentary bouts are jointly associated with increased risk for death and that interrupting sedentary time every 30 minutes may protect against the health risks incurred by prolonged sedentariness. These data may be useful to inform specific recommendations for reducing sedentary behavior and support the concept that reducing and regularly breaking up sedentary time may be an important adjunct to existing physical activity guidelines.”

In an accompanying editorial, David A. Alter, MD, PhD, from the University of Toronto, wrote that the findings by Diaz and colleagues shed light on the effects of sedentary behaviors on mortality.

“Daily sedentary time, uninterrupted sedentary bout length, and moderate to vigorous physical activity may each play an important and distinct role in long-term health behaviors and survival,” he wrote. “Interventions with the greatest effect on population outcomes may be those that take each into account.” – by Alaina Tedesco

Disclosures: Diaz and Alter report no relevant financial disclosures. Please see the study for all other authors’ relevant financial disclosures.