Patterns of Sedentary Behavior and Mortality in U.S. Middle-Aged and Older Adults: A National Cohort Study

Abstract

Background: Excessive sedentary time is ubiquitous in Western societies. 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.

Objective: To examine the association between objectively measured sedentary behavior (its total volume and accrual in prolonged, uninterrupted bouts) and all-cause mortality.

Design: Prospective cohort study.

Setting: Contiguous United States.

Participants: 7985 black and white adults aged 45 years or older.

Measurements: Sedentary time was measured using a hip-mounted accelerometer. Prolonged, uninterrupted sedentariness was expressed as mean sedentary bout length. Hazard ratios (HRs) were calculated comparing quartiles 2 through 4 to quartile 1 for each exposure (quartile cut points: 689.7, 746.5, and 799.4 min/d for total sedentary time; 7.7, 9.6, and 12.4 min/bout for sedentary bout duration) in models that included moderate to vigorous physical activity.

Results: Over a median follow-up of 4.0 years, 340 participants died. In multivariable-adjusted models, greater total sedentary time (HR, 1.22 [95% CI, 0.74 to 2.02]; HR, 1.61 [CI, 0.99 to 2.63]; and HR, 2.63 [CI, 1.60 to 4.30]; P for trend < 0.001) and longer sedentary bout duration (HR, 1.03 [CI, 0.67 to 1.60]; HR, 1.22 [CI, 0.80 to 1.85]; and HR, 1.96 [CI, 1.31 to 2.93]; P for trend < 0.001) were both associated with a higher risk for all-cause mortality. Evaluation of their joint association showed that participants classified as high for both sedentary characteristics (high sedentary time [≥12.5 h/d] and high bout duration [≥10 min/bout]) had the greatest risk for death.

Limitation: Participants may not be representative of the general U.S. population.

Conclusion: Both the total volume of sedentary time and its accrual in prolonged, uninterrupted bouts are associated with all-cause mortality, suggesting that physical activity guidelines should target reducing and interrupting sedentary time to reduce risk for death.

Primary funding source: National Institutes of Health.

Figure 1. Adjusted cumulative mortality by total sedentary time (Panel A) and mean sedentary bout duration (Panel B) quartiles

Models adjusted for age, sex, race, region of residence, education, season, current smoking, alcohol use, body mass index, diabetes, hypertension, dyslipidemia, estimated glomerular filtration rate <60 mL/min/1.73 m2, atrial fibrillation, history of coronary heart disease, history of stroke, and moderate-vigorous physical activity. The quartile cutoff points were <689.7, ≥689.7 to <746.5, ≥746.5 to <799.4, and ≥799.4 min/day for total sedentary time and <7.7, ≥7.7 to <9.6, ≥ 9.6 to <12.4, and ≥12.4 min/bout for sedentary bout duration.

Figure 2. Hazard ratio of all-cause mortality as a function of total sedentary time (Panel A) and mean sedentary bout duration (Panel B) expressed continuously

Data were fitted using restricted cubic splines with the mean set as the reference and 4 knots placed at the 5^th, 35^th, 65^th, and 95^th percentiles. Results are trimmed at the 1^st and 99^th percentiles and are reported as hazard ratios (black line) and 95% confidence intervals (gray shaded area). Total sedentary time is a linear model (p-value for overall effect <0.001, p-value for non-linear relationship=0.70) and mean sedentary bout duration is a non-linear model (p-value for overall effect <0.001, p-value for non-linear relationship <0.001). Models were adjusted for age, sex, race, region of residence, education, season, current smoking, alcohol use, body mass index, diabetes, hypertension, dyslipidemia, estimated glomerular filtration rate <60 mL/min/1.73 m², atrial fibrillation, history of coronary heart disease, history of stroke, and moderate-vigorous physical activity.

Figure 3. Adjusted cumulative mortality according to joint associations of total sedentary time and prolonged, uninterrupted sedentary bouts

Models adjusted for age, sex, race, region of residence, education, season, current smoking, alcohol use, body mass index, diabetes, hypertension, dyslipidemia, estimated glomerular filtration rate <60 mL/min/1.73 m², atrial fibrillation, history of coronary heart disease, history of stroke, and moderate-vigorous physical activity. High and low groups were defined as ≥12.5 and <12.5 hours/day for total sedentary time and ≥10.0 min/bout and <10 min/bout for mean sedentary bout duration. The sample size and number of deaths for each group were as follows: low total sedentary time/low sedentary bout time (n=3,689, deaths=62), high total sedentary time/low sedentary bout time (n=628, deaths=30), low total sedentary time, high sedentary bout time (n=446, deaths=9), high total sedentary time/high sedentary bout time (n=3,222, deaths=239).

Figure 4. Adjusted cumulative mortality by quartile of sedentary bout threshold

Panel A: %Sedentary Time from Bouts 1-30 min; Panel B: %Sedentary Time from Bouts 30-60 min; Panel C: %Sedentary Time from Bouts 60-90 min; Panel D: %Sedentary Time from Bouts ≥90 min. Models adjusted for age, sex, race, region of residence, education, season, current smoking, alcohol use, body mass index, diabetes, hypertension, dyslipidemia, estimated glomerular filtration rate <60 mL/min/1.73 m2, atrial fibrillation, history of coronary heart disease, history of stroke, and moderate-vigorous physical activity. The quartile cutoff points were <42.2%, ≥42.2% to <53.0%, ≥53.0% to <62.8%, and ≥62.8% for bouts 0-30 min; <18.1%, ≥18.1% to <22.1%, ≥22.1% to <26.2%, and ≥26.2% for bouts 30-60 min; <7.6%, ≥7.6 to <11.3%, ≥11.3% to <15.5%, ≥15.5% for bouts 60-90 min; and <5.2%, ≥5.2% to <10.9%, ≥10.9% to <19.0%, and ≥19.0% for >90 min bouts.