Does physical activity attenuate, or even eliminate, the detrimental association of sitting time with mortality? A harmonised meta-analysis of data from more than 1 million men and women.
Level 3 - non-randomized controlled study
Systematic review and meta-analysis of prospective cohort studies
PubMed 27475271 · doi:10.1016/S0140-6736(16)30370-1
What was done
A systematic review across six databases up to October 2015 identified prospective cohort studies with individual-level exposure and outcome data on daily sitting or TV-viewing time, physical activity, and mortality. Data from 16 cohorts (14 published, 2 unpublished) were harmonised using standardised categories for sitting/TV time and physical activity quartiles (in MET-hours per week). Individual participant data were pooled and analysed for all-cause mortality using Cox proportional hazards regression.
What was found
In 13 studies with sitting data (1,005,791 individuals, 84,609 deaths over 2 to 18.1 years follow-up), mortality was 12% to 59% higher in the two lowest physical activity quartiles compared to the referent group (sitting <4 h/day and >35.5 MET-h/week). Hazard ratios ranged from 1.12 (95% CI: 1.08-1.16) for sitting <4 h/day and physical activity <16 MET-h/week, up to 1.59 (95% CI: 1.52-1.66) for sitting >8 h/day and physical activity <2.5 MET-h/week. In the highest activity quartile (>35.5 MET-h/week), sitting >8 h/day was not associated with increased mortality (HR 1.04, 95% CI: 0.99-1.10). In 6 studies on TV-viewing (465,450 individuals, 43,740 deaths), TV viewing for 3 or more hours per day increased mortality across all activity levels except the highest quartile, where risk was increased only at 5 or more hours per day (HR 1.16, 95% CI: 1.05-1.28).
Why it matters
This study demonstrates that the elevated all-cause mortality risk from prolonged sitting can be eliminated by approximately 60 to 75 minutes of moderate-intensity physical activity per day.
Limits
Sitting, TV-viewing, and physical activity levels were self-reported, leaving potential for measurement error and recall bias. Because the included studies are observational, residual confounding and reverse causation cannot be fully ruled out. Additionally, high activity attenuated but did not fully eliminate the mortality risk associated with very high TV-viewing time (5 or more hours per day).
Cited by
- context Sedentary behavior increases the risk of premature death independently of whether an individual engages in physical activity.