Published Papers - Abstract 865

Ekelund U, Steene-Johannessen J, Brown W J, Fagerland M W, Owen N, Powell K E, Bauman A, Lee I-M, for the Lancet Physical Activity Series Working Group and the Lancet Sedentary Behaviour Working Group Does physical activity attenuate, or even eliminate the detrimental association of sitting time with mortality? A harmonised meta-analysis of data from more than one million men and women. The Lancet, 2016; 388(10051): 1302-1310

Background: High amounts of sedentary behaviour have been associated with increased risks for several chronic conditions and mortality. However, it is unclear whether physical activity attenuates or even eliminates the detrimental effects of prolonged sitting. Methods: We included data from 16 studies, of which 14 were identified through a systematic review of six databases from database inception until October 2015 and two were additional unpublished studies where pertinent data were available. All study data were analysed according to a harmonised protocol, which categorized reported daily sitting time and TV-viewing time into four standardised groups each, and physical activity into quartiles. We then combined data across all studies (N=1,005,791) to analyse the joint and stratified associations of daily sitting time and physical activity with all-cause mortality, and estimated summary hazard ratios using Cox regression. We repeated these analyses using TV-viewing time instead of daily sitting time. Findings: Daily sitting time was not associated with higher all-cause mortality rates among those in the most active quartile. Compared with the referent (<4 h of sitting per day and highest quartile of physical activity [>35.5 MET-hour/week]), there was no increased risk of dying during follow up in those who sat for more than 8h/day but who also reported >35.5 MET-hour/week of activity (HR=1.04; 95% CI, 0.99, 1.10). In contrast, those who sat the least (<4 h/day) and were in the lowest (<2.5 MET- 3 hour/week) activity quartile had a significantly increased risk of dying during follow-up (HR=1.27, 95% CI, 1.22, 1.31). For TV viewing time, >3 hours/day was associated with higher mortality rates regardless of physical activity, except in the most active quartile, where mortality rates were significantly higher only in the >5 hours/day group. Interpretation: High levels of moderate intensity physical activity (i.e. about 60 to 75 minutes per day) appear to eliminate the increased risk of death associated with high sitting time. However, this high activity level attenuates, but does not eliminate the increased risk associated with high TV viewing time. Funding: None