1. In two cohorts from the UK Biobank and the National Health and Nutrition Examination Survey (NHANES), there was an increased risk of death from respiratory disease, cardiovascular disease, cancer, and an increased risk for all-cause mortality associated with sedentary behaviour (SB).  

2. Substituting SB with physical activity was associated with a decreased risk of mortality. 

Evidence Rating Level: 1 (Excellent) 

In modern society, people exhibit more sedentary behaviour (SB), which has profound impacts on people’s health. Previous meta-analyses have shown increased SB increasing all around mortality, while increasing physical activity (PA) levels was seen with a corresponding decrease. This study, using data from UK Biobank and the US based National Health and Nutrition Examination Survey (NHANES) examined the connection between SB and cause-specific and all-cause mortality, while also using the isotemporal model (ISM) to discover which types of PA were best suited to replace SB. A total of 490,659 individuals were included for the Biobank cohort while 33,534 individuals were included for the NHANES cohort. SB was defined as time on a computer, driving, or watching TV and grouped into < 5 hours a day, 5-8 hours a day and > 8 hours a day. PA was self-defined, categorized by sports, exercise, light/heavy DIY and walking, while for NHANES it was recreational/work activities, further divided into moderate/vigorous, and walking/cycling for transportation. The Biobank and NHANES data pool saw 36,109 and 3057 deaths recorded respectively. A substantial increase for all-cause mortality was seen in individuals with SB > 8 hours a day (HR 1.412, 95% CI 1.100–1.186 for the UK Biobank; HR 1.695, 95% CI 1.525–1.883 for the NHANES) compared to those with < 5. The greatest 3 specific causes of mortality risk seen were respiratory disease (HR 1.347, 95% CI 1.149–1.579 for the UK Biobank; HR 2.355, 95% CI 1.517–3.468 for the NHANES), cardiovascular disease (CVD) (HR 1.347, 95% CI 1.149–1.579 for the UK Biobank; HR 2.355, 95% CI 1.517–3.468 for the NHANES), and cancer (HR 1.106, 95% CI 1.047–1.167 for the UK Biobank). With regards to ISM, a replacement of 30 minutes of SB with PA saw a decrease of mortality of 5.1% in Biobank (HR 0.949, 95% CI 0.943–0.955) and 5.5% in NHANES (HR 0.945, 95% CI 0.933–0.957). Increasing PA intensity saw even greater reductions in all-cause and specific mortalities. Overall, SB was associated with increased risk of all-cause mortality and mortality due to respiratory disease, CVD, and cancer. 

Click to read the study in BMC Medicine

Image: PD

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