Sedentary time associated with poor health independent of physical activity

1. Prolonged sedentary time was associated with increased risk for all-cause mortality, cardiovascular disease incidence and mortality, cancer incidence and mortality, and type-2 diabetes, regardless of physical activity.

2. The effect on negative outcomes associated with sedentary time was decreased among people who participated in higher levels of activity compared to lower levels.

Evidence Rating Level: 2 (Good)

Study Rundown: Preventive health guidelines recommend that adults achieve a minimum of 150 minutes of physical activity per week. However, the extent to which sedentary time is associated with negative health effects is unclear. This meta-analysis sought to evaluate the association between sedentary time and health outcomes, while adjusting for participation in physical activity. Increased sedentary time was associated with increased risk for all-cause mortality, cardiovascular disease mortality, cancer mortality, cardiovascular disease incidence, cancer incidence, and type 2 diabetes incidence. The largest effect was seen with diabetes, where the risk almost doubled at higher sedentary time. With regards to cancer mortality and incidence, the analysis showed significant associations with breast, colon, colorectal, endometrial, and epithelial ovarian cancer. An Australian study included in the meta-analysis also demonstrated a lower risk for preventable hospitalization when patients reported less than 8 hours of sitting time a day. Studies that measured joint effects of sedentary time and physical activity demonstrated that the effects of sedentary time were more pronounced when physical activity levels were lower. This meta-analysis consisted mainly of prospective-cohort studies, as no RCTs met inclusion criteria. The statistical analysis was limited by the practice of self-reporting of physical activity and the variable definition of sedentary time across studies.

Click to read the study today in The Annals of Internal Medicine

Relevant Reading: CDC Guidelines for Physical Activity

In-Depth [meta-analysis]: The analysis included primary research studies that assessed sedentary behavior as a direct predictor associated with at least one health outcome. Forty-one studies were identified from a literature database search. All but three were prospective-cohort studies, while the remainder used cross-sectional and case-control study designs. Study analysis revealed trends of publication bias and high heterogeneity in studies reporting all-cause mortality, but low heterogeneity for cardiovascular mortality, cancer mortality and incidence, and type 2 diabetes. Sedentary behavior was broadly defined as behaviors of low-energy, like sitting and television watching. The meta-analysis produced hazard ratios of 1.24 for all-cause mortality (95%CI 1.09-1.41), 1.91 for type 2 diabetes (95%CI 1.64-2.22), 1.14 for cardiovascular disease incidence (95%CI 1.00-1.30), 1.18 for cardiovascular disease mortality (95%CI 1.11-1.24), 1.13 for cancer incidence (95%CI 1.05-1.21), and 1.16 for cancer mortality (95%CI 1.10-1.22). For joint effects, low physical activity with a high sedentary time produced a hazard ratio of 1.46 (95%CI 1.22-1.75).

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