Association Between Sedentary Time and CVD Risk
Higher average daily sedentary time is associated with a greater risk for cardiovascular disease (CVD). Is there a specific quantitative dose-response association between sedentary time and CVD risk?
MEDLINE and EMBASE databases were searched for all studies published before July 6, 2015, that evaluated the association between sedentary time and incident CVD. The categorical dose-response association was evaluated by comparing the pooled hazard ratio (HR) for incident CVD associated with different levels of sedentary time (vs. lowest sedentary time) across studies. The continuous dose-response association was assessed using random-effects generalized least squares spline models.
Nine prospective cohort studies with 720,425 unique participants (57.1% women; 42.9% men; mean age, 54.5 years) and 25,769 unique CV events had a median follow-up of 11 years. Compared with the lowest sedentary time category (median, 2.5 hours/day), participants in the highest sedentary time category (median, 12.5 hours/day) had an increased risk for CVD (HR, 1.14). However, there was no apparent risk associated with intermediate levels of sedentary time (HR for 7.5 hours/day, 1.02) was found. In continuous analyses, a nonlinear association between sedentary time and incident CVD was found (p for nonlinearity < 0.001), with an increased risk observed for >10 hours of sedentary time per day (pooled HR, 1.08; 95% confidence interval, 1.00-1.14). Five studies reported interaction testing between physical activity levels and sedentary time for CVD risk. The findings were similar when adjusted for physical activity and other CVD risk factors.
The association between sedentary time and the risk for CVD is nonlinear with an increased risk only at very high levels. These findings could have implications for guideline recommendations regarding the risks related to sedentary behavior.
Sedentary time is defined as time spent in activities involving low levels of energy expenditure (1.0-1.5 MET tasks, such as sitting, watching television, driving). There is an association between sedentary time and cardiometabolic biomarkers including triglycerides, glucose intolerance, insulin sensitivity, and C-reactive protein levels at the highest levels of sedentary time. Both short (<5 hours) and long duration of sleep (>9 hours) are associated with classic CV risk factors. Those who exercise in the morning and have a sedentary job may have more than 20 hours of continuous sedentary time. The findings suggest that for those in a sedentary job, there may be a greater metabolic benefit of relatively short duration of moderate exercise several times a day.
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