Continuous Dose-Response Association Between Sedentary Time and Risk for Cardiovascular Disease: A Meta-analysis.

Importance: Prior studies suggest that higher sedentary time is associated with a greater risk for cardiovascular disease (CVD). However, the quantitative, dose-response association between sedentary time and CVD risk is not known.
Objective: To determine the categorical and quantitative dose-response association between sedentary time and CVD risk.
Data Sources: Two independent investigators searched the MEDLINE and EMBASE databases for all studies published before July 6, 2015, that evaluated the association between sedentary time and incident CVD.
Study Selection: Prospective cohort studies with participants 18 years or older that reported the association between sedentary time and incident CVD were included.
Data Extraction and Synthesis: Two independent investigators performed the data extraction and collection using a standardized form. The study quality was assessed using the Newcastle-Ottawa Scale. 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. Data were collected from April 5 to July 6, 2015.
Main Outcomes and Measures: Incident CVD (coronary heart disease, including nonfatal myocardial infarction, stroke, and cardiovascular mortality).
Results: Nine prospective cohort studies with 720 425 unique participants (57.1% women; 42.9% men; mean age, 54.5 years) and 25 769 unique cardiovascular events and a median follow-up of 11 years were included. In categorical analyses, compared with the lowest sedentary time category (median, 2.5 h/d), participants in the highest sedentary time category (median, 12.5 h/d) had an increased risk for CVD (HR, 1.14; 95% CI, 1.09-1.19). However, no apparent risk associated with intermediate levels of sedentary time (HR for 7.5 h/d, 1.02; 95% CI, 0.96-1.08) was found. In continuous analyses, a nonlinear association between sedentary time and incident CVD was found (P for nonlinearity < .001), with an increased risk observed for more than 10 hours of sedentary time per day (pooled HR, 1.08; 95% CI, 1.00-1.14).
Conclusions and Relevance: 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.