Background: The magnitude, consistency, and manner of association between sedentary time and outcomes independent of physical activity remain unclear.

Purpose: To quantify the association between sedentary time and hospitalizations, all-cause mortality, cardiovascular disease, diabetes, and cancer in adults independent of physical activity.

Data sources: English-language studies in MEDLINE, PubMed, EMBASE, CINAHL, Cochrane Library, Web of Knowledge, and Google Scholar databases were searched through August 2014 with hand-searching of in-text citations and no publication date limitations.

Study selection: Studies assessing sedentary behavior in adults, adjusted for physical activity and correlated to at least 1 outcome.

Data extraction: Two independent reviewers performed data abstraction and quality assessment, and a third reviewer resolved inconsistencies.

Data synthesis: Forty-seven articles met our eligibility criteria. Meta-analyses were performed on outcomes for cardiovascular disease and diabetes (14 studies), cancer (14 studies), and all-cause mortality (13 studies). Prospective cohort designs were used in all but 3 studies; sedentary times were quantified using self-report in all but 1 study. Significant hazard ratio (HR) associations were found with all-cause mortality (HR, 1.240 [95% CI, 1.090 to 1.410]), cardiovascular disease mortality (HR, 1.179 [CI, 1.106 to 1.257]), cardiovascular disease incidence (HR, 1.143 [CI, 1.002 to 1.729]), cancer mortality (HR, 1.173 [CI, 1.108 to 1.242]), cancer incidence (HR, 1.130 [CI, 1.053 to 1.213]), and type 2 diabetes incidence (HR, 1.910 [CI, 1.642 to 2.222]). Hazard ratios associated with sedentary time and outcomes were generally more pronounced at lower levels of physical activity than at higher levels.

Limitation: There was marked heterogeneity in research designs and the assessment of sedentary time and physical activity.

Conclusion: Prolonged sedentary time was independently associated with deleterious health outcomes regardless of physical activity.

Primary funding source: None.