Background: In today’s society, adults are spending increasing amounts of time in sedentary behaviours. This is of concern as sedentary behaviour has been identified as an important and independent risk factor for the development of type 2 diabetes and cardiovascular disease. An increasing amount of evidence from cross-sectional and prospective studies suggests that sedentary behaviour is associated with obesity, independent of physical activity yet the magnitude and consistency of the association remains unclear.
Objective: To conduct a systematic review and meta-analysis to quantify the association between sedentary behaviour and obesity related outcomes in healthy adults, independent of physical activity.
Design: The systematic review was done according to the general guidance of the Cochrane Collaboration guidelines. English language studies published between 1946 to July 2015 were identified via six electronic databases in Ovid MEDLINE, MEDLINE Pending via Ovid, EMBASE via Ovid, EMBASE Classic via Ovid, AMED and PubMed. In addition, citation searches were conducted for relevant studies published after 2011 and for systematic reviews. Criteria for eligibility of studies included: prospective studies of at least 1-year follow-up and randomised control trails of at least 12 weeks that examined the association between sedentary behaviour and obesity related outcomes (body weight, BMI, waist circumference, risk of obesity) in healthy adults, independent of physical activity. Two authors independently extracted and transformed data. Summary estimates were calculated by meta-analysis using a random-effects model (STATA version 12.1).
Results: From the 14,647 studies identified, 16 prospective studies (432,010 participants) met our eligibility criteria for the meta-analysis. The pooled summary effects showed no significant association between sedentary behaviour and all obesity related outcomes with the exception of waist circumference. Each additional hour per day for change in sedentary time corresponded to an increase in waist circumference of 0.27 cm (95% CI, 0.04, 0.50; P = 0.023) over five years (see figure 7). We found no association between sedentary time and risk of obesity, 17% (95% CI, 0.77, 1.80; P = 0.459), and BMI, 0.11 kg/m2 (95% CI, -0.16, 0.38; P = 0.418). Likewise, we did not find a dose-response association between sedentary time (1 h per d) and change in BMI, 0.04 kg/m2
(95% CI, -0.04, 0.13; P = 0.292), change in body weight, 0.05 kg (95% CI, -0.00, 0.10; P = 0.066) or change in waist circumference, -0.04 cm (95% CI, -0.26, 0.18; P = 0.715) over five years. Finally, we found no dose-response association between a change in sedentary time (1 h per d) and change in body weight, 0.38 kg (95% CI, -0.09, 0.86; P = 0.111).
Conclusion: The findings of this review suggest there is limited evidence of a meaningful association between sedentary behaviour and obesity in healthy adults, independent of physical activity.
