Interrelationships among sedentary behaviour, short sleep and the metabolic syndrome in adults
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Background: Sedentary behaviour is waking activity in a seated or reclined position that involves little energy expenditure. It is gaining attention as an important cardiometabolic risk factor, independent of physical activity. Studies assessing the relationship between sedentary behaviour and cardiometabolic risk have not accounted for sleep duration as a potential covariate, although there is evidence that sleep duration may be related to both sedentary behaviour and cardiometabolic risk. Objectives: To examine the associations between sleep duration and sedentary behaviour in adults, and determine if sedentary behaviour is related to the metabolic syndrome (MetS) after controlling for sleep duration. Methods: This cross-sectional study used data from the 2003-2006 National Health and Nutrition Examination Survey, a representative sample of Americans. There were 1371 adults over the age of 20 that were studied. Average daily sedentary time and sleep duration were determined via 7-day accelerometry. Screen time (television, computer) was determined via questionnaire. The MetS was determined using standard criteria. Analysis of variance was used to examine relationships among sedentary time and screen time with sleep duration. Multiple logistic regression was used to examine associations between total sedentary time, screen time, and sleep duration with the MetS after controlling for several covariates. Results: Sedentary time and screen time did not vary across sleep duration quartiles (p=0.08 and p=0.87, respectively), and therefore were unrelated to sleep duration. The relative odds of the MetS was significantly higher in participants in the highest quartile of sedentary time than in participants in the lowest quartile (OR=1.60, 95% CI:1.05-2.45). The relative odds of the MetS was higher in participants in the highest screen time tertile than in participants in the lowest tertile (OR =1.67, 95% CI:1.13-2.48). Short sleep duration was not independently related to the MetS, but was borderline related to waist circumference (OR=1.25, 95% CI:0.85-1.84). Conclusion: Highly sedentary individuals and individuals with a high screen time are more likely to have the MetS, independent of sleep duration. Future studies in this area would benefit from using more advanced objective measures of sedentary behaviour and sleep duration and a prospective study design.