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Objective - Accelerometer

635. Reconsidering the Sedentary Behaviour Paradigm

Research Article
Carol Maher, Tim Olds, Emily Mire, Peter T. Katzmarzyk
July 2014

Commentary: Adrian Bauman, Co-Director GlobalPANet, University of Sydney, Australia

This study looked at a cross sectional analysis of NHANES, data from the USA, examining information from 4600 adults. The key question in this cross sectional analytic study was whether sedentary behaviour was independently associated with other biomarkers known to be cardiovascular and metabolic risk factors. The study used objective measurement of sedentary time and physical activity [with accelerometers]. 

The findings of this study were that sedentary behaviour (SB) was associated with 8 of 11 biomarkers including blood sugar level, measures of insulin and resistance, measures of blood pressure and waist circumference.  However, adjusting for moderate and vigorous physical activity minutes reduced these associations such that they were only four biomarkers left that were significantly associated with SB.  Further, adjusting for total physical activity counts on accelerometry only left C reactive protein as significantly associated with sedentary behaviour, as well as triglycerides, but the association for the latter biomarker was in the wrong direction.  These data suggest that the effects of sedentary behaviour or their relationships between sedentary behaviour and other biomarkers maybe moderated by total physical activity.

This is the kind of paper which challenges conventional thinking in an area, and this is important in epidemiology.  Firstly, this study is limited by being a cross sectional study, but much of the evidence on sedentary behaviour has come from other studies that are also cross sectional associations with biomarkers.  Perhaps this study is over adjusting, or perhaps the relationship is partly moderated by physical activity.  If so, then the risk of sedentary behaviour would be particularly notable among people who are insufficiently physically active, and by contrast, those who are regularly physical active may suffer minimal additional risk from prolonged sedentary behaviours!  This statement then becomes “a controversy” in the scientific, epidemiological and public health literature around sedentary behaviour and sitting time, and the findings of this study by Maher and colleagues have therefore created substantial interest and debate.  

This is an important study because it generates debate, because it makes us question us what we think might be happening in understanding sedentary behaviour, and really points to the need to clarify some of the relationships between sedentary behaviour and biomarkers or health outcomes, more carefully considering the interaction with physical activity, and completing this research more fully prior to developing public health guidelines or recommendations in this area.

Source: PLoS ONE 9(1): e86403. Access to this article may depend on your Institutional rights. Click here for the full article.