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Isotemporal substitution of sedentary time by physical activity of different intensities and bout lengths, and its associations with metabolic risk

Background Time spent being sedentary, regardless of time in exercise, has been associated with metabolic risk using regression modelling. By using isotemporal substitution modelling, the effect of replacing sedentary time with an equal amount of time in physical activity (PA) of different intensities can be considered. The present study aims to investigate the effect of replacing sedentary time with time in light, moderate and vigorous PA to the prevalence of the metabolic syndrome (MetS). Also, replacement of sedentary time by PA of different bout lengths was studied. Methods In total, 836 participants (52% women), aged 50–64 years, from the SCAPIS pilot study were included. Daily time spent sedentary and in PA of different intensities was assessed using hip-worn accelerometers. Results In this cross-sectional study, replacing 10 minutes of sedentary time with the same amount of light PA was associated with significant lower MetS prevalence, odds ratio (OR) 0.96 (95% confidence interval 0.93–0.98). Replacement with moderate PA resulted in even lower OR, 0.89 (0.82–0.97), with the lowest OR for vigorous PA, 0.41 (0.26–0.66). Participants with high energy intake and high daily sedentary time benefitted more from the replacement of sedentary time with light PA. Significant associations were seen for all bout lengths of light, moderate and vigorous PA in a stepwise-like fashion from one minute to up to 120 minute bouts. Conclusion Theoretical substitutions of sedentary time with PA of any intensity and of as little as one minute were associated with significantly lower ORs for MetS. This may be an easily communicable message in clinical practice and for public health purposes.