Nonlinear Associations of Accelerometer-Based Sedentary Time With Cognitive Functions in the UK Biobank

ObjectivesDevice-based sedentary time shows a nonlinear association with incident dementia among older adults. However, associations between sedentary time and cognitive performance have been inconsistent. We examined potential nonlinear associations between sedentary time and performance on cognitive tests among older adults.MethodsWe used data from the UK Biobank and included 32,875 adults aged 60–79. Sedentary time was estimated from a machine learning–based analysis of 1 week of wrist-worn accelerometer data. The primary outcomes were performance on 6 cognitive tests completed online (fluid intelligence test, short-term numeric memory test, symbol substitution test, visual-spatial memory test, alphanumeric, and numeric trail making tests), as well as a composite cognitive score.ResultsExcept for the visual-spatial memory test, nonlinear approaches provided a better fit than linear methods to model the associations of sedentary time with other cognitive outcomes. For these outcomes, segmented regression models showed that, although effect sizes were small, higher sedentary time was associated with better cognitive performance up to a threshold of sedentary time that varied from 9.7 to 12.3 hr per day. Above this threshold, the association between sedentary time and cognitive performance was attenuated toward the null or became negative (for the symbol substitution test only).DiscussionAs accounted by our nonlinear approach, the association between sedentary time and cognitive performance may shift from positive to null or negative above a 10–12-hr threshold among older adults. A combination of device-based and self-report assessments of sedentary behavior is needed to better understand these nonlinear associations.