Sedentary behaviours, cognitive function and possible mechanisms in older adults - A systematic review

Background: Physical activity can improve cognitive function of older adults, but the influence of sedentary behaviour on cognition is less clear. This systematic review investigated associations between sedentary behaviour and cognitive function in older adults without dementia, and possible mechanisms involved. Methods: Major databases were searched for studies in English between 01/01/1999 and 31/10/2019. The systematic review followed COSMOS-E guideline and a pre-registered protocol (CRD42019122229). Risk of bias was assessed using NICE Quality appraisal checklist. Findings were narratively synthesized and presented. Findings: Eighteen studies comprised of Thirteen cross-sectional and five longitudinal analyses (n= 40,228). Evidence suggested varied associations between varied sedentary behaviours and cognitive function in older adults. 50% of study analyses did not control for physical activity. 3/18 studies demonstrated associations between higher sedentary levels and lower levels of brain biomarkers, while 1/18 showed auto-regulatory effect in the left hippocampus. Conducting a meta-analysis was not justifiable due to considerable methodological, participant, outcome and exposure heterogeneity. Conclusion: There is a lack of clarity about the overall and independent association between sedentary behaviour and cognition in older age. Underlying mechanisms are similar to physical activity and probably multi-modal. More studies with robust designs and methodology are needed to confirm effect of sedentary behaviour on cognition.