Differential associations of mentally-active and passive sedentary behaviours and physical activity with putative cognitive decline in healthy individuals and those with bipolar disorder: Findings from the UK Biobank cohort

Objective: Physical activity confers protection against age-related cognitive dysfunction, but less is known about whether cognition is impacted by sedentary behaviour, specifically its mentally-active and passive forms. Both physical inactivity and sedentary behaviour are highly prevalent in bipolar disorder (BD), yet if and how they relate to the disorder's cognitive symptoms remains unclear. In this study, we explored whether individual variation in physical activity and sedentary behaviour was directly associated with cognition and/or moderated the extent of decrements in cognitive performance occurring as a function of age in people with BD versus psychiatrically-healthy controls.Methods: Relevant UK Biobank data were available for 1074 BD patients and 59,653 psychiatrically-healthy controls, aged 40-70. Age, mentally-active (computer use) and passive sedentary behaviour (TV viewing), physical activity, diagnosis, and their interactions were regressed on a global cognitive score.Results: Cognition was inversely associated with physical activity (8 =-0.003, CI:-0.003,-0.003) and mentally-passive sedentary behaviour (8 =-0.03, CI:-0.04,-0.02) and positively associated with mentally -active sedentary behaviour (8 = 0.13, CI: 0.12, 0.15). The latter association was stronger in the BD group. Mentally-active sedentary behaviour moderated the age-cognition association in both BD patients and controls (8 = 0.01, CI: 0.008, 0.01), such that age-related decrements in cognition were more apparent in those who engaged in less mentally-active sedentary behaviours compared to those who engaged in more.Conclusions: Mentally-active sedentary behaviour may not only attenuate age-related cognitive dysfunction, but may be important for cognition irrespective of age, particularly in those with BD. These findings support the notion that intellectual stimulation is a protective factor conferring cognitive benefits, even in the context of a sedentary lifestyle.