Associations between the composition of daily time spent in physical activity, sedentary behaviour and sleep and risk of depression: Compositional data analyses of the 1970 British cohort Study

Background: The benefits of moderate to vigorous physical activity(MVPA) in lowering depression risk are well established, but there is mixed evidence on sleep, sedentary behaviour(SB), and light-intensity physical activity(LIPA). These behaviours are often considered in isolation, neglecting their behavioural and biological interdependences. We investigated how time spent in one behaviour relative to others was associated with depression risk. Methods: We included 4738 individuals from the 1970 British Cohort study (age 46 wave). Depression status was ascertained using self-reported doctor visits and prescribed anti-depressant use. MVPA, LIPA, SB and sleep were ascertained using thigh-worn accelerometers worn consecutively for 7 days. Compositional logistic regression was used to examine associations between different compositions of time spent in movement behaviours and depression. Results: More time spent in MVPA, relative to SB, sleep or LIPA, was associated with a lower risk of depression. When modelling reallocation of time (e.g. replacing time in one behaviour with another), replacing sleep, SB or LIPA with MVPA time was strongly associated with lower depression risk. Reallocating time between SB, sleep or LIPA had minimal to no effect. Limitations: Data was cross-sectional, therefore causality cannot be inferred. Accelerometers do not capture SB context (e.g. TV watching, reading) nor separate biological sleep from time spent in bed. Conclusions: Displacing any behaviour with MVPA was associated with a lower risk of depression. This study provides promising support that increasing MVPA, even in small doses, can have a positive impact on prevention, mitigation and treatment of depression.