Reallocation of 24-hour movement behaviour composition and mortality: exploring effect modification by sleep...

Sleep, sedentary behaviour (SB), standing, light-intensity physical activity (LPA) and moderate-to-vigorous physical activity (MVPA) compose the 24-hour day, and reallocating time between these behaviours is associated with premature mortality; however, whether these associations differ by sleep characteristics remains unclear. We examined associations between time reallocations across these device-measured behaviours and all-cause, cardiovascular disease (CVD) and physical activity-related cancer mortality, and potential effect modification by sleep duration and regularity. We conducted a population-based prospective cohort study among UK Biobank participants and applied compositional Cox regression. In 68 995 adults, 2668 deaths occurred over a mean follow-up of 8.0 years. Among participants meeting sleep duration guidelines, reallocating 30-minutes from sleep to standing, LPA or MVPA was favourably associated with all-cause mortality, with HRs of 0.85 (95%CI 0.79, 0.92), 0.87 (0.81, 0.94), and 0.80 (0.74, 0.87), respectively. Among short sleepers, reallocating 30-minutes from sleep to SB, standing or LPA was adversely associated with CVD mortality, with HRs of 1.18 (1.04, 1.34), 1.20 (1.04, 1.38), and 1.18 (1.03, 1.35), respectively. Beneficial associations of reallocating SB to sleep were evident among both regular sleepers and irregular sleepers. These observational findings suggest that associations between 24-hour behavioural reallocations and mortality may vary according to sleep characteristics.