Reallocation of 24-hour physical behaviour composition and mortality: exploring effect modification by sleep characteristics

Time compositions of physical behaviours are associated with premature mortality, but the moderating role of sleep remains unclear. Using data from the UK Biobank accelerometry subsample, we examined associations of time reallocations between five device-measured physical behaviours (sleep, sedentary behaviour (SB), standing, light-intensity (LPA) and moderate-to-vigorous physical activity (MVPA)) with all-cause, cardiovascular disease (CVD) and physical activity-related cancer mortality, and the potential effect modification by sleep duration and regularity. Compositional Cox regression was used to examine associations of behavioural reallocations with mortality. In 58,149 adults, 2,209 deaths occurred over a mean follow-up of 8.0 years. Among participants who meet sleep duration guidelines, reallocating 30 minutes from sleep to standing, LPA or MVPA was favourably associated with all-cause mortality with HRs of 0.86 (95%CI 0.79, 0.93), 0.87 (0.80, 0.95), and 0.80 (0.73, 0.87), respectively. Reallocating 30 minutes from sleep to SB, standing, or LPA was adversely associated with CVD risk (HRs 1.08 (1.02, 1.15), 1.10 (1.01, 1.20), and 1.11 (1.03, 1.20)) among those not meeting guidelines. Beneficial associations of reallocating SB to sleep were evident only amongst short (<7h/day) or regular (SRI>87.8) sleepers across mortality outcomes. Our findings support incorporating sleep characteristics into future personalised behavioural interventions design and behavioural targets.