Novel insights into physical activity in patients with diabetes and atrial fibrillation: a prospective study from the UK Biobank

Background Patients with coexisting diabetes mellitus (DM) and atrial fibrillation (AF) face exceptionally high all-cause and cardiovascular mortality, yet specific physical activity recommendations are lacking. While guidelines generally recommend moderate-to-vigorous physical activity (MVPA), its safety and efficacy in this fragile population remain unclear compared to lighter intensities. We aimed to quantify the associations of accelerometer-measured sedentary behavior (SED), light physical activity (LPA), and MVPA with mortality, specifically testing the effects of time reallocation between behaviors. Methods Adults with DM and AF from the UK Biobank accelerometer cohort underwent 7-day wrist monitoring. Time in SED, LPA, and MVPA was derived using validated algorithms. Multivariable Cox models and restricted cubic splines characterized dose response relations. Time-reallocation analyses estimated risk changes when substituting fixed durations among behaviors. Results Over a median 8.16 years, 243 deaths occurred (103 CV deaths). Per-SD higher LPA was associated with lower all-cause and CV mortality (HR 0.78, 95% CI 0.68-0.90; and 0.71, 0.57-0.89). Conversely, per-SD higher SED related to greater all-cause and CV mortality (HR 1.21, 1.06-1.38; and 1.49, 1.21-1.84). Interpreted on an absolute time scale, each additional SED hour/day conferred a 10% higher all-cause mortality risk and a 22% higher CV mortality risk. These patterns were consistent across univariate and fully adjusted models. In time-reallocation models, replacing 1 hour/day of SED with LPA yielded robust and significant reductions in both all-cause and CV mortality. Crucially, substituting SED with MVPA showed attenuated benefits, and reallocating MVPA to LPA was associated with a trend toward increased mortality risk, suggesting a potential intensity threshold. Conclusions For patients with the dual burden of DM and AF, LPA offers a safer and more effective survival benefit compared to MVPA. Clinical prescriptions for this high-risk cohort should shift focus from aggressive intensity targets to a 'Sit Less, Move Lightly' paradigm.