Abstract
OBJECTIVES: To investigate associations between daily physical activity, activity intensity and step counts with incident cancer risk. METHODS: Prospective analysis of UK Biobank participants who wore wrist-based accelerometers for 7 days, followed for cancer incidence (mean follow-up 5.8 years, SD 1.3). Time-series machine-learning models derived total physical activity, sedentary behaviour (SB), light-intensity physical activity (LIPA), moderate-vigorous-intensity physical activity (MVPA) and step counts. The outcome was a composite of 13 cancers previously associated with low physical activity in questionnaire-based studies. Cox proportional hazard models estimated HRs and 95% CIs, adjusted for demographic, health and lifestyle factors. We also explored associations of LIPA, MVPA and SB with cancer risk. RESULTS: Among 85 394 participants (median age 63 (IQR 56-68)), 2633 were diagnosed with cancer during follow-up. Compared with individuals in the lowest quintile of total physical activity (<21.6 milligravity units), those in the highest (34.3+) had a 26% lower cancer risk (HR=0.74 (95% CI 0.65 to 0.84)). After mutual adjustment, LIPA (HR=0.94 (95% CI 0.90 to 0.98)) and MVPA (HR=0.87 (95% CI 0.79 to 0.94)) were associated with lower risk, but SB was not. Similar associations were observed for substituting 1 hour/day of SB with LIPA or MVPA. Daily step counts were inversely associated with cancer, with the dose-response beginning to plateau at around 9 000 steps/day (HR=0.89 (95% CI 0.83 to 0.96) 7000 vs 5000 steps; HR=0.84 (95% CI 0.76 to 0.93) 9000 vs 5000 steps). There was no significant association between stepping intensity (peak 30-minute cadence) and cancer after adjusting for step count. CONCLUSION: Total physical activity, LIPA, MVPA and step counts were inversely associated with incident cancer.