Amount and intensity of daily total physical activity, step count and risk of incident cancer in the UK Biobank.

ObjectivesTo investigate associations between daily physical activity, activity intensity and step counts with incident cancer risk.MethodsProspective 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.ResultsAmong 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.ConclusionTotal physical activity, LIPA, MVPA and step counts were inversely associated with incident cancer.