Associations of adiposity and device-measured physical activity with cancer incidence: UK Biobank prospective cohort study.

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High adiposity and low physical activity are associated with cancer risk. Whether different amounts and intensities of physical activity can mitigate this association is unclear. We aimed to examine the independent and combined associations of adiposity and device-measured physical activity levels of different intensities with cancer incidence and mortality. This prospective cohort study included data from 70,747 UK Biobank participants (mean age 61.6 ± 7.9 years, 56.4% women) with wrist-worn accelerometer measurements of physical activity and without chronic diseases or mobility limitations. Physical activity exposures included min per week of light (LPA), moderate-to-vigorous (MVPA), and vigorous (VPA) intensity physical activity, along with total weekly volume. Body mass index (BMI) was calculated from anthropometric measurements. Participants were categorized into 9 groups based on joint tertiles of physical activity and BMI categories (normal weight, overweight, and obesity). Secondary analyses included adiposity using bio-impedance and waist circumference measurements. The outcome was incidence and death from cancer retrieved from national registries. Associations between adiposity, physical activity, and cancer hazard were calculated as subdistribution hazard ratios. A secondary analysis focused on cancer types strongly associated with physical activity. We observed 2625 events (2572 non-fatal and 53 fatal) during a median follow-up of 6.1 years. Compared with the referent (normal weight and high physical activity), overweight and obesity were associated with a 6% to 36% higher cancer hazard across physical activity intensities. However, high MVPA and VPA (approximately 500 min and 32 min per week in the top tertiles, respectively) attenuated the hazard associated with overweight and obesity. Being normal weight was not associated with a higher cancer hazard regardless of physical activity level. The results were similar, although more pronounced, when modeling cancer types strongly associated with physical activity as the outcome. High MVPA and VPA levels may attenuate the association of overweight and obesity with cancer hazard, but maintaining a normal weight seems comparatively more important than physical activity to reduce the hazard. Maintaining a healthy body weight and engaging in physical activity is needed to minimize risk of some cancer types.