Amount and intensity of physical activity and risk of incident cancer in the UK Biobank

Abstract

Importance: The influence of total daily and light intensity activity on cancer risk remains unclear, as most existing knowledge is drawn from studies relying on self-reported leisure-time activities of moderate-vigorous intensity.

Objective: To investigate associations between total daily activity, including step counts, and activity intensity on incident cancer risk.

Design setting and participants: Prospective analysis of cancer-free UK Biobank participants who wore accelerometers for 7-days (between 2013-2015), followed for cancer incidence through national registries (mean follow-up 5.8 years (SD=1.3)).

Exposures: Time-series machine learning models derived daily total activity (average acceleration), behaviour time, step counts, and peak 30-minute cadence from wrist-based accelerometer data.

Main outcomes and measures: A composite cancer outcome of 13 cancers previously associated with low physical activity (bladder, breast, colon, endometrial, oesophageal adenocarcinoma, gastric cardia, head and neck, kidney, liver, lung, myeloid leukaemia, myeloma, and rectum) based on previous studies of self-reported activity. Cox proportional hazards regression models estimated hazard ratios (HR) and 95% confidence intervals (CI), adjusted for age, sex, ethnicity, smoking, alcohol, education, Townsend Deprivation Index, and reproductive factors. Associations of reducing sedentary time in favour of increased light and moderate-vigorous activity were examined using compositional data analyses.

Results: Among 86 556 participants (mean age 62.0 years (SD=7.9) at accelerometer assessment), 2 669 cancers occurred. Higher total physical activity was associated with a lower overall cancer risk (HR_1SD=0.85, [95%CI 0.81-0.89]). On average, reallocating one hour/day from sedentary behaviour to moderate-vigorous physical activity was associated with a lower risk (HR=0.92, [0.89-0.95]), as was reallocating one hour/day to light-intensity physical activity (HR=0.94, [0.92-0.96]). Compared to individuals taking 5 000 daily steps, those who took 9 000 steps had an 18% lower risk of physical-activity-related cancer (HR=0.82, [0.74-0.90]). We found no significant association with peak 30-minute cadence after adjusting for total steps.

Conclusion and relevance: Higher total daily physical activity and less sedentary time, in favour of both light and moderate-vigorous intensity activity, were associated with a lower risk of certain cancers. For less active adults, increasing step counts by 4 000 daily steps may be a practical public health intervention for lowering the risk of some cancers.

Figure 1.

Association of mean accelerometer-measured physical activity with risk of incident cancers in 86 556 UK Biobank participants. The standard deviation (SD) of total physical activity (PA) was 8.3 milligravity unit in the main analytical sample. Hazard ratios (HR) and 95% confidence intervals (CI) were estimated using a Cox proportional hazards regression model. Cases are incident cancers. PA-related cancer was defined as 13 site specific cancers (oesophageal adenocarcinoma, liver, lung, kidney, gastric cardia, endometrial, myeloid leukaemia, myeloma, colon, head and neck, rectal, bladder, and breast). Models used age as the underlying time variable and were adjusted for sex, ethnicity, smoking status, alcohol consumption, deprivation, and education. For breast cancer and endometrial cancer, models were adjusted for use of oral contraception, use of hormone replacement therapy, menopausal status, and parity. Participants were limited to males for prostate cancer (N=38 078), females for breast cancer (N=48 478), and females without a history of hysterectomy for endometrial cancer (N=41 010).

Figure 2.

Hazard ratios for balance between movement behaviours and incident physical-activity-related cancer risk associated in 86 556 UK Biobank participants. Hazard ratios are relative to the mean behaviour composition (8.1 hours/day sleep, 10.5 hours/day sedentary behaviour (SB), 4.9 hours/day light intensity physical activity behaviours (LIPA), 0.46 hours/day (27.4 minutes/day) moderate-vigorous intensity physical activity behaviours (MVPA)). Physical-activity-related cancer was defined as 13 site specific cancers (oesophageal adenocarcinoma, liver, lung, kidney, gastric cardia, endometrial, myeloid leukaemia, myeloma, colon, head and neck, rectal, bladder, and breast). Models used attained age as the underlying time variable and were adjusted for sex, ethnicity, smoking status, alcohol consumption, deprivation, and education. Models are based on 2 669 events in 86 556 participants. hr = hour.

Figure 3.

Dose-response associations between daily step count and physical-activity-related cancer risk in 86 556 UK Biobank participants. Estimated hazard ratios and 95% confidence intervals were computed using a Cox proportional hazards regression model with restricted cubic spline functions. Observations were trimmed at the 1% and 99% of the distribution and 3 knots were placed at the 5th, 50th, and 95^th percentile for the exposures. The ~10th percentile was set as the referent group (5 000 steps). Physical-activity-related cancer was defined as 13 site specific cancers (oesophageal adenocarcinoma, liver, lung, kidney, gastric cardia, endometrial, myeloid leukaemia, myeloma, colon, head and neck, rectal, bladder, and breast). The male model was limited to 38 078 participants and the female model was limited to 48 478 participants. Models used attained age as the underlying time variable and were adjusted for ethnicity, smoking status, alcohol consumption, deprivation, and education. The overall model (A) was further adjusted for sex and the female model (C) was further adjusted for use of oral contraception, use of hormone replacement therapy, menopausal status, and parity. The shading on the lower axis represents sample clustering of daily step counts.