Reallocating Time to Physical Activity and Sleep: Associations with Body Mass Index in Cancer Survivors

Background: Body mass index (BMI) above ≥ 25 kg/m² is associated with increased risk for cancer-related morbidity and mortality. Achieving recommended amounts of physical activity (PA), sedentary time (ST), and sleep can help cancer survivors (CS) attain a healthy BMI. This cross-sectional study examined the potential role of reallocating time between moderate and light PA, ST, and sleep on BMI in CS.

Method: A sample of CS (N = 73, M_age = 53.7 ± 12.9) wore an activPAL and Actiwatch accelerometer for 7 days, 24 h per day to measure PA intensity and sleep, respectively. Self-reported height and weight or scale/stadiometer were used to calculate BMI. Isotemporal substitution models were used to reallocate time, averaged over the 7-day period, from one activity of interest to another and examine the associations with BMI. Statistical significance was set at p < .05.

Results: The following reallocations of 30 min were significantly associated with BMI: sleep to ST (+ 0.80 kg/m², p = 0.02) and ST to light PA (- 0.53 kg/m², p = 0.008). No significant associations with BMI were observed for reallocating time to or away from moderate-vigorous PA.

Conclusion: The results of this study suggest that sleep and light PA may have important implications for achieving a healthy BMI in CS. Therefore, future research should include interventions which target light PA and sleep to determine if they can improve BMI in CS.