Sedentary behavior and physical activity are longitudinally associated with diurnal cortisol rhythms in individuals up to 1 year after colorectal cancer treatment: A prospective cohort study

Background : Less robust diurnal cortisol rhythms are hypothesized to be associated with fatigue, depressive symptoms, psychological distress, sleep disturbances and poorer quality of life. Sedentary behavior and physical activity may influence cortisol rhythmicity, providing mechanistic leads for intervention strategies. We examined longitudinal associations of accelerometer-assessed sedentary behavior and physical activity with diurnal cortisol patterns among patients with colorectal cancer (CRC) up to 12 months post-treatment. Methods: Among 74 CRC survivors, total and prolonged sedentary time (in bouts ≥30 min), total physical activity (TPA), and relative amplitude of physical activity reflecting day-night contrast in activity were determined with 7-day thigh-worn accelerometry at 6 weeks, 6 months, and 12 months after cancer treatment. Salivary cortisol was sampled five times daily over two consecutive days at each follow-up timepoint. As a comprehensive assessment of diurnal cortisol rhythms, the relative amplitude of cortisol concentration (RA_cort), diurnal slope, area under the curve (AUC) and cortisol awakening response (CAR) were derived as comprehensive measures of diurnal cortisol rhythms. We used confounder-adjusted linear mixed models to estimate overall longitudinal associations, with coefficients (b) reflecting differences in SD outcome units. Results: More total sedentary time (per 2 hours/day) was associated with a weaker decline in cortisol over time and thus a flatter slope (β=0.19; 95%CI=0.06,0.33). More prolonged sedentary time (per 2 hours/day) was associated with a lower RA_cort (β=-0.12; 95%CI=-0.23,-0.01) and flatter cortisol slope (β=0.16; 95%CI=0.04,0.27). More TPA (per 1 hour/day: β=0.23; 95%CI=0.03,0.43) and a higher relative amplitude of physical activity (per SD: β= 3.51; 95%CI=0.10,6.92) were associated with a higher RA_cort. More total sedentary time (per 2 hours/day) was associated with a higher CAR (β=0.14; 95%CI=0.01,0.27). Conclusion: Higher physical activity levels, a larger RA of physical activity, and less sedentary time were associated with more robust diurnal cortisol rhythms, suggesting these behaviors may be targets for interventions aimed at improving cortisol rhythmicity after CRC. Registration: EnCoRe study (https://www.onderzoekmetmensen.nl/).