Mediation and Dose-Response Relationship Among Physical Activity, Daylight Exposure, and Rest-Activity Circadian Rhythm in Patients With Esophageal and Gastric Cancer.

[BACKGROUND] Physical activity and daylight exposure predict rest-activity circadian rhythm (RACR) in patients with cancer. However, whether daylight exposure mediates the relationship between physical activity and RACR and the optimal amounts of physical activity and daylight that benefit RACR remain unclear.

[OBJECTIVES] This study investigated the mediating role of daylight exposure and determined the dose-response relationship among daylight exposure, physical activity, and RACR in patients with cancer.

[METHODS] This cross-sectional exploratory study recruited 319 patients with esophageal and gastric cancer from 2 surgery outpatient departments in Taiwan. Daylight exposure (>500 lux), physical activity (up activity mean), and RACR (midline estimating statistic of rhythm) were measured through actigraphy. Regression was performed, and the receiver operating characteristic curve was plotted.

[RESULTS] Daylight exposure (>500 lux) partially mediated the relationship between physical activity (up activity mean) and RACR (midline estimating statistic of rhythm). The optimal cutoffs for discriminating between satisfactory and poor RACR were 187.43 counts/min for physical activity (sensitivity, 90.3%; specificity, 84.4%) and 35.71 min/d for daylight exposure (sensitivity, 55.9%; specificity, 78.2%).

[CONCLUSIONS] Participants who engaged in physical activity were more likely to receive daylight exposure and experience improved RACR. The optimal level of daylight exposure and frequency of physical activity that can improve RACR in patients with esophageal and gastric cancer are 36 min/d and 187 counts/min, respectively.

[IMPLICATIONS FOR PRACTICE] Healthcare professionals should encourage patients to engage in exercise or physical activity during the daytime to improve their circadian rhythm.