Targeting Circadian Rhythms to Improve Fatigue, Sleep, and Depressed Mood in Cancer Rehabilitation - Lisa Wu

Background
Cancer survivors frequently experience persistent fatigue, sleep disturbance, and depressed mood during and after treatment, leading to substantial impairments in quality of life. Circadian rhythm disruption has emerged as an important mechanism that may contribute to these interrelated symptoms. Such disruption can arise from the cancer itself, as well as from cancer treatments, hospitalization, reduced daytime light exposure, and behavioural changes that interfere with normal circadian entrainment.

Objective
This programme of research aims to examine the circadian system as a modifiable target in cancer care and rehabilitation, with a particular focus on light exposure as a non-pharmacological strategy to support circadian regulation and symptom management.

Methods
Across a series of observational and randomized studies conducted in both inpatient and outpatient cancer survivor populations, we have investigated associations between light exposure, circadian disruption, and cancer-related symptoms. Observational studies have leveraged variation in hospital room assignment and associated environmental light exposure to examine differences in symptom trajectories during hospitalization. Complementary randomized studies have evaluated circadian-informed manipulation of environmental and individual light exposure in both inpatient and outpatient settings. Outcomes assessed across studies include fatigue, sleep disturbance, and mood-related symptoms.

Results
Across this body of work, symptom trajectories have been examined in relation to light exposure under varying clinical contexts, comparator conditions, and stages of treatment. Findings suggest that light exposure is relevant to cancer-related symptom experiences, while also demonstrating heterogeneity across settings and study designs, underscoring the complexity of circadian influences during cancer care.

Conclusion
Together, these findings provide cautious support for light exposure as a relevant component of circadian-informed approaches to the prevention and management of cancer-related symptoms. The work highlights the importance of timing, setting, and environmental context when considering light-based strategies. Further research is needed to clarify the mediating role of circadian disruption, including the extent to which changes in circadian rhythm characteristics account for differing symptom trajectories. Ongoing work is extending beyond single-component interventions toward more integrated circadian-informed approaches in cancer rehabilitation.