Examining Mediators of the Effects of Yoga on Sleep in Breast Cancer Patients Undergoing Chemotherapy

Yoga has been increasingly utilized as a complementary therapy by cancer patients. Literature supports the use of yoga therapy as a prophylactic intervention that can improve sleep and preserve the long-term QOL outcomes for patients. Investigation of the mechanisms by which yoga impacts mental and physical health-related outcomes, including sleep, in breast cancer patients is essential to inform potential interventions to potentially address poorer cancer-related outcomes. Previous research suggests that yoga may impact the way in which a traumatic experience, such as cancer diagnosis and treatment, is processed. The effect of yoga on posttraumatic stress and growth may account for the positive effect of yoga on physical and mental health outcomes in cancer patients, but this relationship has been insufficiently explored. The current study is a secondary analysis of a randomized controlled trial of a Tibetan yoga program compared to active and waitlist control groups. The present study aimed to assess if the effect of group (i.e. yoga, stretching, and usual care) on perceived sleep daily disturbances (measured by Pittsburg Sleep Quality Index (PSQI) daily disturbance component (PSQI-DD), objective sleep (i.e. sleep efficiency (SE) and wakefulness after sleep onset (WASO), measured by wrist actigraphy) and in breast cancer patients undergoing chemotherapy is mediated by changes in posttraumatic stress (PTSS, measured by Impact of Event Scales, IES-intrusion, IES-avoidance, IES-total) and posttraumatic growth (PTG, measured by Posttraumatic Growth Inventory (PTGI)). No significant relative indirect effect using the conditional indirect mediation model (Model 4), a 1000-sample bootstrap procedure to estimate bias-corrected 95% confidence intervals (CIs) was found. Further exploratory analysis on if the effect of group on 3-month health related Quality of Life (QOL, measured by SF-36 mental health and physical health component score (MCS and PCS)) is mediated by 1-week PTSS and PTG also found no significant indirect mediation. The understanding of how a yoga intervention impacts breast cancer patients’ sleep and QOL, through mediators such as PTG and PTSS, will further support the utility of such complimentary therapies.