Background
Circadian rhythm disruptors (e.g., night shift work, light at night) have emerged as risk factors for breast cancer, however evidence on their influence on prognosis is limited. A small but growing body of literature suggests mechanistic behaviours underpinning circadian rhythm disruption (i.e., sleep patterns and eating behaviours) may influence breast cancer outcomes, though this evidence is yet to be summarised. Given that breast cancer survivors experience altered eating and sleeping patterns following a cancer diagnosis, understanding the association between post-diagnosis behaviours and outcomes is important to inform interventions targeting these behaviours. Therefore, we systematically summarised literature examining the influence of post-diagnosis circadian rhythm disrupting behaviours on cancer outcomes in women with breast cancer.
Methods
A systematic search of five databases from inception to January 2021 was conducted. Original research published in English, assessing the relationship between post-diagnosis sleeping patterns and eating behaviours, and breast cancer outcomes were considered. Risk of bias was assessed using the Newcastle-Ottawa Assessment Scale for Cohort Studies.
Results
Eight studies published original evidence addressing sleep duration and/or quality (k[number of studies]=7) and, eating time and frequency (k=1). Longer sleep duration (>9h versus [referent range] 6-8h) was consistently associated with increased risk of all outcomes of interest (HR range: 1.37-2.33). There was limited evidence to suggest that higher sleep quality is associated with lower risk of all-cause mortality. Shorter nightly fasting duration (<13h versus ≥13h) was associated with higher risk of breast cancer outcomes (HR range: 1.21-1.36).
Conclusion
Our review suggests that circadian rhythm disrupting behaviours influence cancer outcomes in women with breast cancer. While causality remains unclear, to further understand these associations future research directions have been identified. Additional well-designed studies, examining other exposures (e.g., light exposure, temporal eating patterns), biomarkers, and patient-reported outcomes, in diverse populations (e.g., breast cancer subtype-specific, socio-demographic diversity) are warranted.