Participants in this study reported poor sleep quality and high levels of sleep disruption on the PSQI. Most of the women (70.8%) had PSQI global scores above the established cutoff of 5.0. Additionally, more than half of the women scored above the suggested adjusted cutoff of 8.0 (M
= 8.49) for cancer patients [9
]. This is higher than had previously been found among women with BCa prior to adjuvant treatment, where the mean score was 7.0 [2
]. It is, however, nearly the same as the average score of 8.45 found among women who were, on average, one-year post-diagnosis [19
Higher PSQI Global score was significantly associated with poorer functional well-being, greater fatigue intensity, greater disruptions in social interactions, and lower positive states of mind. Not surprisingly, the component scores were highly correlated with the global score, but the correlation between the SE and SQ component scores was .61. Examination of the component scores showed that lower SQ was associated with all of the outcomes except the SIP–R, while the poorer SE was associated with poorer functional quality of life and the SIP–S. Based on these findings, it seems that the SQ subscales (i.e., sleep disturbances, sleep latency, daytime dysfunction, and sleep quality) have a greater impact on psychosocial outcomes than the actual amount of hours spent in bed and sleeping, and may be a more salient sleep intervention target. These results are similar to those previously reported [2
]; however, with the addition of relevant controls, we now have a clearer picture of the unique contribution of sleep features to psychosocial adaptation. While these contributions are small in some cases, they reached statistical significance in the context of an intervention that was not specifically focused on sleep.
Several limitations should be noted. First, these analyses were exploratory and specific sleep analyses were not planned prior to data collection. Second, sleep variables were limited to the PSQI, a retrospective, self-report measure that covers a one-month time period. Biases related to self-report measures and recall biases may have influenced the data. Also, the measures used in these analyses had varying time frames, from 24-hours (e.g., pain item) to the entire experience of having breast cancer (e.g., FWB), and it is possible that this attenuated relationships between sleep and the psychosocial outcomes. Third, no data was available for participant–s sleep habits prior to enrollment. Fourth, this study was conducted with women diagnosed with stage I–III BCa before adjuvant treatment and therefore, may not generalize to women diagnosed with metastatic BCa or at other phases of treatment. Finally, it is not clear whether there was sufficient variance in the measures as is needed to detect possible correlations between measures and associations between variables may be underestimated.
Choosing the most expeditious intervention to improve either sleep (cognitive behavioral sleep therapy) [20
] or psychosocial adaptation (cognitive behavioral stress management) [7
] may actually bring about benefits in both sleep and psychosocial adaptation. There is emerging evidence to suggest that sleep and stress may share common neuroendocrine mechanisms in the context of cancer treatment [21
]. These data suggest that combining sleep-specific interventions with stress management may be a highly efficient approach in women under treatment for BCa.